\input texinfo @c -*-texinfo-*- @comment ======================================================== @comment %**start of header @setfilename autoconf.info @include version.texi @settitle Autoconf @setchapternewpage odd @ifnothtml @setcontentsaftertitlepage @end ifnothtml @finalout @c @ovar(ARG, DEFAULT) @c ------------------- @c The ARG is an optional argument. To be used for macro arguments in @c their documentation (@defmac). @macro ovar{varname} @r{[}@var{\varname\}@r{]} @end macro @c @dvar(ARG, DEFAULT) @c ------------------- @c The ARG is an optional argument, defaulting to DEFAULT. To be used @c for macro arguments in their documentation (@defmac). @macro dvar{varname, default} @r{[}@var{\varname\} = @samp{\default\}@r{]} @end macro @c Handling the indexes with Texinfo yields several different problems. @c @c Because we want to drop out the AC_ part of the macro names in the @c printed manual, but not in the other outputs, we need a layer above @c the usual @acindex{} etc. That's why we first define indexes such as @c acx meant to become the macro @acindex. First of all, using ``ac_'' @c does not work with makeinfo, and using ``ac1'' doesn't work with TeX. @c So use something more regular ``acx''. Then you finish with a printed @c index saying ``index is not existent''. Of course: you ought to use @c two letters :( So you use capitals. @c @c Second, when defining a macro in the TeX world, following spaces are @c eaten. But then, since we embed @acxindex commands that use the end @c of line as an end marker, the whole things wrecks itself. So make @c sure you do *force* an additional end of line, add a ``@c''. @c @c Finally, you might want to get rid of TeX expansion, using --expand @c with texi2dvi. But then you wake up an old problem: we use macros @c in @defmac etc. where TeX does perform the expansion, but not makeinfo. @c Define an environment variable index. @defcodeindex ev @c Define an output variable index. @defcodeindex ov @c Define a CPP variable index. @defcodeindex cv @c Define an Autoconf macro index that @defmac doesn't write to. @defcodeindex AC @c Define an Autotest macro index that @defmac doesn't write to. @defcodeindex AT @c Define an M4sugar macro index that @defmac doesn't write to. @defcodeindex MS @c Define an index for *foreign* programs: `mv' etc. Used for the @c portability sections and so on. @defindex pr @c shortindexflag @c -------------- @c Shall we factor AC_ out of the Autoconf macro index etc.? @iftex @set shortindexflag @end iftex @c @acindex{MACRO} @c --------------- @c Registering an AC_\MACRO\. @ifset shortindexflag @macro acindex{macro} @ACindex \macro\ @c @end macro @end ifset @ifclear shortindexflag @macro acindex{macro} @ACindex AC_\macro\ @end macro @end ifclear @c @ahindex{MACRO} @c --------------- @c Registering an AH_\MACRO\. @macro ahindex{macro} @ACindex AH_\macro\ @c @end macro @c @asindex{MACRO} @c --------------- @c Registering an AS_\MACRO\. @ifset shortindexflag @macro asindex{macro} @MSindex \macro\ @c @end macro @end ifset @ifclear shortindexflag @macro asindex{macro} @MSindex AS_\macro\ @end macro @end ifclear @c @atindex{MACRO} @c --------------- @c Registering an AT_\MACRO\. @ifset shortindexflag @macro atindex{macro} @ATindex \macro\ @c @end macro @end ifset @ifclear shortindexflag @macro atindex{macro} @ATindex AT_\macro\ @end macro @end ifclear @c @auindex{MACRO} @c --------------- @c Registering an AU_\MACRO\. @macro auindex{macro} @ACindex AU_\macro\ @c @end macro @c @hdrindex{MACRO} @c ---------------- @c Indexing a header. @macro hdrindex{macro} @prindex @file{\macro\} @c @end macro @c @msindex{MACRO} @c --------------- @c Registering an m4_\MACRO\. @ifset shortindexflag @macro msindex{macro} @MSindex \macro\ @c @end macro @end ifset @ifclear shortindexflag @macro msindex{macro} @MSindex m4_\macro\ @end macro @end ifclear @c Define an index for functions: `alloca' etc. Used for the @c portability sections and so on. We can't use `fn' (aka `fnindex), @c since `@defmac' goes into it => we'd get all the macros too. @c FIXME: Aaarg! It seems there are too many indices for TeX :( @c @c ! No room for a new @write . @c l.112 @defcodeindex fu @c @c so don't define yet another one :( Just put some tags before each @c @prindex which is actually a @funindex. @c @c @defcodeindex fu @c @c @c @c Put the programs and functions into their own index. @c @syncodeindex fu pr @comment %**end of header @comment ======================================================== @copying This manual is for @acronym{GNU} Autoconf (version @value{VERSION}, @value{UPDATED}), a package for creating scripts to configure source code packages using templates and an M4 macro package. Copyright @copyright{} 1992, 1993, 1994, 1995, 1996, 1998, 1999, 2000, 2001, 2002, 2003, 2004, 2005, 2006 Free Software Foundation, Inc. @quotation Permission is granted to copy, distribute and/or modify this document under the terms of the @acronym{GNU} Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover texts being ``A @acronym{GNU} Manual,'' and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled ``@acronym{GNU} Free Documentation License.'' (a) The FSF's Back-Cover Text is: ``You have freedom to copy and modify this @acronym{GNU} Manual, like @acronym{GNU} software. Copies published by the Free Software Foundation raise funds for @acronym{GNU} development.'' @end quotation @end copying @dircategory Software development @direntry * Autoconf: (autoconf). Create source code configuration scripts. @end direntry @dircategory Individual utilities @direntry * autoscan: (autoconf)autoscan Invocation. Semi-automatic @file{configure.ac} writing * ifnames: (autoconf)ifnames Invocation. Listing conditionals in source. * autoconf: (autoconf)autoconf Invocation. How to create configuration scripts * autoreconf: (autoconf)autoreconf Invocation. Remaking multiple @command{configure} scripts * autoheader: (autoconf)autoheader Invocation. How to create configuration templates * autom4te: (autoconf)autom4te Invocation. The Autoconf executables backbone * configure: (autoconf)configure Invocation. Configuring a package. * autoupdate: (autoconf)autoupdate Invocation. Automatic update of @file{configure.ac} * config.status: (autoconf)config.status Invocation. Recreating configurations. * testsuite: (autoconf)testsuite Invocation. Running an Autotest test suite. @end direntry @titlepage @title Autoconf @subtitle Creating Automatic Configuration Scripts @subtitle for version @value{VERSION}, @value{UPDATED} @author David MacKenzie @author Ben Elliston @author Akim Demaille @page @vskip 0pt plus 1filll @insertcopying @end titlepage @contents @ifnottex @node Top @top Autoconf @insertcopying @end ifnottex @c The master menu, created with texinfo-master-menu, goes here. @menu * Introduction:: Autoconf's purpose, strengths, and weaknesses * The GNU Build System:: A set of tools for portable software packages * Making configure Scripts:: How to organize and produce Autoconf scripts * Setup:: Initialization and output * Existing Tests:: Macros that check for particular features * Writing Tests:: How to write new feature checks * Results:: What to do with results from feature checks * Programming in M4:: Layers on top of which Autoconf is written * Writing Autoconf Macros:: Adding new macros to Autoconf * Portable Shell:: Shell script portability pitfalls * Portable Make:: Makefile portability pitfalls * Portable C and C++:: C and C++ portability pitfalls * Manual Configuration:: Selecting features that can't be guessed * Site Configuration:: Local defaults for @command{configure} * Running configure Scripts:: How to use the Autoconf output * config.status Invocation:: Recreating a configuration * Obsolete Constructs:: Kept for backward compatibility * Using Autotest:: Creating portable test suites * FAQ:: Frequent Autoconf Questions, with answers * History:: History of Autoconf * Copying This Manual:: How to make copies of this manual * Indices:: Indices of symbols, concepts, etc. @detailmenu --- The Detailed Node Listing --- The @acronym{GNU} Build System * Automake:: Escaping makefile hell * Gnulib:: The @acronym{GNU} portability library * Libtool:: Building libraries portably * Pointers:: More info on the @acronym{GNU} build system Making @command{configure} Scripts * Writing configure.ac:: What to put in an Autoconf input file * autoscan Invocation:: Semi-automatic @file{configure.ac} writing * ifnames Invocation:: Listing the conditionals in source code * autoconf Invocation:: How to create configuration scripts * autoreconf Invocation:: Remaking multiple @command{configure} scripts Writing @file{configure.ac} * Shell Script Compiler:: Autoconf as solution of a problem * Autoconf Language:: Programming in Autoconf * configure.ac Layout:: Standard organization of @file{configure.ac} Initialization and Output Files * Initializing configure:: Option processing etc. * Notices:: Copyright, version numbers in @command{configure} * Input:: Where Autoconf should find files * Output:: Outputting results from the configuration * Configuration Actions:: Preparing the output based on results * Configuration Files:: Creating output files * Makefile Substitutions:: Using output variables in makefiles * Configuration Headers:: Creating a configuration header file * Configuration Commands:: Running arbitrary instantiation commands * Configuration Links:: Links depending on the configuration * Subdirectories:: Configuring independent packages together * Default Prefix:: Changing the default installation prefix Substitutions in Makefiles * Preset Output Variables:: Output variables that are always set * Installation Directory Variables:: Other preset output variables * Changed Directory Variables:: Warnings about @file{datarootdir} * Build Directories:: Supporting multiple concurrent compiles * Automatic Remaking:: Makefile rules for configuring Configuration Header Files * Header Templates:: Input for the configuration headers * autoheader Invocation:: How to create configuration templates * Autoheader Macros:: How to specify CPP templates Existing Tests * Common Behavior:: Macros' standard schemes * Alternative Programs:: Selecting between alternative programs * Files:: Checking for the existence of files * Libraries:: Library archives that might be missing * Library Functions:: C library functions that might be missing * Header Files:: Header files that might be missing * Declarations:: Declarations that may be missing * Structures:: Structures or members that might be missing * Types:: Types that might be missing * Compilers and Preprocessors:: Checking for compiling programs * System Services:: Operating system services * Posix Variants:: Special kludges for specific Posix variants * Erlang Libraries:: Checking for the existence of Erlang libraries Common Behavior * Standard Symbols:: Symbols defined by the macros * Default Includes:: Includes used by the generic macros Alternative Programs * Particular Programs:: Special handling to find certain programs * Generic Programs:: How to find other programs Library Functions * Function Portability:: Pitfalls with usual functions * Particular Functions:: Special handling to find certain functions * Generic Functions:: How to find other functions Header Files * Header Portability:: Collected knowledge on common headers * Particular Headers:: Special handling to find certain headers * Generic Headers:: How to find other headers Declarations * Particular Declarations:: Macros to check for certain declarations * Generic Declarations:: How to find other declarations Structures * Particular Structures:: Macros to check for certain structure members * Generic Structures:: How to find other structure members Types * Particular Types:: Special handling to find certain types * Generic Types:: How to find other types Compilers and Preprocessors * Specific Compiler Characteristics:: Some portability issues * Generic Compiler Characteristics:: Language independent tests and features * C Compiler:: Checking its characteristics * C++ Compiler:: Likewise * Objective C Compiler:: Likewise * Erlang Compiler and Interpreter:: Likewise * Fortran Compiler:: Likewise Writing Tests * Language Choice:: Selecting which language to use for testing * Writing Test Programs:: Forging source files for compilers * Running the Preprocessor:: Detecting preprocessor symbols * Running the Compiler:: Detecting language or header features * Running the Linker:: Detecting library features * Runtime:: Testing for runtime features * Systemology:: A zoology of operating systems * Multiple Cases:: Tests for several possible values Writing Test Programs * Guidelines:: General rules for writing test programs * Test Functions:: Avoiding pitfalls in test programs * Generating Sources:: Source program boilerplate Results of Tests * Defining Symbols:: Defining C preprocessor symbols * Setting Output Variables:: Replacing variables in output files * Special Chars in Variables:: Characters to beware of in variables * Caching Results:: Speeding up subsequent @command{configure} runs * Printing Messages:: Notifying @command{configure} users Caching Results * Cache Variable Names:: Shell variables used in caches * Cache Files:: Files @command{configure} uses for caching * Cache Checkpointing:: Loading and saving the cache file Programming in M4 * M4 Quotation:: Protecting macros from unwanted expansion * Using autom4te:: The Autoconf executables backbone * Programming in M4sugar:: Convenient pure M4 macros * Programming in M4sh:: Common shell Constructs * File Descriptor Macros:: File descriptor macros for input and output M4 Quotation * Active Characters:: Characters that change the behavior of M4 * One Macro Call:: Quotation and one macro call * Quotation and Nested Macros:: Macros calling macros * Changequote is Evil:: Worse than INTERCAL: M4 + changequote * Quadrigraphs:: Another way to escape special characters * Quotation Rule Of Thumb:: One parenthesis, one quote Using @command{autom4te} * autom4te Invocation:: A @acronym{GNU} M4 wrapper * Customizing autom4te:: Customizing the Autoconf package Programming in M4sugar * Redefined M4 Macros:: M4 builtins changed in M4sugar * Looping constructs:: Iteration in M4 * Evaluation Macros:: More quotation and evaluation control * Text processing Macros:: String manipulation in M4 * Forbidden Patterns:: Catching unexpanded macros Writing Autoconf Macros * Macro Definitions:: Basic format of an Autoconf macro * Macro Names:: What to call your new macros * Reporting Messages:: Notifying @command{autoconf} users * Dependencies Between Macros:: What to do when macros depend on other macros * Obsoleting Macros:: Warning about old ways of doing things * Coding Style:: Writing Autoconf macros @`a la Autoconf Dependencies Between Macros * Prerequisite Macros:: Ensuring required information * Suggested Ordering:: Warning about possible ordering problems * One-Shot Macros:: Ensuring a macro is called only once Portable Shell Programming * Shellology:: A zoology of shells * Here-Documents:: Quirks and tricks * File Descriptors:: FDs and redirections * File System Conventions:: File names * Shell Substitutions:: Variable and command expansions * Assignments:: Varying side effects of assignments * Parentheses:: Parentheses in shell scripts * Slashes:: Slashes in shell scripts * Special Shell Variables:: Variables you should not change * Limitations of Builtins:: Portable use of not so portable /bin/sh * Limitations of Usual Tools:: Portable use of portable tools Portable Make Programming * $< in Ordinary Make Rules:: $< in ordinary rules * Failure in Make Rules:: Failing portably in rules * Special Chars in Names:: Special Characters in Macro Names * Backslash-Newline-Newline:: Empty last lines in macro definitions * Backslash-Newline Comments:: Spanning comments across line boundaries * Long Lines in Makefiles:: Line length limitations * Macros and Submakes:: @code{make macro=value} and submakes * The Make Macro MAKEFLAGS:: @code{$(MAKEFLAGS)} portability issues * The Make Macro SHELL:: @code{$(SHELL)} portability issues * Comments in Make Rules:: Other problems with Make comments * obj/ and Make:: Don't name a subdirectory @file{obj} * make -k Status:: Exit status of @samp{make -k} * VPATH and Make:: @code{VPATH} woes * Single Suffix Rules:: Single suffix rules and separated dependencies * Timestamps and Make:: Subsecond timestamp resolution @code{VPATH} and Make * VPATH and Double-colon:: Problems with @samp{::} on ancient hosts * $< in Explicit Rules:: @code{$<} does not work in ordinary rules * Automatic Rule Rewriting:: @code{VPATH} goes wild on Solaris * Tru64 Directory Magic:: @command{mkdir} goes wild on Tru64 * Make Target Lookup:: More details about @code{VPATH} lookup Portable C and C++ Programming * Varieties of Unportability:: How to make your programs unportable * Integer Overflow:: When integers get too large * Null Pointers:: Properties of null pointers * Buffer Overruns:: Subscript errors and the like * Volatile Objects:: @code{volatile} and signals * Floating Point Portability:: Portable floating-point arithmetic * Exiting Portably:: Exiting and the exit status Manual Configuration * Specifying Names:: Specifying the system type * Canonicalizing:: Getting the canonical system type * Using System Type:: What to do with the system type Site Configuration * Help Formatting:: Customizing @samp{configure --help} * External Software:: Working with other optional software * Package Options:: Selecting optional features * Pretty Help Strings:: Formatting help string * Site Details:: Configuring site details * Transforming Names:: Changing program names when installing * Site Defaults:: Giving @command{configure} local defaults Transforming Program Names When Installing * Transformation Options:: @command{configure} options to transform names * Transformation Examples:: Sample uses of transforming names * Transformation Rules:: Makefile uses of transforming names Running @command{configure} Scripts * Basic Installation:: Instructions for typical cases * Compilers and Options:: Selecting compilers and optimization * Multiple Architectures:: Compiling for multiple architectures at once * Installation Names:: Installing in different directories * Optional Features:: Selecting optional features * System Type:: Specifying the system type * Sharing Defaults:: Setting site-wide defaults for @command{configure} * Defining Variables:: Specifying the compiler etc. * configure Invocation:: Changing how @command{configure} runs Obsolete Constructs * Obsolete config.status Use:: Different calling convention * acconfig.h:: Additional entries in @file{config.h.in} * autoupdate Invocation:: Automatic update of @file{configure.ac} * Obsolete Macros:: Backward compatibility macros * Autoconf 1:: Tips for upgrading your files * Autoconf 2.13:: Some fresher tips Upgrading From Version 1 * Changed File Names:: Files you might rename * Changed Makefiles:: New things to put in @file{Makefile.in} * Changed Macros:: Macro calls you might replace * Changed Results:: Changes in how to check test results * Changed Macro Writing:: Better ways to write your own macros Upgrading From Version 2.13 * Changed Quotation:: Broken code which used to work * New Macros:: Interaction with foreign macros * Hosts and Cross-Compilation:: Bugward compatibility kludges * AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token * AC_FOO_IFELSE vs AC_TRY_FOO:: A more generic scheme for testing sources Generating Test Suites with Autotest * Using an Autotest Test Suite:: Autotest and the user * Writing testsuite.at:: Autotest macros * testsuite Invocation:: Running @command{testsuite} scripts * Making testsuite Scripts:: Using autom4te to create @command{testsuite} Using an Autotest Test Suite * testsuite Scripts:: The concepts of Autotest * Autotest Logs:: Their contents Frequent Autoconf Questions, with answers * Distributing:: Distributing @command{configure} scripts * Why GNU M4:: Why not use the standard M4? * Bootstrapping:: Autoconf and @acronym{GNU} M4 require each other? * Why Not Imake:: Why @acronym{GNU} uses @command{configure} instead of Imake * Defining Directories:: Passing @code{datadir} to program * autom4te.cache:: What is it? Can I remove it? * Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree History of Autoconf * Genesis:: Prehistory and naming of @command{configure} * Exodus:: The plagues of M4 and Perl * Leviticus:: The priestly code of portability arrives * Numbers:: Growth and contributors * Deuteronomy:: Approaching the promises of easy configuration Copying This Manual * GNU Free Documentation License:: License for copying this manual Indices * Environment Variable Index:: Index of environment variables used * Output Variable Index:: Index of variables set in output files * Preprocessor Symbol Index:: Index of C preprocessor symbols defined * Autoconf Macro Index:: Index of Autoconf macros * M4 Macro Index:: Index of M4, M4sugar, and M4sh macros * Autotest Macro Index:: Index of Autotest macros * Program & Function Index:: Index of those with portability problems * Concept Index:: General index @end detailmenu @end menu @c ============================================================= Introduction. @node Introduction @chapter Introduction @cindex Introduction @flushright A physicist, an engineer, and a computer scientist were discussing the nature of God. ``Surely a Physicist,'' said the physicist, ``because early in the Creation, God made Light; and you know, Maxwell's equations, the dual nature of electromagnetic waves, the relativistic consequences@dots{}'' ``An Engineer!,'' said the engineer, ``because before making Light, God split the Chaos into Land and Water; it takes a hell of an engineer to handle that big amount of mud, and orderly separation of solids from liquids@dots{}'' The computer scientist shouted: ``And the Chaos, where do you think it was coming from, hmm?'' ---Anonymous @end flushright @c (via Franc,ois Pinard) Autoconf is a tool for producing shell scripts that automatically configure software source code packages to adapt to many kinds of Posix-like systems. The configuration scripts produced by Autoconf are independent of Autoconf when they are run, so their users do not need to have Autoconf. The configuration scripts produced by Autoconf require no manual user intervention when run; they do not normally even need an argument specifying the system type. Instead, they individually test for the presence of each feature that the software package they are for might need. (Before each check, they print a one-line message stating what they are checking for, so the user doesn't get too bored while waiting for the script to finish.) As a result, they deal well with systems that are hybrids or customized from the more common Posix variants. There is no need to maintain files that list the features supported by each release of each variant of Posix. For each software package that Autoconf is used with, it creates a configuration script from a template file that lists the system features that the package needs or can use. After the shell code to recognize and respond to a system feature has been written, Autoconf allows it to be shared by many software packages that can use (or need) that feature. If it later turns out that the shell code needs adjustment for some reason, it needs to be changed in only one place; all of the configuration scripts can be regenerated automatically to take advantage of the updated code. The Metaconfig package is similar in purpose to Autoconf, but the scripts it produces require manual user intervention, which is quite inconvenient when configuring large source trees. Unlike Metaconfig scripts, Autoconf scripts can support cross-compiling, if some care is taken in writing them. Autoconf does not solve all problems related to making portable software packages---for a more complete solution, it should be used in concert with other @acronym{GNU} build tools like Automake and Libtool. These other tools take on jobs like the creation of a portable, recursive makefile with all of the standard targets, linking of shared libraries, and so on. @xref{The GNU Build System}, for more information. Autoconf imposes some restrictions on the names of macros used with @code{#if} in C programs (@pxref{Preprocessor Symbol Index}). Autoconf requires @acronym{GNU} M4 in order to generate the scripts. It uses features that some versions of M4, including @acronym{GNU} M4 1.3, do not have. You should use version 1.4.7 or later of @acronym{GNU} M4. @xref{Autoconf 1}, for information about upgrading from version 1. @xref{History}, for the story of Autoconf's development. @xref{FAQ}, for answers to some common questions about Autoconf. See the @uref{http://www.gnu.org/software/autoconf/, Autoconf web page} for up-to-date information, details on the mailing lists, pointers to a list of known bugs, etc. Mail suggestions to @email{autoconf@@gnu.org, the Autoconf mailing list}. Past suggestions are @uref{http://lists.gnu.org/archive/html/autoconf/, archived}. Mail bug reports to @email{bug-autoconf@@gnu.org, the Autoconf Bugs mailing list}. Past bug reports are @uref{http://lists.gnu.org/archive/html/bug-autoconf/, archived}. If possible, first check that your bug is not already solved in current development versions, and that it has not been reported yet. Be sure to include all the needed information and a short @file{configure.ac} that demonstrates the problem. Autoconf's development tree is accessible via anonymous @acronym{CVS}; see the @uref{http://savannah.gnu.org/projects/autoconf/, Autoconf Summary} for details. Patches relative to the current @acronym{CVS} version can be sent for review to the @email{autoconf-patches@@gnu.org, Autoconf Patches mailing list}. Past patches are @uref{http://lists.gnu.org/@/archive/@/html/@/autoconf-patches/, archived}. Because of its mission, the Autoconf package itself includes only a set of often-used macros that have already demonstrated their usefulness. Nevertheless, if you wish to share your macros, or find existing ones, see the @uref{http://autoconf-archive.cryp.to/, Autoconf Macro Archive}, which is kindly run by @email{simons@@cryp.to, Peter Simons}. @c ================================================= The GNU Build System @node The GNU Build System @chapter The @acronym{GNU} Build System @cindex @acronym{GNU} build system Autoconf solves an important problem---reliable discovery of system-specific build and runtime information---but this is only one piece of the puzzle for the development of portable software. To this end, the @acronym{GNU} project has developed a suite of integrated utilities to finish the job Autoconf started: the @acronym{GNU} build system, whose most important components are Autoconf, Automake, and Libtool. In this chapter, we introduce you to those tools, point you to sources of more information, and try to convince you to use the entire @acronym{GNU} build system for your software. @menu * Automake:: Escaping makefile hell * Gnulib:: The @acronym{GNU} portability library * Libtool:: Building libraries portably * Pointers:: More info on the @acronym{GNU} build system @end menu @node Automake @section Automake The ubiquity of @command{make} means that a makefile is almost the only viable way to distribute automatic build rules for software, but one quickly runs into its numerous limitations. Its lack of support for automatic dependency tracking, recursive builds in subdirectories, reliable timestamps (e.g., for network file systems), and so on, mean that developers must painfully (and often incorrectly) reinvent the wheel for each project. Portability is non-trivial, thanks to the quirks of @command{make} on many systems. On top of all this is the manual labor required to implement the many standard targets that users have come to expect (@code{make install}, @code{make distclean}, @code{make uninstall}, etc.). Since you are, of course, using Autoconf, you also have to insert repetitive code in your @code{Makefile.in} to recognize @code{@@CC@@}, @code{@@CFLAGS@@}, and other substitutions provided by @command{configure}. Into this mess steps @dfn{Automake}. @cindex Automake Automake allows you to specify your build needs in a @code{Makefile.am} file with a vastly simpler and more powerful syntax than that of a plain makefile, and then generates a portable @code{Makefile.in} for use with Autoconf. For example, the @code{Makefile.am} to build and install a simple ``Hello world'' program might look like: @example bin_PROGRAMS = hello hello_SOURCES = hello.c @end example @noindent The resulting @code{Makefile.in} (~400 lines) automatically supports all the standard targets, the substitutions provided by Autoconf, automatic dependency tracking, @code{VPATH} building, and so on. @command{make} builds the @code{hello} program, and @code{make install} installs it in @file{/usr/local/bin} (or whatever prefix was given to @command{configure}, if not @file{/usr/local}). The benefits of Automake increase for larger packages (especially ones with subdirectories), but even for small programs the added convenience and portability can be substantial. And that's not all@enddots{} @node Gnulib @section Gnulib @acronym{GNU} software has a well-deserved reputation for running on many different types of systems. While our primary goal is to write software for the @acronym{GNU} system, many users and developers have been introduced to us through the systems that they were already using. @cindex Gnulib Gnulib is a central location for common @acronym{GNU} code, intended to be shared among free software packages. Its components are typically shared at the source level, rather than being a library that gets built, installed, and linked against. The idea is to copy files from Gnulib into your own source tree. There is no distribution tarball; developers should just grab source modules from the repository. The source files are available online, under various licenses, mostly @acronym{GNU} @acronym{GPL} or @acronym{GNU} @acronym{LGPL}. Gnulib modules typically contain C source code along with Autoconf macros used to configure the source code. For example, the Gnulib @code{stdbool} module implements a @file{stdbool.h} header that nearly conforms to C99, even on old-fashioned hosts that lack @file{stdbool.h}. This module contains a source file for the replacement header, along with an Autoconf macro that arranges to use the replacement header on old-fashioned systems. @node Libtool @section Libtool Often, one wants to build not only programs, but libraries, so that other programs can benefit from the fruits of your labor. Ideally, one would like to produce @emph{shared} (dynamically linked) libraries, which can be used by multiple programs without duplication on disk or in memory and can be updated independently of the linked programs. Producing shared libraries portably, however, is the stuff of nightmares---each system has its own incompatible tools, compiler flags, and magic incantations. Fortunately, @acronym{GNU} provides a solution: @dfn{Libtool}. @cindex Libtool Libtool handles all the requirements of building shared libraries for you, and at this time seems to be the @emph{only} way to do so with any portability. It also handles many other headaches, such as: the interaction of Make rules with the variable suffixes of shared libraries, linking reliably with shared libraries before they are installed by the superuser, and supplying a consistent versioning system (so that different versions of a library can be installed or upgraded without breaking binary compatibility). Although Libtool, like Autoconf, can be used without Automake, it is most simply utilized in conjunction with Automake---there, Libtool is used automatically whenever shared libraries are needed, and you need not know its syntax. @node Pointers @section Pointers Developers who are used to the simplicity of @command{make} for small projects on a single system might be daunted at the prospect of learning to use Automake and Autoconf. As your software is distributed to more and more users, however, you otherwise quickly find yourself putting lots of effort into reinventing the services that the @acronym{GNU} build tools provide, and making the same mistakes that they once made and overcame. (Besides, since you're already learning Autoconf, Automake is a piece of cake.) There are a number of places that you can go to for more information on the @acronym{GNU} build tools. @itemize @minus @item Web The home pages for @uref{http://www.gnu.org/@/software/@/autoconf/, Autoconf}, @uref{http://www.gnu.org/@/software/@/automake/, Automake}, @uref{http://www.gnu.org/@/software/@/gnulib/, Gnulib}, and @uref{http://www.gnu.org/@/software/@/libtool/, Libtool}. @item Automake Manual @xref{Top, , Automake, automake, @acronym{GNU} Automake}, for more information on Automake. @item Books The book @cite{@acronym{GNU} Autoconf, Automake and Libtool}@footnote{@cite{@acronym{GNU} Autoconf, Automake and Libtool}, by G. V. Vaughan, B. Elliston, T. Tromey, and I. L. Taylor. SAMS (originally New Riders), 2000, ISBN 1578701902.} describes the complete @acronym{GNU} build environment. You can also find @uref{http://sources.redhat.com/@/autobook/, the entire book on-line}. @end itemize @c ================================================= Making configure Scripts. @node Making configure Scripts @chapter Making @command{configure} Scripts @cindex @file{aclocal.m4} @cindex @command{configure} The configuration scripts that Autoconf produces are by convention called @command{configure}. When run, @command{configure} creates several files, replacing configuration parameters in them with appropriate values. The files that @command{configure} creates are: @itemize @minus @item one or more @file{Makefile} files, usually one in each subdirectory of the package (@pxref{Makefile Substitutions}); @item optionally, a C header file, the name of which is configurable, containing @code{#define} directives (@pxref{Configuration Headers}); @item a shell script called @file{config.status} that, when run, recreates the files listed above (@pxref{config.status Invocation}); @item an optional shell script normally called @file{config.cache} (created when using @samp{configure --config-cache}) that saves the results of running many of the tests (@pxref{Cache Files}); @item a file called @file{config.log} containing any messages produced by compilers, to help debugging if @command{configure} makes a mistake. @end itemize @cindex @file{configure.in} @cindex @file{configure.ac} To create a @command{configure} script with Autoconf, you need to write an Autoconf input file @file{configure.ac} (or @file{configure.in}) and run @command{autoconf} on it. If you write your own feature tests to supplement those that come with Autoconf, you might also write files called @file{aclocal.m4} and @file{acsite.m4}. If you use a C header file to contain @code{#define} directives, you might also run @command{autoheader}, and you can distribute the generated file @file{config.h.in} with the package. Here is a diagram showing how the files that can be used in configuration are produced. Programs that are executed are suffixed by @samp{*}. Optional files are enclosed in square brackets (@samp{[]}). @command{autoconf} and @command{autoheader} also read the installed Autoconf macro files (by reading @file{autoconf.m4}). @noindent Files used in preparing a software package for distribution: @example your source files --> [autoscan*] --> [configure.scan] --> configure.ac @group configure.ac --. | .------> autoconf* -----> configure [aclocal.m4] --+---+ | `-----> [autoheader*] --> [config.h.in] [acsite.m4] ---' @end group Makefile.in -------------------------------> Makefile.in @end example @noindent Files used in configuring a software package: @example @group .-------------> [config.cache] configure* ------------+-------------> config.log | [config.h.in] -. v .-> [config.h] -. +--> config.status* -+ +--> make* Makefile.in ---' `-> Makefile ---' @end group @end example @menu * Writing configure.ac:: What to put in an Autoconf input file * autoscan Invocation:: Semi-automatic @file{configure.ac} writing * ifnames Invocation:: Listing the conditionals in source code * autoconf Invocation:: How to create configuration scripts * autoreconf Invocation:: Remaking multiple @command{configure} scripts @end menu @node Writing configure.ac @section Writing @file{configure.ac} To produce a @command{configure} script for a software package, create a file called @file{configure.ac} that contains invocations of the Autoconf macros that test the system features your package needs or can use. Autoconf macros already exist to check for many features; see @ref{Existing Tests}, for their descriptions. For most other features, you can use Autoconf template macros to produce custom checks; see @ref{Writing Tests}, for information about them. For especially tricky or specialized features, @file{configure.ac} might need to contain some hand-crafted shell commands; see @ref{Portable Shell}. The @command{autoscan} program can give you a good start in writing @file{configure.ac} (@pxref{autoscan Invocation}, for more information). Previous versions of Autoconf promoted the name @file{configure.in}, which is somewhat ambiguous (the tool needed to process this file is not described by its extension), and introduces a slight confusion with @file{config.h.in} and so on (for which @samp{.in} means ``to be processed by @command{configure}''). Using @file{configure.ac} is now preferred. @menu * Shell Script Compiler:: Autoconf as solution of a problem * Autoconf Language:: Programming in Autoconf * configure.ac Layout:: Standard organization of @file{configure.ac} @end menu @node Shell Script Compiler @subsection A Shell Script Compiler Just as for any other computer language, in order to properly program @file{configure.ac} in Autoconf you must understand @emph{what} problem the language tries to address and @emph{how} it does so. The problem Autoconf addresses is that the world is a mess. After all, you are using Autoconf in order to have your package compile easily on all sorts of different systems, some of them being extremely hostile. Autoconf itself bears the price for these differences: @command{configure} must run on all those systems, and thus @command{configure} must limit itself to their lowest common denominator of features. Naturally, you might then think of shell scripts; who needs @command{autoconf}? A set of properly written shell functions is enough to make it easy to write @command{configure} scripts by hand. Sigh! Unfortunately, shell functions do not belong to the least common denominator; therefore, where you would like to define a function and use it ten times, you would instead need to copy its body ten times. So, what is really needed is some kind of compiler, @command{autoconf}, that takes an Autoconf program, @file{configure.ac}, and transforms it into a portable shell script, @command{configure}. How does @command{autoconf} perform this task? There are two obvious possibilities: creating a brand new language or extending an existing one. The former option is attractive: all sorts of optimizations could easily be implemented in the compiler and many rigorous checks could be performed on the Autoconf program (e.g., rejecting any non-portable construct). Alternatively, you can extend an existing language, such as the @code{sh} (Bourne shell) language. Autoconf does the latter: it is a layer on top of @code{sh}. It was therefore most convenient to implement @command{autoconf} as a macro expander: a program that repeatedly performs @dfn{macro expansions} on text input, replacing macro calls with macro bodies and producing a pure @code{sh} script in the end. Instead of implementing a dedicated Autoconf macro expander, it is natural to use an existing general-purpose macro language, such as M4, and implement the extensions as a set of M4 macros. @node Autoconf Language @subsection The Autoconf Language @cindex quotation The Autoconf language differs from many other computer languages because it treats actual code the same as plain text. Whereas in C, for instance, data and instructions have different syntactic status, in Autoconf their status is rigorously the same. Therefore, we need a means to distinguish literal strings from text to be expanded: quotation. When calling macros that take arguments, there must not be any white space between the macro name and the open parenthesis. Arguments should be enclosed within the M4 quote characters @samp{[} and @samp{]}, and be separated by commas. Any leading blanks or newlines in arguments are ignored, unless they are quoted. You should always quote an argument that might contain a macro name, comma, parenthesis, or a leading blank or newline. This rule applies recursively for every macro call, including macros called from other macros. For instance: @example AC_CHECK_HEADER([stdio.h], [AC_DEFINE([HAVE_STDIO_H], [1], [Define to 1 if you have .])], [AC_MSG_ERROR([Sorry, can't do anything for you])]) @end example @noindent is quoted properly. You may safely simplify its quotation to: @example AC_CHECK_HEADER([stdio.h], [AC_DEFINE([HAVE_STDIO_H], 1, [Define to 1 if you have .])], [AC_MSG_ERROR([Sorry, can't do anything for you])]) @end example @noindent because @samp{1} cannot contain a macro call. Here, the argument of @code{AC_MSG_ERROR} must be quoted; otherwise, its comma would be interpreted as an argument separator. Also, the second and third arguments of @samp{AC_CHECK_HEADER} must be quoted, since they contain macro calls. The three arguments @samp{HAVE_STDIO_H}, @samp{stdio.h}, and @samp{Define to 1 if you have .} do not need quoting, but if you unwisely defined a macro with a name like @samp{Define} or @samp{stdio} then they would need quoting. Cautious Autoconf users would keep the quotes, but many Autoconf users find such precautions annoying, and would rewrite the example as follows: @example AC_CHECK_HEADER(stdio.h, [AC_DEFINE(HAVE_STDIO_H, 1, [Define to 1 if you have .])], [AC_MSG_ERROR([Sorry, can't do anything for you])]) @end example @noindent This is safe, so long as you adopt good naming conventions and do not define macros with names like @samp{HAVE_STDIO_H}, @samp{stdio}, or @samp{h}. Though it is also safe here to omit the quotes around @samp{Define to 1 if you have .} this is not recommended, as message strings are more likely to inadvertently contain commas. The following example is wrong and dangerous, as it is underquoted: @example AC_CHECK_HEADER(stdio.h, AC_DEFINE(HAVE_STDIO_H, 1, Define to 1 if you have .), AC_MSG_ERROR([Sorry, can't do anything for you])) @end example In other cases, you may have to use text that also resembles a macro call. You must quote that text even when it is not passed as a macro argument: @example echo "Hard rock was here! --[AC_DC]" @end example @noindent which results in: @example echo "Hard rock was here! --AC_DC" @end example @noindent When you use the same text in a macro argument, you must therefore have an extra quotation level (since one is stripped away by the macro substitution). In general, then, it is a good idea to @emph{use double quoting for all literal string arguments}: @example AC_MSG_WARN([[AC_DC stinks --Iron Maiden]]) @end example You are now able to understand one of the constructs of Autoconf that has been continually misunderstood@dots{} The rule of thumb is that @emph{whenever you expect macro expansion, expect quote expansion}; i.e., expect one level of quotes to be lost. For instance: @example AC_COMPILE_IFELSE([char b[10];], [], [AC_MSG_ERROR([you lose])]) @end example @noindent is incorrect: here, the first argument of @code{AC_COMPILE_IFELSE} is @samp{char b[10];} and is expanded once, which results in @samp{char b10;}. (There was an idiom common in Autoconf's past to address this issue via the M4 @code{changequote} primitive, but do not use it!) Let's take a closer look: the author meant the first argument to be understood as a literal, and therefore it must be quoted twice: @example AC_COMPILE_IFELSE([[char b[10];]], [], [AC_MSG_ERROR([you lose])]) @end example @noindent Voil@`a, you actually produce @samp{char b[10];} this time! On the other hand, descriptions (e.g., the last parameter of @code{AC_DEFINE} or @code{AS_HELP_STRING}) are not literals---they are subject to line breaking, for example---and should not be double quoted. Even if these descriptions are short and are not actually broken, double quoting them yields weird results. Some macros take optional arguments, which this documentation represents as @ovar{arg} (not to be confused with the quote characters). You may just leave them empty, or use @samp{[]} to make the emptiness of the argument explicit, or you may simply omit the trailing commas. The three lines below are equivalent: @example AC_CHECK_HEADERS([stdio.h], [], [], []) AC_CHECK_HEADERS([stdio.h],,,) AC_CHECK_HEADERS([stdio.h]) @end example It is best to put each macro call on its own line in @file{configure.ac}. Most of the macros don't add extra newlines; they rely on the newline after the macro call to terminate the commands. This approach makes the generated @command{configure} script a little easier to read by not inserting lots of blank lines. It is generally safe to set shell variables on the same line as a macro call, because the shell allows assignments without intervening newlines. You can include comments in @file{configure.ac} files by starting them with the @samp{#}. For example, it is helpful to begin @file{configure.ac} files with a line like this: @example # Process this file with autoconf to produce a configure script. @end example @node configure.ac Layout @subsection Standard @file{configure.ac} Layout The order in which @file{configure.ac} calls the Autoconf macros is not important, with a few exceptions. Every @file{configure.ac} must contain a call to @code{AC_INIT} before the checks, and a call to @code{AC_OUTPUT} at the end (@pxref{Output}). Additionally, some macros rely on other macros having been called first, because they check previously set values of some variables to decide what to do. These macros are noted in the individual descriptions (@pxref{Existing Tests}), and they also warn you when @command{configure} is created if they are called out of order. To encourage consistency, here is a suggested order for calling the Autoconf macros. Generally speaking, the things near the end of this list are those that could depend on things earlier in it. For example, library functions could be affected by types and libraries. @display @group Autoconf requirements @code{AC_INIT(@var{package}, @var{version}, @var{bug-report-address})} information on the package checks for programs checks for libraries checks for header files checks for types checks for structures checks for compiler characteristics checks for library functions checks for system services @code{AC_CONFIG_FILES(@r{[}@var{file@dots{}}@r{]})} @code{AC_OUTPUT} @end group @end display @node autoscan Invocation @section Using @command{autoscan} to Create @file{configure.ac} @cindex @command{autoscan} The @command{autoscan} program can help you create and/or maintain a @file{configure.ac} file for a software package. @command{autoscan} examines source files in the directory tree rooted at a directory given as a command line argument, or the current directory if none is given. It searches the source files for common portability problems and creates a file @file{configure.scan} which is a preliminary @file{configure.ac} for that package, and checks a possibly existing @file{configure.ac} for completeness. When using @command{autoscan} to create a @file{configure.ac}, you should manually examine @file{configure.scan} before renaming it to @file{configure.ac}; it probably needs some adjustments. Occasionally, @command{autoscan} outputs a macro in the wrong order relative to another macro, so that @command{autoconf} produces a warning; you need to move such macros manually. Also, if you want the package to use a configuration header file, you must add a call to @code{AC_CONFIG_HEADERS} (@pxref{Configuration Headers}). You might also have to change or add some @code{#if} directives to your program in order to make it work with Autoconf (@pxref{ifnames Invocation}, for information about a program that can help with that job). When using @command{autoscan} to maintain a @file{configure.ac}, simply consider adding its suggestions. The file @file{autoscan.log} contains detailed information on why a macro is requested. @command{autoscan} uses several data files (installed along with Autoconf) to determine which macros to output when it finds particular symbols in a package's source files. These data files all have the same format: each line consists of a symbol, one or more blanks, and the Autoconf macro to output if that symbol is encountered. Lines starting with @samp{#} are comments. @command{autoscan} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Print the names of the files it examines and the potentially interesting symbols it finds in them. This output can be voluminous. @item --include=@var{dir} @itemx -I @var{dir} Append @var{dir} to the include path. Multiple invocations accumulate. @item --prepend-include=@var{dir} @item -B @var{dir} Prepend @var{dir} to the include path. Multiple invocations accumulate. @end table @node ifnames Invocation @section Using @command{ifnames} to List Conditionals @cindex @command{ifnames} @command{ifnames} can help you write @file{configure.ac} for a software package. It prints the identifiers that the package already uses in C preprocessor conditionals. If a package has already been set up to have some portability, @command{ifnames} can thus help you figure out what its @command{configure} needs to check for. It may help fill in some gaps in a @file{configure.ac} generated by @command{autoscan} (@pxref{autoscan Invocation}). @command{ifnames} scans all of the C source files named on the command line (or the standard input, if none are given) and writes to the standard output a sorted list of all the identifiers that appear in those files in @code{#if}, @code{#elif}, @code{#ifdef}, or @code{#ifndef} directives. It prints each identifier on a line, followed by a space-separated list of the files in which that identifier occurs. @noindent @command{ifnames} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @end table @node autoconf Invocation @section Using @command{autoconf} to Create @command{configure} @cindex @command{autoconf} To create @command{configure} from @file{configure.ac}, run the @command{autoconf} program with no arguments. @command{autoconf} processes @file{configure.ac} with the M4 macro processor, using the Autoconf macros. If you give @command{autoconf} an argument, it reads that file instead of @file{configure.ac} and writes the configuration script to the standard output instead of to @command{configure}. If you give @command{autoconf} the argument @option{-}, it reads from the standard input instead of @file{configure.ac} and writes the configuration script to the standard output. The Autoconf macros are defined in several files. Some of the files are distributed with Autoconf; @command{autoconf} reads them first. Then it looks for the optional file @file{acsite.m4} in the directory that contains the distributed Autoconf macro files, and for the optional file @file{aclocal.m4} in the current directory. Those files can contain your site's or the package's own Autoconf macro definitions (@pxref{Writing Autoconf Macros}, for more information). If a macro is defined in more than one of the files that @command{autoconf} reads, the last definition it reads overrides the earlier ones. @command{autoconf} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Report processing steps. @item --debug @itemx -d Don't remove the temporary files. @item --force @itemx -f Remake @file{configure} even if newer than its input files. @item --include=@var{dir} @itemx -I @var{dir} Append @var{dir} to the include path. Multiple invocations accumulate. @item --prepend-include=@var{dir} @item -B @var{dir} Prepend @var{dir} to the include path. Multiple invocations accumulate. @item --output=@var{file} @itemx -o @var{file} Save output (script or trace) to @var{file}. The file @option{-} stands for the standard output. @item --warnings=@var{category} @itemx -W @var{category} @evindex WARNINGS Report the warnings related to @var{category} (which can actually be a comma separated list). @xref{Reporting Messages}, macro @code{AC_DIAGNOSE}, for a comprehensive list of categories. Special values include: @table @samp @item all report all the warnings @item none report none @item error treats warnings as errors @item no-@var{category} disable warnings falling into @var{category} @end table Warnings about @samp{syntax} are enabled by default, and the environment variable @env{WARNINGS}, a comma separated list of categories, is honored as well. Passing @option{-W @var{category}} actually behaves as if you had passed @option{--warnings=syntax,$WARNINGS,@var{category}}. If you want to disable the defaults and @env{WARNINGS}, but (for example) enable the warnings about obsolete constructs, you would use @option{-W none,obsolete}. @cindex Back trace @cindex Macro invocation stack Because @command{autoconf} uses @command{autom4te} behind the scenes, it displays a back trace for errors, but not for warnings; if you want them, just pass @option{-W error}. @xref{autom4te Invocation}, for some examples. @item --trace=@var{macro}[:@var{format}] @itemx -t @var{macro}[:@var{format}] Do not create the @command{configure} script, but list the calls to @var{macro} according to the @var{format}. Multiple @option{--trace} arguments can be used to list several macros. Multiple @option{--trace} arguments for a single macro are not cumulative; instead, you should just make @var{format} as long as needed. The @var{format} is a regular string, with newlines if desired, and several special escape codes. It defaults to @samp{$f:$l:$n:$%}; see @ref{autom4te Invocation}, for details on the @var{format}. @item --initialization @itemx -i By default, @option{--trace} does not trace the initialization of the Autoconf macros (typically the @code{AC_DEFUN} definitions). This results in a noticeable speedup, but can be disabled by this option. @end table It is often necessary to check the content of a @file{configure.ac} file, but parsing it yourself is extremely fragile and error-prone. It is suggested that you rely upon @option{--trace} to scan @file{configure.ac}. For instance, to find the list of variables that are substituted, use: @example @group $ @kbd{autoconf -t AC_SUBST} configure.ac:2:AC_SUBST:ECHO_C configure.ac:2:AC_SUBST:ECHO_N configure.ac:2:AC_SUBST:ECHO_T @i{More traces deleted} @end group @end example @noindent The example below highlights the difference between @samp{$@@}, @samp{$*}, and @samp{$%}. @example @group $ @kbd{cat configure.ac} AC_DEFINE(This, is, [an [example]]) $ @kbd{autoconf -t 'AC_DEFINE:@@: $@@} *: $* %: $%' @@: [This],[is],[an [example]] *: This,is,an [example] %: This:is:an [example] @end group @end example @noindent The @var{format} gives you a lot of freedom: @example @group $ @kbd{autoconf -t 'AC_SUBST:$$ac_subst@{"$1"@} = "$f:$l";'} $ac_subst@{"ECHO_C"@} = "configure.ac:2"; $ac_subst@{"ECHO_N"@} = "configure.ac:2"; $ac_subst@{"ECHO_T"@} = "configure.ac:2"; @i{More traces deleted} @end group @end example @noindent A long @var{separator} can be used to improve the readability of complex structures, and to ease their parsing (for instance when no single character is suitable as a separator): @example @group $ @kbd{autoconf -t 'AM_MISSING_PROG:$@{|:::::|@}*'} ACLOCAL|:::::|aclocal|:::::|$missing_dir AUTOCONF|:::::|autoconf|:::::|$missing_dir AUTOMAKE|:::::|automake|:::::|$missing_dir @i{More traces deleted} @end group @end example @node autoreconf Invocation @section Using @command{autoreconf} to Update @command{configure} Scripts @cindex @command{autoreconf} Installing the various components of the @acronym{GNU} Build System can be tedious: running @command{autopoint} for Gettext, @command{automake} for @file{Makefile.in} etc.@: in each directory. It may be needed either because some tools such as @command{automake} have been updated on your system, or because some of the sources such as @file{configure.ac} have been updated, or finally, simply in order to install the @acronym{GNU} Build System in a fresh tree. @command{autoreconf} runs @command{autoconf}, @command{autoheader}, @command{aclocal}, @command{automake}, @command{libtoolize}, and @command{autopoint} (when appropriate) repeatedly to update the @acronym{GNU} Build System in the specified directories and their subdirectories (@pxref{Subdirectories}). By default, it only remakes those files that are older than their sources. If you install a new version of some tool, you can make @command{autoreconf} remake @emph{all} of the files by giving it the @option{--force} option. @xref{Automatic Remaking}, for Make rules to automatically remake @command{configure} scripts when their source files change. That method handles the timestamps of configuration header templates properly, but does not pass @option{--autoconf-dir=@var{dir}} or @option{--localdir=@var{dir}}. @cindex Gettext @cindex @command{autopoint} Gettext supplies the @command{autopoint} command to add translation infrastructure to a source package. If you use @command{autopoint}, your @file{configure.ac} should invoke both @code{AM_GNU_GETTEXT} and @code{AM_GNU_GETTEXT_VERSION(@var{gettext-version})}. @xref{autopoint Invocation, , Invoking the @code{autopoint} Program, gettext, @acronym{GNU} @code{gettext} utilities}, for further details. @noindent @command{autoreconf} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose Print the name of each directory @command{autoreconf} examines and the commands it runs. If given two or more times, pass @option{--verbose} to subordinate tools that support it. @item --debug @itemx -d Don't remove the temporary files. @item --force @itemx -f Remake even @file{configure} scripts and configuration headers that are newer than their input files (@file{configure.ac} and, if present, @file{aclocal.m4}). @item --install @itemx -i Install the missing auxiliary files in the package. By default, files are copied; this can be changed with @option{--symlink}. If deemed appropriate, this option triggers calls to @samp{automake --add-missing}, @samp{libtoolize}, @samp{autopoint}, etc. @item --no-recursive Do not rebuild files in subdirectories to configure (see @ref{Subdirectories}, macro @code{AC_CONFIG_SUBDIRS}). @item --symlink @itemx -s When used with @option{--install}, install symbolic links to the missing auxiliary files instead of copying them. @item --make @itemx -m When the directories were configured, update the configuration by running @samp{./config.status --recheck && ./config.status}, and then run @samp{make}. @item --include=@var{dir} @itemx -I @var{dir} Append @var{dir} to the include path. Multiple invocations accumulate. Passed on to @command{autoconf} and @command{autoheader} internally. @item --prepend-include=@var{dir} @item -B @var{dir} Prepend @var{dir} to the include path. Multiple invocations accumulate. Passed on to @command{autoconf} and @command{autoheader} internally. @item --warnings=@var{category} @itemx -W @var{category} @evindex WARNINGS Report the warnings related to @var{category} (which can actually be a comma separated list). @table @samp @item cross related to cross compilation issues. @item obsolete report the uses of obsolete constructs. @item portability portability issues @item syntax dubious syntactic constructs. @item all report all the warnings @item none report none @item error treats warnings as errors @item no-@var{category} disable warnings falling into @var{category} @end table Warnings about @samp{syntax} are enabled by default, and the environment variable @env{WARNINGS}, a comma separated list of categories, is honored as well. Passing @option{-W @var{category}} actually behaves as if you had passed @option{--warnings=syntax,$WARNINGS,@var{category}}. If you want to disable the defaults and @env{WARNINGS}, but (for example) enable the warnings about obsolete constructs, you would use @option{-W none,obsolete}. @end table If you want @command{autoreconf} to pass flags that are not listed here on to @command{aclocal}, set @code{ACLOCAL_AMFLAGS} in your @file{Makefile.am}. @c ========================================= Initialization and Output Files. @node Setup @chapter Initialization and Output Files Autoconf-generated @command{configure} scripts need some information about how to initialize, such as how to find the package's source files and about the output files to produce. The following sections describe the initialization and the creation of output files. @menu * Initializing configure:: Option processing etc. * Notices:: Copyright, version numbers in @command{configure} * Input:: Where Autoconf should find files * Output:: Outputting results from the configuration * Configuration Actions:: Preparing the output based on results * Configuration Files:: Creating output files * Makefile Substitutions:: Using output variables in makefiles * Configuration Headers:: Creating a configuration header file * Configuration Commands:: Running arbitrary instantiation commands * Configuration Links:: Links depending on the configuration * Subdirectories:: Configuring independent packages together * Default Prefix:: Changing the default installation prefix @end menu @node Initializing configure @section Initializing @command{configure} Every @command{configure} script must call @code{AC_INIT} before doing anything else. The only other required macro is @code{AC_OUTPUT} (@pxref{Output}). @defmac AC_INIT (@var{package}, @var{version}, @ovar{bug-report}, @ovar{tarname}) @acindex{INIT} Process any command-line arguments and perform various initializations and verifications. Set the name of the @var{package} and its @var{version}. These are typically used in @option{--version} support, including that of @command{configure}. The optional argument @var{bug-report} should be the email to which users should send bug reports. The package @var{tarname} differs from @var{package}: the latter designates the full package name (e.g., @samp{GNU Autoconf}), while the former is meant for distribution tar ball names (e.g., @samp{autoconf}). It defaults to @var{package} with @samp{GNU } stripped, lower-cased, and all characters other than alphanumerics and underscores are changed to @samp{-}. It is preferable that the arguments of @code{AC_INIT} be static, i.e., there should not be any shell computation, but they can be computed by M4. The following M4 macros (e.g., @code{AC_PACKAGE_NAME}), output variables (e.g., @code{PACKAGE_NAME}), and preprocessor symbols (e.g., @code{PACKAGE_NAME}) are defined by @code{AC_INIT}: @table @asis @item @code{AC_PACKAGE_NAME}, @code{PACKAGE_NAME} @acindex{PACKAGE_NAME} @ovindex PACKAGE_NAME @cvindex PACKAGE_NAME Exactly @var{package}. @item @code{AC_PACKAGE_TARNAME}, @code{PACKAGE_TARNAME} @acindex{PACKAGE_TARNAME} @ovindex PACKAGE_TARNAME @cvindex PACKAGE_TARNAME Exactly @var{tarname}. @item @code{AC_PACKAGE_VERSION}, @code{PACKAGE_VERSION} @acindex{PACKAGE_VERSION} @ovindex PACKAGE_VERSION @cvindex PACKAGE_VERSION Exactly @var{version}. @item @code{AC_PACKAGE_STRING}, @code{PACKAGE_STRING} @acindex{PACKAGE_STRING} @ovindex PACKAGE_STRING @cvindex PACKAGE_STRING Exactly @samp{@var{package} @var{version}}. @item @code{AC_PACKAGE_BUGREPORT}, @code{PACKAGE_BUGREPORT} @acindex{PACKAGE_BUGREPORT} @ovindex PACKAGE_BUGREPORT @cvindex PACKAGE_BUGREPORT Exactly @var{bug-report}. @end table @end defmac If your @command{configure} script does its own option processing, it should inspect @samp{$@@} or @samp{$*} immediately after calling @code{AC_INIT}, because other Autoconf macros liberally use the @command{set} command to process strings, and this has the side effect of updating @samp{$@@} and @samp{$*}. However, we suggest that you use standard macros like @code{AC_ARG_ENABLE} instead of attempting to implement your own option processing. @xref{Site Configuration}. @node Notices @section Notices in @command{configure} @cindex Notices in @command{configure} The following macros manage version numbers for @command{configure} scripts. Using them is optional. @c FIXME: AC_PREREQ should not be here @defmac AC_PREREQ (@var{version}) @acindex{PREREQ} @cindex Version Ensure that a recent enough version of Autoconf is being used. If the version of Autoconf being used to create @command{configure} is earlier than @var{version}, print an error message to the standard error output and exit with failure (exit status is 63). For example: @example AC_PREREQ([@value{VERSION}]) @end example This macro is the only macro that may be used before @code{AC_INIT}, but for consistency, you are invited not to do so. @end defmac @defmac AC_COPYRIGHT (@var{copyright-notice}) @acindex{COPYRIGHT} @cindex Copyright Notice State that, in addition to the Free Software Foundation's copyright on the Autoconf macros, parts of your @command{configure} are covered by the @var{copyright-notice}. The @var{copyright-notice} shows up in both the head of @command{configure} and in @samp{configure --version}. @end defmac @defmac AC_REVISION (@var{revision-info}) @acindex{REVISION} @cindex Revision Copy revision stamp @var{revision-info} into the @command{configure} script, with any dollar signs or double-quotes removed. This macro lets you put a revision stamp from @file{configure.ac} into @command{configure} without @acronym{RCS} or @acronym{CVS} changing it when you check in @command{configure}. That way, you can determine easily which revision of @file{configure.ac} a particular @command{configure} corresponds to. For example, this line in @file{configure.ac}: @c The asis prevents RCS from changing the example in the manual. @example AC_REVISION([$@asis{Revision: 1.30 }$]) @end example @noindent produces this in @command{configure}: @example #!/bin/sh # From configure.ac Revision: 1.30 @end example @end defmac @node Input @section Finding @command{configure} Input @defmac AC_CONFIG_SRCDIR (@var{unique-file-in-source-dir}) @acindex{CONFIG_SRCDIR} @var{unique-file-in-source-dir} is some file that is in the package's source directory; @command{configure} checks for this file's existence to make sure that the directory that it is told contains the source code in fact does. Occasionally people accidentally specify the wrong directory with @option{--srcdir}; this is a safety check. @xref{configure Invocation}, for more information. @end defmac @c FIXME: Remove definitively once --install explained. @c @c Small packages may store all their macros in @code{aclocal.m4}. As the @c set of macros grows, or for maintenance reasons, a maintainer may prefer @c to split the macros in several files. In this case, Autoconf must be @c told which files to load, and in which order. @c @c @defmac AC_INCLUDE (@var{file}@dots{}) @c @acindex{INCLUDE} @c @c FIXME: There is no longer shell globbing. @c Read the macro definitions that appear in the listed files. A list of @c space-separated file names or shell globbing patterns is expected. The @c files are read in the order they're listed. @c @c Because the order of definition of macros is important (only the last @c definition of a macro is used), beware that it is @code{AC_INIT} that @c loads @file{acsite.m4} and @file{aclocal.m4}. Note that @c @code{AC_INCLUDE}ing a file before @code{AC_INIT} or within @c @file{aclocal.m4} is different from doing so after @code{AC_INIT}: in @c the latter case, non-macro lines from included files may end up in the @c @file{configure} script, whereas in the former case, they'd be discarded @c just like any text that appear before @code{AC_INIT}. @c @end defmac Packages that do manual configuration or use the @command{install} program might need to tell @command{configure} where to find some other shell scripts by calling @code{AC_CONFIG_AUX_DIR}, though the default places it looks are correct for most cases. @defmac AC_CONFIG_AUX_DIR (@var{dir}) @acindex{CONFIG_AUX_DIR} Use the auxiliary build tools (e.g., @file{install-sh}, @file{config.sub}, @file{config.guess}, Cygnus @command{configure}, Automake and Libtool scripts, etc.)@: that are in directory @var{dir}. These are auxiliary files used in configuration. @var{dir} can be either absolute or relative to @file{@var{srcdir}}. The default is @file{@var{srcdir}} or @file{@var{srcdir}/..} or @file{@var{srcdir}/../..}, whichever is the first that contains @file{install-sh}. The other files are not checked for, so that using @code{AC_PROG_INSTALL} does not automatically require distributing the other auxiliary files. It checks for @file{install.sh} also, but that name is obsolete because some @code{make} have a rule that creates @file{install} from it if there is no makefile. The auxiliary directory is commonly named @file{build-aux}. If you need portability to @acronym{DOS} variants, do not name the auxiliary directory @file{aux}. @xref{File System Conventions}. @end defmac @defmac AC_REQUIRE_AUX_FILE (@var{file}) @acindex{REQUIRE_AUX_FILE} Declares that @var{file} is expected in the directory defined above. In Autoconf proper, this macro does nothing: its sole purpose is to be traced by third-party tools to produce a list of expected auxiliary files. For instance it is called by macros like @code{AC_PROG_INSTALL} (@pxref{Particular Programs}) or @code{AC_CANONICAL_BUILD} (@pxref{Canonicalizing}) to register the auxiliary files they need. @end defmac Similarly, packages that use @command{aclocal} should declare where local macros can be found using @code{AC_CONFIG_MACRO_DIR}. @defmac AC_CONFIG_MACRO_DIR (@var{dir}) @acindex{CONFIG_MACRO_DIR} Specify @var{dir} as the location of additional local Autoconf macros. This macro is intended for use by future versions of commands like @command{autoreconf} that trace macro calls. It should be called directly from @file{configure.ac} so that tools that install macros for @command{aclocal} can find the macros' declarations. @end defmac @node Output @section Outputting Files @cindex Outputting files Every Autoconf script, e.g., @file{configure.ac}, should finish by calling @code{AC_OUTPUT}. That is the macro that generates and runs @file{config.status}, which in turn creates the makefiles and any other files resulting from configuration. This is the only required macro besides @code{AC_INIT} (@pxref{Input}). @defmac AC_OUTPUT @acindex{OUTPUT} @cindex Instantiation Generate @file{config.status} and launch it. Call this macro once, at the end of @file{configure.ac}. @file{config.status} performs all the configuration actions: all the output files (see @ref{Configuration Files}, macro @code{AC_CONFIG_FILES}), header files (see @ref{Configuration Headers}, macro @code{AC_CONFIG_HEADERS}), commands (see @ref{Configuration Commands}, macro @code{AC_CONFIG_COMMANDS}), links (see @ref{Configuration Links}, macro @code{AC_CONFIG_LINKS}), subdirectories to configure (see @ref{Subdirectories}, macro @code{AC_CONFIG_SUBDIRS}) are honored. The location of your @code{AC_OUTPUT} invocation is the exact point where configuration actions are taken: any code afterwards is executed by @code{configure} once @command{config.status} was run. If you want to bind actions to @command{config.status} itself (independently of whether @command{configure} is being run), see @ref{Configuration Commands, , Running Arbitrary Configuration Commands}. @end defmac Historically, the usage of @code{AC_OUTPUT} was somewhat different. @xref{Obsolete Macros}, for a description of the arguments that @code{AC_OUTPUT} used to support. If you run @command{make} in subdirectories, you should run it using the @code{make} variable @code{MAKE}. Most versions of @command{make} set @code{MAKE} to the name of the @command{make} program plus any options it was given. (But many do not include in it the values of any variables set on the command line, so those are not passed on automatically.) Some old versions of @command{make} do not set this variable. The following macro allows you to use it even with those versions. @defmac AC_PROG_MAKE_SET @acindex{PROG_MAKE_SET} @ovindex SET_MAKE If the Make command, @code{$MAKE} if set or else @samp{make}, predefines @code{$(MAKE)}, define output variable @code{SET_MAKE} to be empty. Otherwise, define @code{SET_MAKE} to a macro definition that sets @code{$(MAKE)}, such as @samp{MAKE=make}. Calls @code{AC_SUBST} for @code{SET_MAKE}. @end defmac If you use this macro, place a line like this in each @file{Makefile.in} that runs @code{MAKE} on other directories: @example @@SET_MAKE@@ @end example @node Configuration Actions @section Performing Configuration Actions @cindex Configuration actions @file{configure} is designed so that it appears to do everything itself, but there is actually a hidden slave: @file{config.status}. @file{configure} is in charge of examining your system, but it is @file{config.status} that actually takes the proper actions based on the results of @file{configure}. The most typical task of @file{config.status} is to @emph{instantiate} files. This section describes the common behavior of the four standard instantiating macros: @code{AC_CONFIG_FILES}, @code{AC_CONFIG_HEADERS}, @code{AC_CONFIG_COMMANDS} and @code{AC_CONFIG_LINKS}. They all have this prototype: @c FIXME: Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something @c awful. @example AC_CONFIG_FOOS(@var{tag}@dots{}, [@var{commands}], [@var{init-cmds}]) @end example @noindent where the arguments are: @table @var @item tag@dots{} A blank-or-newline-separated list of tags, which are typically the names of the files to instantiate. You are encouraged to use literals as @var{tags}. In particular, you should avoid @example @dots{} && my_foos="$my_foos fooo" @dots{} && my_foos="$my_foos foooo" AC_CONFIG_FOOS([$my_foos]) @end example @noindent and use this instead: @example @dots{} && AC_CONFIG_FOOS([fooo]) @dots{} && AC_CONFIG_FOOS([foooo]) @end example The macros @code{AC_CONFIG_FILES} and @code{AC_CONFIG_HEADERS} use special @var{tag} values: they may have the form @samp{@var{output}} or @samp{@var{output}:@var{inputs}}. The file @var{output} is instantiated from its templates, @var{inputs} (defaulting to @samp{@var{output}.in}). @samp{AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk)]}, for example, asks for the creation of the file @file{Makefile} that contains the expansion of the output variables in the concatenation of @file{boiler/top.mk} and @file{boiler/bot.mk}. The special value @samp{-} might be used to denote the standard output when used in @var{output}, or the standard input when used in the @var{inputs}. You most probably don't need to use this in @file{configure.ac}, but it is convenient when using the command line interface of @file{./config.status}, see @ref{config.status Invocation}, for more details. The @var{inputs} may be absolute or relative file names. In the latter case they are first looked for in the build tree, and then in the source tree. @item commands Shell commands output literally into @file{config.status}, and associated with a tag that the user can use to tell @file{config.status} which the commands to run. The commands are run each time a @var{tag} request is given to @file{config.status}, typically each time the file @file{@var{tag}} is created. The variables set during the execution of @command{configure} are @emph{not} available here: you first need to set them via the @var{init-cmds}. Nonetheless the following variables are precomputed: @table @code @item srcdir The name of the top source directory, assuming that the working directory is the top build directory. This is what the @command{configure} option @option{--srcdir} sets. @item ac_top_srcdir The name of the top source directory, assuming that the working directory is the current build directory. @item ac_top_build_prefix The name of the top build directory, assuming that the working directory is the current build directory. It can be empty, or else ends with a slash, so that you may concatenate it. @item ac_srcdir The name of the corresponding source directory, assuming that the working directory is the current build directory. @end table @noindent The @dfn{current} directory refers to the directory (or pseudo-directory) containing the input part of @var{tags}. For instance, running @example AC_CONFIG_COMMANDS([deep/dir/out:in/in.in], [@dots{}], [@dots{}]) @end example @noindent with @option{--srcdir=../package} produces the following values: @example # Argument of --srcdir srcdir='../package' # Reversing deep/dir ac_top_build_prefix='../../' # Concatenation of $ac_top_build_prefix and srcdir ac_top_srcdir='../../../package' # Concatenation of $ac_top_srcdir and deep/dir ac_srcdir='../../../package/deep/dir' @end example @noindent independently of @samp{in/in.in}. @item init-cmds Shell commands output @emph{unquoted} near the beginning of @file{config.status}, and executed each time @file{config.status} runs (regardless of the tag). Because they are unquoted, for example, @samp{$var} is output as the value of @code{var}. @var{init-cmds} is typically used by @file{configure} to give @file{config.status} some variables it needs to run the @var{commands}. You should be extremely cautious in your variable names: all the @var{init-cmds} share the same name space and may overwrite each other in unpredictable ways. Sorry@enddots{} @end table All these macros can be called multiple times, with different @var{tag} values, of course! @node Configuration Files @section Creating Configuration Files @cindex Creating configuration files @cindex Configuration file creation Be sure to read the previous section, @ref{Configuration Actions}. @defmac AC_CONFIG_FILES (@var{file}@dots{}, @ovar{cmds}, @ovar{init-cmds}) @acindex{CONFIG_FILES} Make @code{AC_OUTPUT} create each @file{@var{file}} by copying an input file (by default @file{@var{file}.in}), substituting the output variable values. @c Before we used to have this feature, which was later rejected @c because it complicates the writing of makefiles: @c If the file would be unchanged, it is left untouched, to preserve @c timestamp. This macro is one of the instantiating macros; see @ref{Configuration Actions}. @xref{Makefile Substitutions}, for more information on using output variables. @xref{Setting Output Variables}, for more information on creating them. This macro creates the directory that the file is in if it doesn't exist. Usually, makefiles are created this way, but other files, such as @file{.gdbinit}, can be specified as well. Typical calls to @code{AC_CONFIG_FILES} look like this: @example AC_CONFIG_FILES([Makefile src/Makefile man/Makefile X/Imakefile]) AC_CONFIG_FILES([autoconf], [chmod +x autoconf]) @end example You can override an input file name by appending to @var{file} a colon-separated list of input files. Examples: @example AC_CONFIG_FILES([Makefile:boiler/top.mk:boiler/bot.mk] [lib/Makefile:boiler/lib.mk]) @end example @noindent Doing this allows you to keep your file names acceptable to @acronym{DOS} variants, or to prepend and/or append boilerplate to the file. @end defmac @node Makefile Substitutions @section Substitutions in Makefiles @cindex Substitutions in makefiles @cindex Makefile substitutions Each subdirectory in a distribution that contains something to be compiled or installed should come with a file @file{Makefile.in}, from which @command{configure} creates a file @file{Makefile} in that directory. To create @file{Makefile}, @command{configure} performs a simple variable substitution, replacing occurrences of @samp{@@@var{variable}@@} in @file{Makefile.in} with the value that @command{configure} has determined for that variable. Variables that are substituted into output files in this way are called @dfn{output variables}. They are ordinary shell variables that are set in @command{configure}. To make @command{configure} substitute a particular variable into the output files, the macro @code{AC_SUBST} must be called with that variable name as an argument. Any occurrences of @samp{@@@var{variable}@@} for other variables are left unchanged. @xref{Setting Output Variables}, for more information on creating output variables with @code{AC_SUBST}. A software package that uses a @command{configure} script should be distributed with a file @file{Makefile.in}, but no makefile; that way, the user has to properly configure the package for the local system before compiling it. @xref{Makefile Conventions, , Makefile Conventions, standards, The @acronym{GNU} Coding Standards}, for more information on what to put in makefiles. @menu * Preset Output Variables:: Output variables that are always set * Installation Directory Variables:: Other preset output variables * Changed Directory Variables:: Warnings about @file{datarootdir} * Build Directories:: Supporting multiple concurrent compiles * Automatic Remaking:: Makefile rules for configuring @end menu @node Preset Output Variables @subsection Preset Output Variables @cindex Output variables Some output variables are preset by the Autoconf macros. Some of the Autoconf macros set additional output variables, which are mentioned in the descriptions for those macros. @xref{Output Variable Index}, for a complete list of output variables. @xref{Installation Directory Variables}, for the list of the preset ones related to installation directories. Below are listed the other preset ones. They all are precious variables (@pxref{Setting Output Variables}, @code{AC_ARG_VAR}). @c Just say no to ASCII sorting! We're humans, not computers. @c These variables are listed as they would be in a dictionary: @c actor @c Actress @c actress @defvar CFLAGS @ovindex CFLAGS Debugging and optimization options for the C compiler. If it is not set in the environment when @command{configure} runs, the default value is set when you call @code{AC_PROG_CC} (or empty if you don't). @command{configure} uses this variable when compiling or linking programs to test for C features. If a compiler option affects only the behavior of the preprocessor (e.g., @option{-D @var{name}}), it should be put into @code{CPPFLAGS} instead. If it affects only the linker (e.g., @option{-L @var{directory}}), it should be put into @code{LDFLAGS} instead. If it affects only the compiler proper, @code{CFLAGS} is the natural home for it. If an option affects multiple phases of the compiler, though, matters get tricky. One approach to put such options directly into @code{CC}, e.g., @code{CC='gcc -m64'}. Another is to put them into both @code{CPPFLAGS} and @code{LDFLAGS}, but not into @code{CFLAGS}. @end defvar @defvar configure_input @ovindex configure_input A comment saying that the file was generated automatically by @command{configure} and giving the name of the input file. @code{AC_OUTPUT} adds a comment line containing this variable to the top of every makefile it creates. For other files, you should reference this variable in a comment at the top of each input file. For example, an input shell script should begin like this: @example #!/bin/sh # @@configure_input@@ @end example @noindent The presence of that line also reminds people editing the file that it needs to be processed by @command{configure} in order to be used. @end defvar @defvar CPPFLAGS @ovindex CPPFLAGS Preprocessor options for the C, C++, and Objective C preprocessors and compilers. If it is not set in the environment when @command{configure} runs, the default value is empty. @command{configure} uses this variable when preprocessing or compiling programs to test for C, C++, and Objective C features. This variable's contents should contain options like @option{-I}, @option{-D}, and @option{-U} that affect only the behavior of the preprocessor. Please see the explanation of @code{CFLAGS} for what you can do if an option affects other phases of the compiler as well. Currently, @command{configure} always links as part of a single invocation of the compiler that also preprocesses and compiles, so it uses this variable also when linking programs. However, it is unwise to depend on this behavior because the @acronym{GNU} coding standards do not require it and many packages do not use @code{CPPFLAGS} when linking programs. @xref{Special Chars in Variables}, for limitations that @code{CPPFLAGS} might run into. @end defvar @defvar CXXFLAGS @ovindex CXXFLAGS Debugging and optimization options for the C++ compiler. It acts like @code{CFLAGS}, but for C++ instead of C. @end defvar @defvar DEFS @ovindex DEFS @option{-D} options to pass to the C compiler. If @code{AC_CONFIG_HEADERS} is called, @command{configure} replaces @samp{@@DEFS@@} with @option{-DHAVE_CONFIG_H} instead (@pxref{Configuration Headers}). This variable is not defined while @command{configure} is performing its tests, only when creating the output files. @xref{Setting Output Variables}, for how to check the results of previous tests. @end defvar @defvar ECHO_C @defvarx ECHO_N @defvarx ECHO_T @ovindex ECHO_C @ovindex ECHO_N @ovindex ECHO_T How does one suppress the trailing newline from @command{echo} for question-answer message pairs? These variables provide a way: @example echo $ECHO_N "And the winner is... $ECHO_C" sleep 100000000000 echo "$@{ECHO_T@}dead." @end example @noindent Some old and uncommon @command{echo} implementations offer no means to achieve this, in which case @code{ECHO_T} is set to tab. You might not want to use it. @end defvar @defvar ERLCFLAGS @ovindex ERLCFLAGS Debugging and optimization options for the Erlang compiler. If it is not set in the environment when @command{configure} runs, the default value is empty. @command{configure} uses this variable when compiling programs to test for Erlang features. @end defvar @defvar FCFLAGS @ovindex FCFLAGS Debugging and optimization options for the Fortran compiler. If it is not set in the environment when @command{configure} runs, the default value is set when you call @code{AC_PROG_FC} (or empty if you don't). @command{configure} uses this variable when compiling or linking programs to test for Fortran features. @end defvar @defvar FFLAGS @ovindex FFLAGS Debugging and optimization options for the Fortran 77 compiler. If it is not set in the environment when @command{configure} runs, the default value is set when you call @code{AC_PROG_F77} (or empty if you don't). @command{configure} uses this variable when compiling or linking programs to test for Fortran 77 features. @end defvar @defvar LDFLAGS @ovindex LDFLAGS Options for the linker. If it is not set in the environment when @command{configure} runs, the default value is empty. @command{configure} uses this variable when linking programs to test for C, C++, Objective C, and Fortran features. This variable's contents should contain options like @option{-s} and @option{-L} that affect only the behavior of the linker. Please see the explanation of @code{CFLAGS} for what you can do if an option also affects other phases of the compiler. Don't use this variable to pass library names (@option{-l}) to the linker; use @code{LIBS} instead. @end defvar @defvar LIBS @ovindex LIBS @option{-l} options to pass to the linker. The default value is empty, but some Autoconf macros may prepend extra libraries to this variable if those libraries are found and provide necessary functions, see @ref{Libraries}. @command{configure} uses this variable when linking programs to test for C, C++, and Fortran features. @end defvar @defvar OBJCFLAGS @ovindex OBJCFLAGS Debugging and optimization options for the Objective C compiler. It acts like @code{CFLAGS}, but for Objective C instead of C. @end defvar @defvar builddir @ovindex builddir Rigorously equal to @samp{.}. Added for symmetry only. @end defvar @defvar abs_builddir @ovindex abs_builddir Absolute name of @code{builddir}. @end defvar @defvar top_builddir @ovindex top_builddir The relative name of the top level of the current build tree. In the top-level directory, this is the same as @code{builddir}. @end defvar @defvar abs_top_builddir @ovindex abs_top_builddir Absolute name of @code{top_builddir}. @end defvar @defvar srcdir @ovindex srcdir The name of the directory that contains the source code for that makefile. @end defvar @defvar abs_srcdir @ovindex abs_srcdir Absolute name of @code{srcdir}. @end defvar @defvar top_srcdir @ovindex top_srcdir The name of the top-level source code directory for the package. In the top-level directory, this is the same as @code{srcdir}. @end defvar @defvar abs_top_srcdir @ovindex abs_top_srcdir Absolute name of @code{top_srcdir}. @end defvar @node Installation Directory Variables @subsection Installation Directory Variables @cindex Installation directories @cindex Directories, installation The following variables specify the directories for package installation, see @ref{Directory Variables, , Variables for Installation Directories, standards, The @acronym{GNU} Coding Standards}, for more information. See the end of this section for details on when and how to use these variables. @defvar bindir @ovindex bindir The directory for installing executables that users run. @end defvar @defvar datadir @ovindex datadir The directory for installing idiosyncratic read-only architecture-independent data. @end defvar @defvar datarootdir @ovindex datarootdir The root of the directory tree for read-only architecture-independent data files. @end defvar @defvar docdir @ovindex docdir The directory for installing documentation files (other than Info and man). @end defvar @defvar dvidir @ovindex dvidir The directory for installing documentation files in DVI format. @end defvar @defvar exec_prefix @ovindex exec_prefix The installation prefix for architecture-dependent files. By default it's the same as @var{prefix}. You should avoid installing anything directly to @var{exec_prefix}. However, the default value for directories containing architecture-dependent files should be relative to @var{exec_prefix}. @end defvar @defvar htmldir @ovindex htmldir The directory for installing HTML documentation. @end defvar @defvar includedir @ovindex includedir The directory for installing C header files. @end defvar @defvar infodir @ovindex infodir The directory for installing documentation in Info format. @end defvar @defvar libdir @ovindex libdir The directory for installing object code libraries. @end defvar @defvar libexecdir @ovindex libexecdir The directory for installing executables that other programs run. @end defvar @defvar localedir @ovindex localedir The directory for installing locale-dependent but architecture-independent data, such as message catalogs. This directory usually has a subdirectory per locale. @end defvar @defvar localstatedir @ovindex localstatedir The directory for installing modifiable single-machine data. @end defvar @defvar mandir @ovindex mandir The top-level directory for installing documentation in man format. @end defvar @defvar oldincludedir @ovindex oldincludedir The directory for installing C header files for non-@acronym{GCC} compilers. @end defvar @defvar pdfdir @ovindex pdfdir The directory for installing PDF documentation. @end defvar @defvar prefix @ovindex prefix The common installation prefix for all files. If @var{exec_prefix} is defined to a different value, @var{prefix} is used only for architecture-independent files. @end defvar @defvar psdir @ovindex psdir The directory for installing PostScript documentation. @end defvar @defvar sbindir @ovindex sbindir The directory for installing executables that system administrators run. @end defvar @defvar sharedstatedir @ovindex sharedstatedir The directory for installing modifiable architecture-independent data. @end defvar @defvar sysconfdir @ovindex sysconfdir The directory for installing read-only single-machine data. @end defvar Most of these variables have values that rely on @code{prefix} or @code{exec_prefix}. It is deliberate that the directory output variables keep them unexpanded: typically @samp{@@datarootdir@@} is replaced by @samp{$@{prefix@}/share}, not @samp{/usr/local/share}, and @samp{@@datadir@@} is replaced by @samp{$@{datarootdir@}}. This behavior is mandated by the @acronym{GNU} coding standards, so that when the user runs: @table @samp @item make she can still specify a different prefix from the one specified to @command{configure}, in which case, if needed, the package should hard code dependencies corresponding to the make-specified prefix. @item make install she can specify a different installation location, in which case the package @emph{must} still depend on the location which was compiled in (i.e., never recompile when @samp{make install} is run). This is an extremely important feature, as many people may decide to install all the files of a package grouped together, and then install links from the final locations to there. @end table In order to support these features, it is essential that @code{datarootdir} remains being defined as @samp{$@{prefix@}/share} to depend upon the current value of @code{prefix}. A corollary is that you should not use these variables except in makefiles. For instance, instead of trying to evaluate @code{datadir} in @file{configure} and hard-coding it in makefiles using e.g., @samp{AC_DEFINE_UNQUOTED([DATADIR], ["$datadir"], [Data directory.])}, you should add @option{-DDATADIR='$(datadir)'} to your makefile's definition of @code{CPPFLAGS} (@code{AM_CPPFLAGS} if you are also using Automake). Similarly, you should not rely on @code{AC_CONFIG_FILES} to replace @code{datadir} and friends in your shell scripts and other files; instead, let @command{make} manage their replacement. For instance Autoconf ships templates of its shell scripts ending with @samp{.in}, and uses a makefile snippet similar to the following to build scripts like @command{autoheader} and @command{autom4te}: @example @group edit = sed \ -e 's|@@datadir[@@]|$(pkgdatadir)|g' \ -e 's|@@prefix[@@]|$(prefix)|g' @end group @group autoheader autom4te: Makefile rm -f $@@ $@@.tmp $(edit) '$(srcdir)/$@@.in' >$@@.tmp chmod +x $@@.tmp chmod a-w $@@.tmp mv $@@.tmp $@@ @end group @group autoheader: $(srcdir)/autoheader.in autom4te: $(srcdir)/autom4te.in @end group @end example Some details are noteworthy: @table @asis @item @samp{@@datadir[@@]} The brackets prevent @command{configure} from replacing @samp{@@datadir@@} in the Sed expression itself. Brackets are preferable to a backslash here, since Posix says @samp{\@@} is not portable. @item @samp{$(pkgdatadir)} Don't use @samp{@@pkgdatadir@@}! Use the matching makefile variable instead. @item @samp{/} Don't use @samp{/} in the Sed expressions that replace file names since most likely the variables you use, such as @samp{$(pkgdatadir)}, contain @samp{/}. Use a shell metacharacter instead, such as @samp{|}. @item special characters File names, file name components, and the value of @code{VPATH} should not contain shell metacharacters or white space. @xref{Special Chars in Variables}. @item dependency on @file{Makefile} Since @code{edit} uses values that depend on the configuration specific values (@code{prefix}, etc.)@: and not only on @code{VERSION} and so forth, the output depends on @file{Makefile}, not @file{configure.ac}. @item @samp{$@@} The main rule is generic, and uses @samp{$@@} extensively to avoid the need for multiple copies of the rule. @item Separated dependencies and single suffix rules You can't use them! The above snippet cannot be (portably) rewritten as: @example autoconf autoheader: Makefile @group .in: rm -f $@@ $@@.tmp $(edit) $< >$@@.tmp chmod +x $@@.tmp mv $@@.tmp $@@ @end group @end example @xref{Single Suffix Rules}, for details. @item @samp{$(srcdir)} Be sure to specify the name of the source directory, otherwise the package won't support separated builds. @end table For the more specific installation of Erlang libraries, the following variables are defined: @defvar ERLANG_INSTALL_LIB_DIR @ovindex ERLANG_INSTALL_LIB_DIR @acindex{ERLANG_SUBST_INSTALL_LIB_DIR} The common parent directory of Erlang library installation directories. This variable is set by calling the @code{AC_ERLANG_SUBST_INSTALL_LIB_DIR} macro in @file{configure.ac}. @end defvar @defvar ERLANG_INSTALL_LIB_DIR_@var{library} @ovindex ERLANG_INSTALL_LIB_DIR_@var{library} @acindex{ERLANG_SUBST_INSTALL_LIB_SUBDIR} The installation directory for Erlang library @var{library}. This variable is set by calling the @samp{AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR(@var{library}, @var{version}} macro in @file{configure.ac}. @end defvar @xref{Erlang Libraries}, for details. @node Changed Directory Variables @subsection Changed Directory Variables @cindex @file{datarootdir} In Autoconf 2.60, the set of directory variables has changed, and the defaults of some variables have been adjusted (@pxref{Installation Directory Variables}) to changes in the @acronym{GNU} Coding Standards. Notably, @file{datadir}, @file{infodir}, and @file{mandir} are now expressed in terms of @file{datarootdir}. If you are upgrading from an earlier Autoconf version, you may need to adjust your files to ensure that the directory variables are substituted correctly (@pxref{Defining Directories}), and that a definition of @file{datarootdir} is in place. For example, in a @file{Makefile.in}, adding @example datarootdir = @@datarootdir@@ @end example @noindent is usually sufficient. If you use Automake to create @file{Makefile.in}, it will add this for you. To help with the transition, Autoconf warns about files that seem to use @code{datarootdir} without defining it. In some cases, it then expands the value of @code{$datarootdir} in substitutions of the directory variables. The following example shows such a warning: @example $ @kbd{cat configure.ac} AC_INIT AC_CONFIG_FILES([Makefile]) AC_OUTPUT $ @kbd{cat Makefile.in} prefix = @@prefix@@ datadir = @@datadir@@ $ @kbd{autoconf} $ @kbd{configure} configure: creating ./config.status config.status: creating Makefile config.status: WARNING: Makefile.in seems to ignore the --datarootdir setting $ @kbd{cat Makefile} prefix = /usr/local datadir = $@{prefix@}/share @end example Usually one can easily change the file to accommodate both older and newer Autoconf releases: @example $ @kbd{cat Makefile.in} prefix = @@prefix@@ datarootdir = @@datarootdir@@ datadir = @@datadir@@ $ @kbd{configure} configure: creating ./config.status config.status: creating Makefile $ @kbd{cat Makefile} prefix = /usr/local datarootdir = $@{prefix@}/share datadir = $@{datarootdir@} @end example @acindex{DATAROOTDIR_CHECKED} In some cases, however, the checks may not be able to detect that a suitable initialization of @code{datarootdir} is in place, or they may fail to detect that such an initialization is necessary in the output file. If, after auditing your package, there are still spurious @file{configure} warnings about @code{datarootdir}, you may add the line @example AC_DEFUN([AC_DATAROOTDIR_CHECKED]) @end example @noindent to your @file{configure.ac} to disable the warnings. This is an exception to the usual rule that you should not define a macro whose name begins with @code{AC_} (@pxref{Macro Names}). @node Build Directories @subsection Build Directories @cindex Build directories @cindex Directories, build You can support compiling a software package for several architectures simultaneously from the same copy of the source code. The object files for each architecture are kept in their own directory. To support doing this, @command{make} uses the @code{VPATH} variable to find the files that are in the source directory. @acronym{GNU} Make and most other recent @command{make} programs can do this. Older @command{make} programs do not support @code{VPATH}; when using them, the source code must be in the same directory as the object files. To support @code{VPATH}, each @file{Makefile.in} should contain two lines that look like: @example srcdir = @@srcdir@@ VPATH = @@srcdir@@ @end example Do not set @code{VPATH} to the value of another variable, for example @samp{VPATH = $(srcdir)}, because some versions of @command{make} do not do variable substitutions on the value of @code{VPATH}. @command{configure} substitutes the correct value for @code{srcdir} when it produces @file{Makefile}. Do not use the @code{make} variable @code{$<}, which expands to the file name of the file in the source directory (found with @code{VPATH}), except in implicit rules. (An implicit rule is one such as @samp{.c.o}, which tells how to create a @file{.o} file from a @file{.c} file.) Some versions of @command{make} do not set @code{$<} in explicit rules; they expand it to an empty value. Instead, Make command lines should always refer to source files by prefixing them with @samp{$(srcdir)/}. For example: @example time.info: time.texinfo $(MAKEINFO) '$(srcdir)/time.texinfo' @end example @node Automatic Remaking @subsection Automatic Remaking @cindex Automatic remaking @cindex Remaking automatically You can put rules like the following in the top-level @file{Makefile.in} for a package to automatically update the configuration information when you change the configuration files. This example includes all of the optional files, such as @file{aclocal.m4} and those related to configuration header files. Omit from the @file{Makefile.in} rules for any of these files that your package does not use. The @samp{$(srcdir)/} prefix is included because of limitations in the @code{VPATH} mechanism. The @file{stamp-} files are necessary because the timestamps of @file{config.h.in} and @file{config.h} are not changed if remaking them does not change their contents. This feature avoids unnecessary recompilation. You should include the file @file{stamp-h.in} your package's distribution, so that @command{make} considers @file{config.h.in} up to date. Don't use @command{touch} (@pxref{Limitations of Usual Tools}); instead, use @command{echo} (using @command{date} would cause needless differences, hence @acronym{CVS} conflicts, etc.). @example @group $(srcdir)/configure: configure.ac aclocal.m4 cd '$(srcdir)' && autoconf # autoheader might not change config.h.in, so touch a stamp file. $(srcdir)/config.h.in: stamp-h.in $(srcdir)/stamp-h.in: configure.ac aclocal.m4 cd '$(srcdir)' && autoheader echo timestamp > '$(srcdir)/stamp-h.in' config.h: stamp-h stamp-h: config.h.in config.status ./config.status Makefile: Makefile.in config.status ./config.status config.status: configure ./config.status --recheck @end group @end example @noindent (Be careful if you copy these lines directly into your makefile, as you need to convert the indented lines to start with the tab character.) In addition, you should use @example AC_CONFIG_FILES([stamp-h], [echo timestamp > stamp-h]) @end example @noindent so @file{config.status} ensures that @file{config.h} is considered up to date. @xref{Output}, for more information about @code{AC_OUTPUT}. @xref{config.status Invocation}, for more examples of handling configuration-related dependencies. @node Configuration Headers @section Configuration Header Files @cindex Configuration Header @cindex @file{config.h} When a package contains more than a few tests that define C preprocessor symbols, the command lines to pass @option{-D} options to the compiler can get quite long. This causes two problems. One is that the @command{make} output is hard to visually scan for errors. More seriously, the command lines can exceed the length limits of some operating systems. As an alternative to passing @option{-D} options to the compiler, @command{configure} scripts can create a C header file containing @samp{#define} directives. The @code{AC_CONFIG_HEADERS} macro selects this kind of output. Though it can be called anywhere between @code{AC_INIT} and @code{AC_OUTPUT}, it is customary to call it right after @code{AC_INIT}. The package should @samp{#include} the configuration header file before any other header files, to prevent inconsistencies in declarations (for example, if it redefines @code{const}). To provide for VPATH builds, remember to pass the C compiler a @option{-I.} option (or @option{-I..}; whichever directory contains @file{config.h}). Even if you use @samp{#include "config.h"}, the preprocessor searches only the directory of the currently read file, i.e., the source directory, not the build directory. With the appropriate @option{-I} option, you can use @samp{#include }. Actually, it's a good habit to use it, because in the rare case when the source directory contains another @file{config.h}, the build directory should be searched first. @defmac AC_CONFIG_HEADERS (@var{header} @dots{}, @ovar{cmds}, @ovar{init-cmds}) @acindex{CONFIG_HEADERS} @cvindex HAVE_CONFIG_H This macro is one of the instantiating macros; see @ref{Configuration Actions}. Make @code{AC_OUTPUT} create the file(s) in the blank-or-newline-separated list @var{header} containing C preprocessor @code{#define} statements, and replace @samp{@@DEFS@@} in generated files with @option{-DHAVE_CONFIG_H} instead of the value of @code{DEFS}. The usual name for @var{header} is @file{config.h}. If @var{header} already exists and its contents are identical to what @code{AC_OUTPUT} would put in it, it is left alone. Doing this allows making some changes in the configuration without needlessly causing object files that depend on the header file to be recompiled. Usually the input file is named @file{@var{header}.in}; however, you can override the input file name by appending to @var{header} a colon-separated list of input files. Examples: @example AC_CONFIG_HEADERS([config.h:config.hin]) AC_CONFIG_HEADERS([defines.h:defs.pre:defines.h.in:defs.post]) @end example @noindent Doing this allows you to keep your file names acceptable to @acronym{DOS} variants, or to prepend and/or append boilerplate to the file. @end defmac @defmac AH_HEADER @ahindex{HEADER} This macro is defined as the name of the first declared config header and undefined if no config headers have been declared up to this point. A third-party macro may, for example, require use of a config header without invoking AC_CONFIG_HEADERS twice, like this: @example AC_CONFIG_COMMANDS_PRE( [m4_ifndef([AH_HEADER], [AC_CONFIG_HEADERS([config.h])])]) @end example @end defmac @xref{Configuration Actions}, for more details on @var{header}. @menu * Header Templates:: Input for the configuration headers * autoheader Invocation:: How to create configuration templates * Autoheader Macros:: How to specify CPP templates @end menu @node Header Templates @subsection Configuration Header Templates @cindex Configuration Header Template @cindex Header templates @cindex @file{config.h.in} Your distribution should contain a template file that looks as you want the final header file to look, including comments, with @code{#undef} statements which are used as hooks. For example, suppose your @file{configure.ac} makes these calls: @example AC_CONFIG_HEADERS([conf.h]) AC_CHECK_HEADERS([unistd.h]) @end example @noindent Then you could have code like the following in @file{conf.h.in}. On systems that have @file{unistd.h}, @command{configure} defines @samp{HAVE_UNISTD_H} to 1. On other systems, the whole line is commented out (in case the system predefines that symbol). @example @group /* Define as 1 if you have unistd.h. */ #undef HAVE_UNISTD_H @end group @end example Pay attention that @samp{#undef} is in the first column, and there is nothing after @samp{HAVE_UNISTD_H}, not even white space. You can then decode the configuration header using the preprocessor directives: @example @group #include #ifdef HAVE_UNISTD_H # include #else /* We are in trouble. */ #endif @end group @end example The use of old form templates, with @samp{#define} instead of @samp{#undef} is strongly discouraged. Similarly with old templates with comments on the same line as the @samp{#undef}. Anyway, putting comments in preprocessor macros has never been a good idea. Since it is a tedious task to keep a template header up to date, you may use @command{autoheader} to generate it, see @ref{autoheader Invocation}. @node autoheader Invocation @subsection Using @command{autoheader} to Create @file{config.h.in} @cindex @command{autoheader} The @command{autoheader} program can create a template file of C @samp{#define} statements for @command{configure} to use. If @file{configure.ac} invokes @code{AC_CONFIG_HEADERS(@var{file})}, @command{autoheader} creates @file{@var{file}.in}; if multiple file arguments are given, the first one is used. Otherwise, @command{autoheader} creates @file{config.h.in}. In order to do its job, @command{autoheader} needs you to document all of the symbols that you might use. Typically this is done via an @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED} call whose first argument is a literal symbol and whose third argument describes the symbol (@pxref{Defining Symbols}). Alternatively, you can use @code{AH_TEMPLATE} (@pxref{Autoheader Macros}), or you can supply a suitable input file for a subsequent configuration header file. Symbols defined by Autoconf's builtin tests are already documented properly; you need to document only those that you define yourself. You might wonder why @command{autoheader} is needed: after all, why would @command{configure} need to ``patch'' a @file{config.h.in} to produce a @file{config.h} instead of just creating @file{config.h} from scratch? Well, when everything rocks, the answer is just that we are wasting our time maintaining @command{autoheader}: generating @file{config.h} directly is all that is needed. When things go wrong, however, you'll be thankful for the existence of @command{autoheader}. The fact that the symbols are documented is important in order to @emph{check} that @file{config.h} makes sense. The fact that there is a well-defined list of symbols that should be defined (or not) is also important for people who are porting packages to environments where @command{configure} cannot be run: they just have to @emph{fill in the blanks}. But let's come back to the point: the invocation of @command{autoheader}@dots{} If you give @command{autoheader} an argument, it uses that file instead of @file{configure.ac} and writes the header file to the standard output instead of to @file{config.h.in}. If you give @command{autoheader} an argument of @option{-}, it reads the standard input instead of @file{configure.ac} and writes the header file to the standard output. @command{autoheader} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Report processing steps. @item --debug @itemx -d Don't remove the temporary files. @item --force @itemx -f Remake the template file even if newer than its input files. @item --include=@var{dir} @itemx -I @var{dir} Append @var{dir} to the include path. Multiple invocations accumulate. @item --prepend-include=@var{dir} @item -B @var{dir} Prepend @var{dir} to the include path. Multiple invocations accumulate. @item --warnings=@var{category} @itemx -W @var{category} @evindex WARNINGS Report the warnings related to @var{category} (which can actually be a comma separated list). Current categories include: @table @samp @item obsolete report the uses of obsolete constructs @item all report all the warnings @item none report none @item error treats warnings as errors @item no-@var{category} disable warnings falling into @var{category} @end table @end table @node Autoheader Macros @subsection Autoheader Macros @cindex Autoheader macros @command{autoheader} scans @file{configure.ac} and figures out which C preprocessor symbols it might define. It knows how to generate templates for symbols defined by @code{AC_CHECK_HEADERS}, @code{AC_CHECK_FUNCS} etc., but if you @code{AC_DEFINE} any additional symbol, you must define a template for it. If there are missing templates, @command{autoheader} fails with an error message. The template for a @var{symbol} is created by @command{autoheader} from the @var{description} argument to an @code{AC_DEFINE}; see @ref{Defining Symbols}. For special needs, you can use the following macros. @defmac AH_TEMPLATE (@var{key}, @var{description}) @ahindex{TEMPLATE} Tell @command{autoheader} to generate a template for @var{key}. This macro generates standard templates just like @code{AC_DEFINE} when a @var{description} is given. For example: @example AH_TEMPLATE([CRAY_STACKSEG_END], [Define to one of _getb67, GETB67, getb67 for Cray-2 and Cray-YMP systems. This function is required for alloca.c support on those systems.]) @end example @noindent generates the following template, with the description properly justified. @example /* Define to one of _getb67, GETB67, getb67 for Cray-2 and Cray-YMP systems. This function is required for alloca.c support on those systems. */ #undef CRAY_STACKSEG_END @end example @end defmac @defmac AH_VERBATIM (@var{key}, @var{template}) @ahindex{VERBATIM} Tell @command{autoheader} to include the @var{template} as-is in the header template file. This @var{template} is associated with the @var{key}, which is used to sort all the different templates and guarantee their uniqueness. It should be a symbol that can be defined via @code{AC_DEFINE}. @end defmac @defmac AH_TOP (@var{text}) @ahindex{TOP} Include @var{text} at the top of the header template file. @end defmac @defmac AH_BOTTOM (@var{text}) @ahindex{BOTTOM} Include @var{text} at the bottom of the header template file. @end defmac Please note that @var{text} gets included ``verbatim'' to the template file, not to the resulting config header, so it can easily get mangled when the template is processed. There is rarely a need for something other than @example AH_BOTTOM([#include ]) @end example @node Configuration Commands @section Running Arbitrary Configuration Commands @cindex Configuration commands @cindex Commands for configuration You can execute arbitrary commands before, during, and after @file{config.status} is run. The three following macros accumulate the commands to run when they are called multiple times. @code{AC_CONFIG_COMMANDS} replaces the obsolete macro @code{AC_OUTPUT_COMMANDS}; see @ref{Obsolete Macros}, for details. @defmac AC_CONFIG_COMMANDS (@var{tag}@dots{}, @ovar{cmds}, @ovar{init-cmds}) @acindex{CONFIG_COMMANDS} Specify additional shell commands to run at the end of @file{config.status}, and shell commands to initialize any variables from @command{configure}. Associate the commands with @var{tag}. Since typically the @var{cmds} create a file, @var{tag} should naturally be the name of that file. If needed, the directory hosting @var{tag} is created. This macro is one of the instantiating macros; see @ref{Configuration Actions}. Here is an unrealistic example: @example fubar=42 AC_CONFIG_COMMANDS([fubar], [echo this is extra $fubar, and so on.], [fubar=$fubar]) @end example Here is a better one: @example AC_CONFIG_COMMANDS([timestamp], [date >timestamp]) @end example @end defmac The following two macros look similar, but in fact they are not of the same breed: they are executed directly by @file{configure}, so you cannot use @file{config.status} to rerun them. @c Yet it is good to leave them here. The user sees them together and @c decides which best fits their needs. @defmac AC_CONFIG_COMMANDS_PRE (@var{cmds}) @acindex{CONFIG_COMMANDS_PRE} Execute the @var{cmds} right before creating @file{config.status}. This macro presents the last opportunity to call @code{AC_SUBST}, @code{AC_DEFINE}, or @code{AC_CONFIG_FOOS} macros. @end defmac @defmac AC_CONFIG_COMMANDS_POST (@var{cmds}) @acindex{CONFIG_COMMANDS_POST} Execute the @var{cmds} right after creating @file{config.status}. @end defmac @node Configuration Links @section Creating Configuration Links @cindex Configuration links @cindex Links for configuration You may find it convenient to create links whose destinations depend upon results of tests. One can use @code{AC_CONFIG_COMMANDS} but the creation of relative symbolic links can be delicate when the package is built in a directory different from the source directory. @defmac AC_CONFIG_LINKS (@var{dest}:@var{source}@dots{}, @ovar{cmds}, @ovar{init-cmds}) @acindex{CONFIG_LINKS} @cindex Links Make @code{AC_OUTPUT} link each of the existing files @var{source} to the corresponding link name @var{dest}. Makes a symbolic link if possible, otherwise a hard link if possible, otherwise a copy. The @var{dest} and @var{source} names should be relative to the top level source or build directory. This macro is one of the instantiating macros; see @ref{Configuration Actions}. For example, this call: @example AC_CONFIG_LINKS([host.h:config/$machine.h object.h:config/$obj_format.h]) @end example @noindent creates in the current directory @file{host.h} as a link to @file{@var{srcdir}/config/$machine.h}, and @file{object.h} as a link to @file{@var{srcdir}/config/$obj_format.h}. The tempting value @samp{.} for @var{dest} is invalid: it makes it impossible for @samp{config.status} to guess the links to establish. One can then run: @example ./config.status host.h object.h @end example @noindent to create the links. @end defmac @node Subdirectories @section Configuring Other Packages in Subdirectories @cindex Configure subdirectories @cindex Subdirectory configure In most situations, calling @code{AC_OUTPUT} is sufficient to produce makefiles in subdirectories. However, @command{configure} scripts that control more than one independent package can use @code{AC_CONFIG_SUBDIRS} to run @command{configure} scripts for other packages in subdirectories. @defmac AC_CONFIG_SUBDIRS (@var{dir} @dots{}) @acindex{CONFIG_SUBDIRS} @ovindex subdirs Make @code{AC_OUTPUT} run @command{configure} in each subdirectory @var{dir} in the given blank-or-newline-separated list. Each @var{dir} should be a literal, i.e., please do not use: @example if test "$package_foo_enabled" = yes; then $my_subdirs="$my_subdirs foo" fi AC_CONFIG_SUBDIRS([$my_subdirs]) @end example @noindent because this prevents @samp{./configure --help=recursive} from displaying the options of the package @code{foo}. Instead, you should write: @example if test "$package_foo_enabled" = yes; then AC_CONFIG_SUBDIRS([foo]) fi @end example If a given @var{dir} is not found, an error is reported: if the subdirectory is optional, write: @example if test -d "$srcdir/foo"; then AC_CONFIG_SUBDIRS([foo]) fi @end example @c NB: Yes, below we mean configure.in, not configure.ac. If a given @var{dir} contains @command{configure.gnu}, it is run instead of @command{configure}. This is for packages that might use a non-Autoconf script @command{Configure}, which can't be called through a wrapper @command{configure} since it would be the same file on case-insensitive file systems. Likewise, if a @var{dir} contains @file{configure.in} but no @command{configure}, the Cygnus @command{configure} script found by @code{AC_CONFIG_AUX_DIR} is used. The subdirectory @command{configure} scripts are given the same command line options that were given to this @command{configure} script, with minor changes if needed, which include: @itemize @minus @item adjusting a relative name for the cache file; @item adjusting a relative name for the source directory; @item propagating the current value of @code{$prefix}, including if it was defaulted, and if the default values of the top level and of the subdirectory @file{configure} differ. @end itemize This macro also sets the output variable @code{subdirs} to the list of directories @samp{@var{dir} @dots{}}. Make rules can use this variable to determine which subdirectories to recurse into. This macro may be called multiple times. @end defmac @node Default Prefix @section Default Prefix @cindex Install prefix @cindex Prefix for install By default, @command{configure} sets the prefix for files it installs to @file{/usr/local}. The user of @command{configure} can select a different prefix using the @option{--prefix} and @option{--exec-prefix} options. There are two ways to change the default: when creating @command{configure}, and when running it. Some software packages might want to install in a directory other than @file{/usr/local} by default. To accomplish that, use the @code{AC_PREFIX_DEFAULT} macro. @defmac AC_PREFIX_DEFAULT (@var{prefix}) @acindex{PREFIX_DEFAULT} Set the default installation prefix to @var{prefix} instead of @file{/usr/local}. @end defmac It may be convenient for users to have @command{configure} guess the installation prefix from the location of a related program that they have already installed. If you wish to do that, you can call @code{AC_PREFIX_PROGRAM}. @defmac AC_PREFIX_PROGRAM (@var{program}) @acindex{PREFIX_PROGRAM} If the user did not specify an installation prefix (using the @option{--prefix} option), guess a value for it by looking for @var{program} in @env{PATH}, the way the shell does. If @var{program} is found, set the prefix to the parent of the directory containing @var{program}, else default the prefix as described above (@file{/usr/local} or @code{AC_PREFIX_DEFAULT}). For example, if @var{program} is @code{gcc} and the @env{PATH} contains @file{/usr/local/gnu/bin/gcc}, set the prefix to @file{/usr/local/gnu}. @end defmac @c ======================================================== Existing tests @node Existing Tests @chapter Existing Tests These macros test for particular system features that packages might need or want to use. If you need to test for a kind of feature that none of these macros check for, you can probably do it by calling primitive test macros with appropriate arguments (@pxref{Writing Tests}). These tests print messages telling the user which feature they're checking for, and what they find. They cache their results for future @command{configure} runs (@pxref{Caching Results}). Some of these macros set output variables. @xref{Makefile Substitutions}, for how to get their values. The phrase ``define @var{name}'' is used below as a shorthand to mean ``define the C preprocessor symbol @var{name} to the value 1''. @xref{Defining Symbols}, for how to get those symbol definitions into your program. @menu * Common Behavior:: Macros' standard schemes * Alternative Programs:: Selecting between alternative programs * Files:: Checking for the existence of files * Libraries:: Library archives that might be missing * Library Functions:: C library functions that might be missing * Header Files:: Header files that might be missing * Declarations:: Declarations that may be missing * Structures:: Structures or members that might be missing * Types:: Types that might be missing * Compilers and Preprocessors:: Checking for compiling programs * System Services:: Operating system services * Posix Variants:: Special kludges for specific Posix variants * Erlang Libraries:: Checking for the existence of Erlang libraries @end menu @node Common Behavior @section Common Behavior @cindex Common autoconf behavior Much effort has been expended to make Autoconf easy to learn. The most obvious way to reach this goal is simply to enforce standard interfaces and behaviors, avoiding exceptions as much as possible. Because of history and inertia, unfortunately, there are still too many exceptions in Autoconf; nevertheless, this section describes some of the common rules. @menu * Standard Symbols:: Symbols defined by the macros * Default Includes:: Includes used by the generic macros @end menu @node Standard Symbols @subsection Standard Symbols @cindex Standard symbols All the generic macros that @code{AC_DEFINE} a symbol as a result of their test transform their @var{argument} values to a standard alphabet. First, @var{argument} is converted to upper case and any asterisks (@samp{*}) are each converted to @samp{P}. Any remaining characters that are not alphanumeric are converted to underscores. For instance, @example AC_CHECK_TYPES([struct $Expensive*]) @end example @noindent defines the symbol @samp{HAVE_STRUCT__EXPENSIVEP} if the check succeeds. @node Default Includes @subsection Default Includes @cindex Default includes @cindex Includes, default Several tests depend upon a set of header files. Since these headers are not universally available, tests actually have to provide a set of protected includes, such as: @example @group #ifdef TIME_WITH_SYS_TIME # include # include #else # ifdef HAVE_SYS_TIME_H # include # else # include # endif #endif @end group @end example @noindent Unless you know exactly what you are doing, you should avoid using unconditional includes, and check the existence of the headers you include beforehand (@pxref{Header Files}). Most generic macros use the following macro to provide the default set of includes: @defmac AC_INCLUDES_DEFAULT (@ovar{include-directives}) @acindex{INCLUDES_DEFAULT} Expand to @var{include-directives} if defined, otherwise to: @example @group #include #ifdef HAVE_SYS_TYPES_H # include #endif #ifdef HAVE_SYS_STAT_H # include #endif #ifdef STDC_HEADERS # include # include #else # ifdef HAVE_STDLIB_H # include # endif #endif #ifdef HAVE_STRING_H # if !defined STDC_HEADERS && defined HAVE_MEMORY_H # include # endif # include #endif #ifdef HAVE_STRINGS_H # include #endif #ifdef HAVE_INTTYPES_H # include #endif #ifdef HAVE_STDINT_H # include #endif #ifdef HAVE_UNISTD_H # include #endif @end group @end example If the default includes are used, then check for the presence of these headers and their compatibility, i.e., you don't need to run @code{AC_HEADER_STDC}, nor check for @file{stdlib.h} etc. These headers are checked for in the same order as they are included. For instance, on some systems @file{string.h} and @file{strings.h} both exist, but conflict. Then @code{HAVE_STRING_H} is defined, not @code{HAVE_STRINGS_H}. @end defmac @node Alternative Programs @section Alternative Programs @cindex Programs, checking These macros check for the presence or behavior of particular programs. They are used to choose between several alternative programs and to decide what to do once one has been chosen. If there is no macro specifically defined to check for a program you need, and you don't need to check for any special properties of it, then you can use one of the general program-check macros. @menu * Particular Programs:: Special handling to find certain programs * Generic Programs:: How to find other programs @end menu @node Particular Programs @subsection Particular Program Checks These macros check for particular programs---whether they exist, and in some cases whether they support certain features. @defmac AC_PROG_AWK @acindex{PROG_AWK} @ovindex AWK Check for @code{gawk}, @code{mawk}, @code{nawk}, and @code{awk}, in that order, and set output variable @code{AWK} to the first one that is found. It tries @code{gawk} first because that is reported to be the best implementation. @end defmac @defmac AC_PROG_GREP @acindex{PROG_GREP} @ovindex GREP Look for the best available @code{grep} or @code{ggrep} that accepts the longest input lines possible, and that supports multiple @option{-e} options. Set the output variable @code{GREP} to whatever is chosen. @xref{Limitations of Usual Tools}, for more information about portability problems with the @command{grep} command family. @end defmac @defmac AC_PROG_EGREP @acindex{PROG_EGREP} @ovindex EGREP Check whether @code{$GREP -E} works, or else look for the best available @code{egrep} or @code{gegrep} that accepts the longest input lines possible. Set the output variable @code{EGREP} to whatever is chosen. @end defmac @defmac AC_PROG_FGREP @acindex{PROG_FGREP} @ovindex FGREP Check whether @code{$GREP -F} works, or else look for the best available @code{fgrep} or @code{gfgrep} that accepts the longest input lines possible. Set the output variable @code{FGREP} to whatever is chosen. @end defmac @defmac AC_PROG_INSTALL @acindex{PROG_INSTALL} @ovindex INSTALL @ovindex INSTALL_PROGRAM @ovindex INSTALL_DATA @ovindex INSTALL_SCRIPT Set output variable @code{INSTALL} to the name of a @acronym{BSD}-compatible @command{install} program, if one is found in the current @env{PATH}. Otherwise, set @code{INSTALL} to @samp{@var{dir}/install-sh -c}, checking the directories specified to @code{AC_CONFIG_AUX_DIR} (or its default directories) to determine @var{dir} (@pxref{Output}). Also set the variables @code{INSTALL_PROGRAM} and @code{INSTALL_SCRIPT} to @samp{$@{INSTALL@}} and @code{INSTALL_DATA} to @samp{$@{INSTALL@} -m 644}. @samp{@@INSTALL@@} is special, as its value may vary for different configuration files. This macro screens out various instances of @command{install} known not to work. It prefers to find a C program rather than a shell script, for speed. Instead of @file{install-sh}, it can also use @file{install.sh}, but that name is obsolete because some @command{make} programs have a rule that creates @file{install} from it if there is no makefile. Autoconf comes with a copy of @file{install-sh} that you can use. If you use @code{AC_PROG_INSTALL}, you must include either @file{install-sh} or @file{install.sh} in your distribution; otherwise @command{configure} produces an error message saying it can't find them---even if the system you're on has a good @command{install} program. This check is a safety measure to prevent you from accidentally leaving that file out, which would prevent your package from installing on systems that don't have a @acronym{BSD}-compatible @command{install} program. If you need to use your own installation program because it has features not found in standard @command{install} programs, there is no reason to use @code{AC_PROG_INSTALL}; just put the file name of your program into your @file{Makefile.in} files. @end defmac @defmac AC_PROG_MKDIR_P @acindex{AC_PROG_MKDIR_P} @ovindex MKDIR_P Set output variable @code{MKDIR_P} to a program that ensures that for each argument, a directory named by this argument exists, creating it and its parent directories if needed, and without race conditions when two instances of the program attempt to make the same directory at nearly the same time. This macro uses the @samp{mkdir -p} command if possible. Otherwise, it falls back on invoking @command{install-sh} with the @option{-d} option, so your package should contain @file{install-sh} as described under @code{AC_PROG_INSTALL}. An @file{install-sh} file that predates Autoconf 2.60 or Automake 1.10 is vulnerable to race conditions, so if you want to support parallel installs from different packages into the same directory you need to make sure you have an up-to-date @file{install-sh}. In particular, be careful about using @samp{autoreconf -if} if your Automake predates Automake 1.10. This macro is related to the @code{AS_MKDIR_P} macro (@pxref{Programming in M4sh}), but it sets an output variable intended for use in other files, whereas @code{AS_MKDIR_P} is intended for use in scripts like @command{configure}. Also, @code{AS_MKDIR_P} does not accept options, but @code{MKDIR_P} supports the @option{-m} option, e.g., a makefile might invoke @code{$(MKDIR_P) -m 0 dir} to create an inaccessible directory, and conversely a makefile should use @code{$(MKDIR_P) -- $(FOO)} if @var{FOO} might yield a value that begins with @samp{-}. Finally, @code{AS_MKDIR_P} does not check for race condition vulnerability, whereas @code{AC_PROG_MKDIR_P} does. @samp{@@MKDIR_P@@} is special, as its value may vary for different configuration files. @end defmac @defmac AC_PROG_LEX @acindex{PROG_LEX} @ovindex LEX @ovindex LEXLIB @cvindex YYTEXT_POINTER @ovindex LEX_OUTPUT_ROOT If @code{flex} is found, set output variable @code{LEX} to @samp{flex} and @code{LEXLIB} to @option{-lfl}, if that library is in a standard place. Otherwise set @code{LEX} to @samp{lex} and @code{LEXLIB} to @option{-ll}. Define @code{YYTEXT_POINTER} if @code{yytext} defaults to @samp{char *} instead of to @samp{char []}. Also set output variable @code{LEX_OUTPUT_ROOT} to the base of the file name that the lexer generates; usually @file{lex.yy}, but sometimes something else. These results vary according to whether @code{lex} or @code{flex} is being used. You are encouraged to use Flex in your sources, since it is both more pleasant to use than plain Lex and the C source it produces is portable. In order to ensure portability, however, you must either provide a function @code{yywrap} or, if you don't use it (e.g., your scanner has no @samp{#include}-like feature), simply include a @samp{%noyywrap} statement in the scanner's source. Once this done, the scanner is portable (unless @emph{you} felt free to use nonportable constructs) and does not depend on any library. In this case, and in this case only, it is suggested that you use this Autoconf snippet: @example AC_PROG_LEX if test "$LEX" != flex; then LEX="$SHELL $missing_dir/missing flex" AC_SUBST([LEX_OUTPUT_ROOT], [lex.yy]) AC_SUBST([LEXLIB], ['']) fi @end example The shell script @command{missing} can be found in the Automake distribution. To ensure backward compatibility, Automake's @code{AM_PROG_LEX} invokes (indirectly) this macro twice, which causes an annoying but benign ``@code{AC_PROG_LEX} invoked multiple times'' warning. Future versions of Automake will fix this issue; meanwhile, just ignore this message. As part of running the test, this macro may delete any file in the configuration directory named @file{lex.yy.c} or @file{lexyy.c}. @end defmac @defmac AC_PROG_LN_S @acindex{PROG_LN_S} @ovindex LN_S If @samp{ln -s} works on the current file system (the operating system and file system support symbolic links), set the output variable @code{LN_S} to @samp{ln -s}; otherwise, if @samp{ln} works, set @code{LN_S} to @samp{ln}, and otherwise set it to @samp{cp -p}. If you make a link in a directory other than the current directory, its meaning depends on whether @samp{ln} or @samp{ln -s} is used. To safely create links using @samp{$(LN_S)}, either find out which form is used and adjust the arguments, or always invoke @code{ln} in the directory where the link is to be created. In other words, it does not work to do: @example $(LN_S) foo /x/bar @end example Instead, do: @example (cd /x && $(LN_S) foo bar) @end example @end defmac @defmac AC_PROG_RANLIB @acindex{PROG_RANLIB} @ovindex RANLIB Set output variable @code{RANLIB} to @samp{ranlib} if @code{ranlib} is found, and otherwise to @samp{:} (do nothing). @end defmac @defmac AC_PROG_SED @acindex{PROG_SED} @ovindex SED Set output variable @code{SED} to a Sed implementation that conforms to Posix and does not have arbitrary length limits. Report an error if no acceptable Sed is found. @xref{Limitations of Usual Tools}, for more information about portability problems with Sed. @end defmac @defmac AC_PROG_YACC @acindex{PROG_YACC} @ovindex YACC If @code{bison} is found, set output variable @code{YACC} to @samp{bison -y}. Otherwise, if @code{byacc} is found, set @code{YACC} to @samp{byacc}. Otherwise set @code{YACC} to @samp{yacc}. @end defmac @node Generic Programs @subsection Generic Program and File Checks These macros are used to find programs not covered by the ``particular'' test macros. If you need to check the behavior of a program as well as find out whether it is present, you have to write your own test for it (@pxref{Writing Tests}). By default, these macros use the environment variable @env{PATH}. If you need to check for a program that might not be in the user's @env{PATH}, you can pass a modified path to use instead, like this: @example AC_PATH_PROG([INETD], [inetd], [/usr/libexec/inetd], [$PATH:/usr/libexec:/usr/sbin:/usr/etc:/etc]) @end example You are strongly encouraged to declare the @var{variable} passed to @code{AC_CHECK_PROG} etc.@: as precious, @xref{Setting Output Variables}, @code{AC_ARG_VAR}, for more details. @defmac AC_CHECK_PROG (@var{variable}, @var{prog-to-check-for}, @var{value-if-found}, @ovar{value-if-not-found}, @ovar{path}, @ovar{reject}) @acindex{CHECK_PROG} Check whether program @var{prog-to-check-for} exists in @env{PATH}. If it is found, set @var{variable} to @var{value-if-found}, otherwise to @var{value-if-not-found}, if given. Always pass over @var{reject} (an absolute file name) even if it is the first found in the search path; in that case, set @var{variable} using the absolute file name of the @var{prog-to-check-for} found that is not @var{reject}. If @var{variable} was already set, do nothing. Calls @code{AC_SUBST} for @var{variable}. @end defmac @defmac AC_CHECK_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{CHECK_PROGS} Check for each program in the blank-separated list @var{progs-to-check-for} existing in the @env{PATH}. If one is found, set @var{variable} to the name of that program. Otherwise, continue checking the next program in the list. If none of the programs in the list are found, set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found} is not specified, the value of @var{variable} is not changed. Calls @code{AC_SUBST} for @var{variable}. @end defmac @defmac AC_CHECK_TARGET_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{CHECK_TARGET_TOOL} Like @code{AC_CHECK_PROG}, but first looks for @var{prog-to-check-for} with a prefix of the target type as determined by @code{AC_CANONICAL_TARGET}, followed by a dash (@pxref{Canonicalizing}). If the tool cannot be found with a prefix, and if the build and target types are equal, then it is also searched for without a prefix. As noted in @ref{Specifying Names, , Specifying the system type}, the target is rarely specified, because most of the time it is the same as the host: it is the type of system for which any compiler tool in the package produces code. What this macro looks for is, for example, @emph{a tool @r{(assembler, linker, etc.)}@: that the compiler driver @r{(@command{gcc} for the @acronym{GNU} C Compiler)} uses to produce objects, archives or executables}. @end defmac @defmac AC_CHECK_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{CHECK_TOOL} Like @code{AC_CHECK_PROG}, but first looks for @var{prog-to-check-for} with a prefix of the host type as determined by @code{AC_CANONICAL_HOST}, followed by a dash (@pxref{Canonicalizing}). For example, if the user runs @samp{configure --host=i386-gnu}, then this call: @example AC_CHECK_TOOL([RANLIB], [ranlib], [:]) @end example @noindent sets @code{RANLIB} to @file{i386-gnu-ranlib} if that program exists in @env{PATH}, or otherwise to @samp{ranlib} if that program exists in @env{PATH}, or to @samp{:} if neither program exists. In the future, when cross-compiling this macro will @emph{only} accept program names that are prefixed with the host type. For more information, see @ref{Specifying Names, , Specifying the system type}. @end defmac @defmac AC_CHECK_TARGET_TOOLS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{CHECK_TARGET_TOOLS} Like @code{AC_CHECK_TARGET_TOOL}, each of the tools in the list @var{progs-to-check-for} are checked with a prefix of the target type as determined by @code{AC_CANONICAL_TARGET}, followed by a dash (@pxref{Canonicalizing}). If none of the tools can be found with a prefix, and if the build and target types are equal, then the first one without a prefix is used. If a tool is found, set @var{variable} to the name of that program. If none of the tools in the list are found, set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found} is not specified, the value of @var{variable} is not changed. Calls @code{AC_SUBST} for @var{variable}. @end defmac @defmac AC_CHECK_TOOLS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{CHECK_TOOLS} Like @code{AC_CHECK_TOOL}, each of the tools in the list @var{progs-to-check-for} are checked with a prefix of the host type as determined by @code{AC_CANONICAL_HOST}, followed by a dash (@pxref{Canonicalizing}). If none of the tools can be found with a prefix, then the first one without a prefix is used. If a tool is found, set @var{variable} to the name of that program. If none of the tools in the list are found, set @var{variable} to @var{value-if-not-found}; if @var{value-if-not-found} is not specified, the value of @var{variable} is not changed. Calls @code{AC_SUBST} for @var{variable}. In the future, when cross-compiling this macro will @emph{not} accept program names that are not prefixed with the host type. @end defmac @defmac AC_PATH_PROG (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{PATH_PROG} Like @code{AC_CHECK_PROG}, but set @var{variable} to the absolute name of @var{prog-to-check-for} if found. @end defmac @defmac AC_PATH_PROGS (@var{variable}, @var{progs-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{PATH_PROGS} Like @code{AC_CHECK_PROGS}, but if any of @var{progs-to-check-for} are found, set @var{variable} to the absolute name of the program found. @end defmac @defmac AC_PATH_TARGET_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{PATH_TARGET_TOOL} Like @code{AC_CHECK_TARGET_TOOL}, but set @var{variable} to the absolute name of the program if it is found. @end defmac @defmac AC_PATH_TOOL (@var{variable}, @var{prog-to-check-for}, @ovar{value-if-not-found}, @ovar{path}) @acindex{PATH_TOOL} Like @code{AC_CHECK_TOOL}, but set @var{variable} to the absolute name of the program if it is found. In the future, when cross-compiling this macro will @emph{not} accept program names that are not prefixed with the host type. @end defmac @node Files @section Files @cindex File, checking You might also need to check for the existence of files. Before using these macros, ask yourself whether a runtime test might not be a better solution. Be aware that, like most Autoconf macros, they test a feature of the host machine, and therefore, they die when cross-compiling. @defmac AC_CHECK_FILE (@var{file}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{CHECK_FILE} Check whether file @var{file} exists on the native system. If it is found, execute @var{action-if-found}, otherwise do @var{action-if-not-found}, if given. @end defmac @defmac AC_CHECK_FILES (@var{files}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{CHECK_FILES} Executes @code{AC_CHECK_FILE} once for each file listed in @var{files}. Additionally, defines @samp{HAVE_@var{file}} (@pxref{Standard Symbols}) for each file found. @end defmac @node Libraries @section Library Files @cindex Library, checking The following macros check for the presence of certain C, C++, or Fortran library archive files. @defmac AC_CHECK_LIB (@var{library}, @var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries}) @acindex{CHECK_LIB} Test whether the library @var{library} is available by trying to link a test program that calls function @var{function} with the library. @var{function} should be a function provided by the library. Use the base name of the library; e.g., to check for @option{-lmp}, use @samp{mp} as the @var{library} argument. @var{action-if-found} is a list of shell commands to run if the link with the library succeeds; @var{action-if-not-found} is a list of shell commands to run if the link fails. If @var{action-if-found} is not specified, the default action prepends @option{-l@var{library}} to @code{LIBS} and defines @samp{HAVE_LIB@var{library}} (in all capitals). This macro is intended to support building @code{LIBS} in a right-to-left (least-dependent to most-dependent) fashion such that library dependencies are satisfied as a natural side effect of consecutive tests. Linkers are sensitive to library ordering so the order in which @code{LIBS} is generated is important to reliable detection of libraries. If linking with @var{library} results in unresolved symbols that would be resolved by linking with additional libraries, give those libraries as the @var{other-libraries} argument, separated by spaces: e.g., @option{-lXt -lX11}. Otherwise, this macro fails to detect that @var{library} is present, because linking the test program always fails with unresolved symbols. The @var{other-libraries} argument should be limited to cases where it is desirable to test for one library in the presence of another that is not already in @code{LIBS}. @code{AC_CHECK_LIB} requires some care in usage, and should be avoided in some common cases. Many standard functions like @code{gethostbyname} appear the standard C library on some hosts, and in special libraries like @code{nsl} on other hosts. On some hosts the special libraries contain variant implementations that you may not want to use. These days it is normally better to use @code{AC_SEARCH_LIBS([gethostbyname], [nsl])} instead of @code{AC_CHECK_LIB([nsl], [gethostbyname])}. @end defmac @defmac AC_SEARCH_LIBS (@var{function}, @var{search-libs}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries}) @acindex{SEARCH_LIBS} Search for a library defining @var{function} if it's not already available. This equates to calling @samp{AC_LINK_IFELSE([AC_LANG_CALL([], [@var{function}])])} first with no libraries, then for each library listed in @var{search-libs}. Add @option{-l@var{library}} to @code{LIBS} for the first library found to contain @var{function}, and run @var{action-if-found}. If the function is not found, run @var{action-if-not-found}. If linking with @var{library} results in unresolved symbols that would be resolved by linking with additional libraries, give those libraries as the @var{other-libraries} argument, separated by spaces: e.g., @option{-lXt -lX11}. Otherwise, this macro fails to detect that @var{function} is present, because linking the test program always fails with unresolved symbols. @end defmac @node Library Functions @section Library Functions The following macros check for particular C library functions. If there is no macro specifically defined to check for a function you need, and you don't need to check for any special properties of it, then you can use one of the general function-check macros. @menu * Function Portability:: Pitfalls with usual functions * Particular Functions:: Special handling to find certain functions * Generic Functions:: How to find other functions @end menu @node Function Portability @subsection Portability of C Functions @cindex Portability of C functions @cindex C function portability Most usual functions can either be missing, or be buggy, or be limited on some architectures. This section tries to make an inventory of these portability issues. By definition, this list always requires additions. Please help us keeping it as complete as possible. @table @asis @item @code{exit} @c @fuindex exit @prindex @code{exit} On ancient hosts, @code{exit} returned @code{int}. This is because @code{exit} predates @code{void}, and there was a long tradition of it returning @code{int}. On current hosts, the problem more likely is that @code{exit} is not declared, due to C++ problems of some sort or another. For this reason we suggest that test programs not invoke @code{exit}, but return from @code{main} instead. @item @code{free} @c @fuindex free @prindex @code{free} The C standard says a call @code{free (NULL)} does nothing, but some old systems don't support this (e.g., NextStep). @item @code{isinf} @itemx @code{isnan} @c @fuindex isinf @c @fuindex isnan @prindex @code{isinf} @prindex @code{isnan} The C99 standard says that @code{isinf} and @code{isnan} are macros. On some systems just macros are available (e.g., @acronym{HP-UX} and Solaris 10), on some systems both macros and functions (e.g., glibc 2.3.2), and on some systems only functions (e.g., IRIX 6 and Solaris 9). In some cases these functions are declared in nonstandard headers like @code{} and defined in non-default libraries like @option{-lm} or @option{-lsunmath}. The C99 @code{isinf} and @code{isnan} macros work correctly with @code{long double} arguments, but pre-C99 systems that use functions typically assume @code{double} arguments. On such a system, @code{isinf} incorrectly returns true for a finite @code{long double} argument that is outside the range of @code{double}. To work around this porting mess, you can use code like the following. @smallexample #include #ifndef isnan # define isnan(x) \ (sizeof (x) == sizeof (long double) ? isnan_ld (x) \ : sizeof (x) == sizeof (double) ? isnan_d (x) \ : isnan_f (x)) static inline int isnan_f (float x) @{ return x != x; @} static inline int isnan_d (double x) @{ return x != x; @} static inline int isnan_ld (long double x) @{ return x != x; @} #endif #ifndef isinf # define isinf(x) \ (sizeof (x) == sizeof (long double) ? isinf_ld (x) \ : sizeof (x) == sizeof (double) ? isinf_d (x) \ : isinf_f (x)) static inline int isinf_f (float x) @{ return isnan (x - x); @} static inline int isinf_d (double x) @{ return isnan (x - x); @} static inline int isinf_ld (long double x) @{ return isnan (x - x); @} #endif @end smallexample Use @code{AC_C_INLINE} (@pxref{C Compiler}) so that this code works on compilers that lack the @code{inline} keyword. Some optimizing compilers mishandle these definitions, but systems with that bug typically have missing or broken @code{isnan} functions anyway, so it's probably not worth worrying about. @item @code{malloc} @c @fuindex malloc @prindex @code{malloc} The C standard says a call @code{malloc (0)} is implementation dependent. It can return either @code{NULL} or a new non-null pointer. The latter is more common (e.g., the @acronym{GNU} C Library) but is by no means universal. @code{AC_FUNC_MALLOC} can be used to insist on non-@code{NULL} (@pxref{Particular Functions}). @item @code{putenv} @c @fuindex putenv @prindex @code{putenv} Posix prefers @code{setenv} to @code{putenv}; among other things, @code{putenv} is not required of all Posix implementations, but @code{setenv} is. Posix specifies that @code{putenv} puts the given string directly in @code{environ}, but some systems make a copy of it instead (e.g., glibc 2.0, or @acronym{BSD}). And when a copy is made, @code{unsetenv} might not free it, causing a memory leak (e.g., Free@acronym{BSD} 4). On some systems @code{putenv ("FOO")} removes @samp{FOO} from the environment, but this is not standard usage and it dumps core on some systems (e.g., AIX). On MinGW, a call @code{putenv ("FOO=")} removes @samp{FOO} from the environment, rather than inserting it with an empty value. @item @code{realloc} @c @fuindex realloc @prindex @code{realloc} The C standard says a call @code{realloc (NULL, size)} is equivalent to @code{malloc (size)}, but some old systems don't support this (e.g., NextStep). @item @code{signal} handler @c @fuindex signal @prindex @code{signal} Normally @code{signal} takes a handler function with a return type of @code{void}, but some old systems required @code{int} instead. Any actual @code{int} value returned is not used; this is only a difference in the function prototype demanded. All systems we know of in current use return @code{void}. The @code{int} was to support K&R C, where of course @code{void} is not available. @code{AC_TYPE_SIGNAL} (@pxref{Particular Types}) can be used to establish the correct type in all cases. @item @code{snprintf} @c @fuindex snprintf @prindex @code{snprintf} @c @fuindex vsnprintf @prindex @code{vsnprintf} The C99 standard says that if the output array isn't big enough and if no other errors occur, @code{snprintf} and @code{vsnprintf} truncate the output and return the number of bytes that ought to have been produced. Some older systems return the truncated length (e.g., @acronym{GNU} C Library 2.0.x or @sc{irix} 6.5), some a negative value (e.g., earlier @acronym{GNU} C Library versions), and some the buffer length without truncation (e.g., 32-bit Solaris 7). Also, some buggy older systems ignore the length and overrun the buffer (e.g., 64-bit Solaris 7). @item @code{sprintf} @c @fuindex sprintf @prindex @code{sprintf} @c @fuindex vsprintf @prindex @code{vsprintf} The C standard says @code{sprintf} and @code{vsprintf} return the number of bytes written. On some ancient systems (SunOS 4 for instance) they return the buffer pointer instead, but these no longer need to be worried about. @item @code{sscanf} @c @fuindex sscanf @prindex @code{sscanf} On various old systems, e.g., @acronym{HP-UX} 9, @code{sscanf} requires that its input string be writable (though it doesn't actually change it). This can be a problem when using @command{gcc} since it normally puts constant strings in read-only memory (@pxref{Incompatibilities, Incompatibilities of @acronym{GCC}, , gcc, Using and Porting the @acronym{GNU} Compiler Collection}). Apparently in some cases even having format strings read-only can be a problem. @item @code{strerror_r} @c @fuindex strerror_r @prindex @code{strerror_r} Posix specifies that @code{strerror_r} returns an @code{int}, but many systems (e.g., @acronym{GNU} C Library version 2.2.4) provide a different version returning a @code{char *}. @code{AC_FUNC_STRERROR_R} can detect which is in use (@pxref{Particular Functions}). @item @code{strnlen} @c @fuindex strnlen @prindex @code{strnlen} @acronym{AIX} 4.3 provides a broken version which produces the following results: @example strnlen ("foobar", 0) = 0 strnlen ("foobar", 1) = 3 strnlen ("foobar", 2) = 2 strnlen ("foobar", 3) = 1 strnlen ("foobar", 4) = 0 strnlen ("foobar", 5) = 6 strnlen ("foobar", 6) = 6 strnlen ("foobar", 7) = 6 strnlen ("foobar", 8) = 6 strnlen ("foobar", 9) = 6 @end example @item @code{sysconf} @c @fuindex sysconf @prindex @code{sysconf} @code{_SC_PAGESIZE} is standard, but some older systems (e.g., @acronym{HP-UX} 9) have @code{_SC_PAGE_SIZE} instead. This can be tested with @code{#ifdef}. @item @code{unlink} @c @fuindex unlink @prindex @code{unlink} The Posix spec says that @code{unlink} causes the given file to be removed only after there are no more open file handles for it. Some non-Posix hosts have trouble with this requirement, though, and some @acronym{DOS} variants even corrupt the file system. @item @code{unsetenv} @c @fuindex unsetenv @prindex @code{unsetenv} On MinGW, @code{unsetenv} is not available, but a variable @samp{FOO} can be removed with a call @code{putenv ("FOO=")}, as described under @code{putenv} above. @item @code{va_copy} @c @fuindex va_copy @prindex @code{va_copy} The C99 standard provides @code{va_copy} for copying @code{va_list} variables. It may be available in older environments too, though possibly as @code{__va_copy} (e.g., @command{gcc} in strict pre-C99 mode). These can be tested with @code{#ifdef}. A fallback to @code{memcpy (&dst, &src, sizeof (va_list))} gives maximum portability. @item @code{va_list} @c @fuindex va_list @prindex @code{va_list} @code{va_list} is not necessarily just a pointer. It can be a @code{struct} (e.g., @command{gcc} on Alpha), which means @code{NULL} is not portable. Or it can be an array (e.g., @command{gcc} in some PowerPC configurations), which means as a function parameter it can be effectively call-by-reference and library routines might modify the value back in the caller (e.g., @code{vsnprintf} in the @acronym{GNU} C Library 2.1). @item Signed @code{>>} Normally the C @code{>>} right shift of a signed type replicates the high bit, giving a so-called ``arithmetic'' shift. But care should be taken since Standard C doesn't require that behavior. On those few processors without a native arithmetic shift (for instance Cray vector systems) zero bits may be shifted in, the same as a shift of an unsigned type. @item Integer @code{/} C divides signed integers by truncating their quotient toward zero, yielding the same result as Fortran. However, before C99 the standard allowed C implementations to take the floor or ceiling of the quotient in some cases. Hardly any implementations took advantage of this freedom, though, and it's probably not worth worrying about this issue nowadays. @end table @node Particular Functions @subsection Particular Function Checks @cindex Function, checking These macros check for particular C functions---whether they exist, and in some cases how they respond when given certain arguments. @defmac AC_FUNC_ALLOCA @acindex{FUNC_ALLOCA} @cvindex C_ALLOCA @cvindex HAVE_ALLOCA_H @ovindex ALLOCA @c @fuindex alloca @prindex @code{alloca} @hdrindex{alloca.h} Check how to get @code{alloca}. Tries to get a builtin version by checking for @file{alloca.h} or the predefined C preprocessor macros @code{__GNUC__} and @code{_AIX}. If this macro finds @file{alloca.h}, it defines @code{HAVE_ALLOCA_H}. If those attempts fail, it looks for the function in the standard C library. If any of those methods succeed, it defines @code{HAVE_ALLOCA}. Otherwise, it sets the output variable @code{ALLOCA} to @samp{$@{LIBOBJDIR@}alloca.o} and defines @code{C_ALLOCA} (so programs can periodically call @samp{alloca (0)} to garbage collect). This variable is separate from @code{LIBOBJS} so multiple programs can share the value of @code{ALLOCA} without needing to create an actual library, in case only some of them use the code in @code{LIBOBJS}. The @samp{$@{LIBOBJDIR@}} prefix serves the same purpose as in @code{LIBOBJS} (@pxref{AC_LIBOBJ vs LIBOBJS}). This macro does not try to get @code{alloca} from the System V R3 @file{libPW} or the System V R4 @file{libucb} because those libraries contain some incompatible functions that cause trouble. Some versions do not even contain @code{alloca} or contain a buggy version. If you still want to use their @code{alloca}, use @code{ar} to extract @file{alloca.o} from them instead of compiling @file{alloca.c}. Source files that use @code{alloca} should start with a piece of code like the following, to declare it properly. @example @group #ifdef HAVE_ALLOCA_H # include #elif defined __GNUC__ # define alloca __builtin_alloca #elif defined _AIX # define alloca __alloca #elif defined _MSC_VER # include # define alloca _alloca #else # include # ifdef __cplusplus extern "C" # endif void *alloca (size_t); #endif @end group @end example @end defmac @defmac AC_FUNC_CHOWN @acindex{FUNC_CHOWN} @c @fuindex chown @prindex @code{chown} If the @code{chown} function is available and works (in particular, it should accept @option{-1} for @code{uid} and @code{gid}), define @code{HAVE_CHOWN}. @end defmac @defmac AC_FUNC_CLOSEDIR_VOID @acindex{FUNC_CLOSEDIR_VOID} @cvindex CLOSEDIR_VOID @c @fuindex closedir @prindex @code{closedir} If the @code{closedir} function does not return a meaningful value, define @code{CLOSEDIR_VOID}. Otherwise, callers ought to check its return value for an error indicator. Currently this test is implemented by running a test program. When cross compiling the pessimistic assumption that @code{closedir} does not return a meaningful value is made. This macro is obsolescent, as @code{closedir} returns a meaningful value on current systems. New programs need not use this macro. @end defmac @defmac AC_FUNC_ERROR_AT_LINE @acindex{FUNC_ERROR_AT_LINE} @c @fuindex error_at_line @prindex @code{error_at_line} If the @code{error_at_line} function is not found, require an @code{AC_LIBOBJ} replacement of @samp{error}. @end defmac @defmac AC_FUNC_FNMATCH @acindex{FUNC_FNMATCH} @c @fuindex fnmatch @prindex @code{fnmatch} If the @code{fnmatch} function conforms to Posix, define @code{HAVE_FNMATCH}. Detect common implementation bugs, for example, the bugs in Solaris 2.4. Unlike the other specific @code{AC_FUNC} macros, @code{AC_FUNC_FNMATCH} does not replace a broken/missing @code{fnmatch}. This is for historical reasons. See @code{AC_REPLACE_FNMATCH} below. This macro is obsolescent. New programs should use Gnulib's @code{fnmatch-posix} module. @xref{Gnulib}. @end defmac @defmac AC_FUNC_FNMATCH_GNU @acindex{FUNC_FNMATCH_GNU} @c @fuindex fnmatch @prindex @code{fnmatch} Behave like @code{AC_REPLACE_FNMATCH} (@emph{replace}) but also test whether @code{fnmatch} supports @acronym{GNU} extensions. Detect common implementation bugs, for example, the bugs in the @acronym{GNU} C Library 2.1. This macro is obsolescent. New programs should use Gnulib's @code{fnmatch-gnu} module. @xref{Gnulib}. @end defmac @defmac AC_FUNC_FORK @acindex{FUNC_FORK} @cvindex HAVE_VFORK_H @cvindex HAVE_WORKING_FORK @cvindex HAVE_WORKING_VFORK @cvindex vfork @c @fuindex fork @prindex @code{fork} @c @fuindex vfork @prindex @code{vfork} @hdrindex{vfork.h} This macro checks for the @code{fork} and @code{vfork} functions. If a working @code{fork} is found, define @code{HAVE_WORKING_FORK}. This macro checks whether @code{fork} is just a stub by trying to run it. If @file{vfork.h} is found, define @code{HAVE_VFORK_H}. If a working @code{vfork} is found, define @code{HAVE_WORKING_VFORK}. Otherwise, define @code{vfork} to be @code{fork} for backward compatibility with previous versions of @command{autoconf}. This macro checks for several known errors in implementations of @code{vfork} and considers the system to not have a working @code{vfork} if it detects any of them. It is not considered to be an implementation error if a child's invocation of @code{signal} modifies the parent's signal handler, since child processes rarely change their signal handlers. Since this macro defines @code{vfork} only for backward compatibility with previous versions of @command{autoconf} you're encouraged to define it yourself in new code: @example @group #ifndef HAVE_WORKING_VFORK # define vfork fork #endif @end group @end example @end defmac @defmac AC_FUNC_FSEEKO @acindex{FUNC_FSEEKO} @cvindex _LARGEFILE_SOURCE @c @fuindex fseeko @prindex @code{fseeko} If the @code{fseeko} function is available, define @code{HAVE_FSEEKO}. Define @code{_LARGEFILE_SOURCE} if necessary to make the prototype visible on some systems (e.g., glibc 2.2). Otherwise linkage problems may occur when compiling with @code{AC_SYS_LARGEFILE} on largefile-sensitive systems where @code{off_t} does not default to a 64bit entity. @end defmac @defmac AC_FUNC_GETGROUPS @acindex{FUNC_GETGROUPS} @ovindex GETGROUPS_LIBS @c @fuindex getgroups @prindex @code{getgroups} If the @code{getgroups} function is available and works (unlike on Ultrix 4.3, where @samp{getgroups (0, 0)} always fails), define @code{HAVE_GETGROUPS}. Set @code{GETGROUPS_LIBS} to any libraries needed to get that function. This macro runs @code{AC_TYPE_GETGROUPS}. @end defmac @defmac AC_FUNC_GETLOADAVG @acindex{FUNC_GETLOADAVG} @cvindex SVR4 @cvindex DGUX @cvindex UMAX @cvindex UMAX4_3 @cvindex HAVE_NLIST_H @cvindex NLIST_NAME_UNION @cvindex GETLODAVG_PRIVILEGED @cvindex NEED_SETGID @cvindex C_GETLOADAVG @ovindex LIBOBJS @ovindex NEED_SETGID @ovindex KMEM_GROUP @ovindex GETLOADAVG_LIBS @c @fuindex getloadavg @prindex @code{getloadavg} Check how to get the system load averages. To perform its tests properly, this macro needs the file @file{getloadavg.c}; therefore, be sure to set the @code{AC_LIBOBJ} replacement directory properly (see @ref{Generic Functions}, @code{AC_CONFIG_LIBOBJ_DIR}). If the system has the @code{getloadavg} function, define @code{HAVE_GETLOADAVG}, and set @code{GETLOADAVG_LIBS} to any libraries necessary to get that function. Also add @code{GETLOADAVG_LIBS} to @code{LIBS}. Otherwise, require an @code{AC_LIBOBJ} replacement for @samp{getloadavg} with source code in @file{@var{dir}/getloadavg.c}, and possibly define several other C preprocessor macros and output variables: @enumerate @item Define @code{C_GETLOADAVG}. @item Define @code{SVR4}, @code{DGUX}, @code{UMAX}, or @code{UMAX4_3} if on those systems. @item @hdrindex{nlist.h} If @file{nlist.h} is found, define @code{HAVE_NLIST_H}. @item If @samp{struct nlist} has an @samp{n_un.n_name} member, define @code{HAVE_STRUCT_NLIST_N_UN_N_NAME}. The obsolete symbol @code{NLIST_NAME_UNION} is still defined, but do not depend upon it. @item Programs may need to be installed set-group-ID (or set-user-ID) for @code{getloadavg} to work. In this case, define @code{GETLOADAVG_PRIVILEGED}, set the output variable @code{NEED_SETGID} to @samp{true} (and otherwise to @samp{false}), and set @code{KMEM_GROUP} to the name of the group that should own the installed program. @end enumerate The @code{AC_FUNC_GETLOADVG} macro is obsolescent. New programs should use Gnulib's @code{getloadavg} module. @xref{Gnulib}. @end defmac @defmac AC_FUNC_GETMNTENT @acindex{FUNC_GETMNTENT} @cvindex HAVE_GETMNTENT @c @fuindex getmntent @prindex @code{getmntent} Check for @code{getmntent} in the standard C library, and then in the @file{sun}, @file{seq}, and @file{gen} libraries, for @sc{unicos}, @sc{irix} 4, @sc{ptx}, and UnixWare, respectively. Then, if @code{getmntent} is available, define @code{HAVE_GETMNTENT}. @end defmac @defmac AC_FUNC_GETPGRP @acindex{FUNC_GETPGRP} @cvindex GETPGRP_VOID @c @fuindex getpgid @c @fuindex getpgrp @prindex @code{getpgid} @prindex @code{getpgrp} Define @code{GETPGRP_VOID} if it is an error to pass 0 to @code{getpgrp}; this is the Posix behavior. On older @acronym{BSD} systems, you must pass 0 to @code{getpgrp}, as it takes an argument and behaves like Posix's @code{getpgid}. @example #ifdef GETPGRP_VOID pid = getpgrp (); #else pid = getpgrp (0); #endif @end example This macro does not check whether @code{getpgrp} exists at all; if you need to work in that situation, first call @code{AC_CHECK_FUNC} for @code{getpgrp}. This macro is obsolescent, as current systems have a @code{getpgrp} whose signature conforms to Posix. New programs need not use this macro. @end defmac @defmac AC_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK @acindex{FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK} @cvindex LSTAT_FOLLOWS_SLASHED_SYMLINK @c @fuindex lstat @prindex @code{lstat} If @file{link} is a symbolic link, then @code{lstat} should treat @file{link/} the same as @file{link/.}. However, many older @code{lstat} implementations incorrectly ignore trailing slashes. It is safe to assume that if @code{lstat} incorrectly ignores trailing slashes, then other symbolic-link-aware functions like @code{unlink} also incorrectly ignore trailing slashes. If @code{lstat} behaves properly, define @code{LSTAT_FOLLOWS_SLASHED_SYMLINK}, otherwise require an @code{AC_LIBOBJ} replacement of @code{lstat}. @end defmac @defmac AC_FUNC_MALLOC @acindex{FUNC_MALLOC} @cvindex HAVE_MALLOC @cvindex malloc @c @fuindex malloc @prindex @code{malloc} If the @code{malloc} function is compatible with the @acronym{GNU} C library @code{malloc} (i.e., @samp{malloc (0)} returns a valid pointer), define @code{HAVE_MALLOC} to 1. Otherwise define @code{HAVE_MALLOC} to 0, ask for an @code{AC_LIBOBJ} replacement for @samp{malloc}, and define @code{malloc} to @code{rpl_malloc} so that the native @code{malloc} is not used in the main project. Typically, the replacement file @file{malloc.c} should look like (note the @samp{#undef malloc}): @verbatim #ifdef HAVE_CONFIG_H # include #endif #undef malloc #include void *malloc (); /* Allocate an N-byte block of memory from the heap. If N is zero, allocate a 1-byte block. */ void * rpl_malloc (size_t n) { if (n == 0) n = 1; return malloc (n); } @end verbatim @end defmac @defmac AC_FUNC_MEMCMP @acindex{FUNC_MEMCMP} @ovindex LIBOBJS @c @fuindex memcmp @prindex @code{memcmp} If the @code{memcmp} function is not available, or does not work on 8-bit data (like the one on SunOS 4.1.3), or fails when comparing 16 bytes or more and with at least one buffer not starting on a 4-byte boundary (such as the one on NeXT x86 OpenStep), require an @code{AC_LIBOBJ} replacement for @samp{memcmp}. This macro is obsolescent, as current systems have a working @code{memcmp}. New programs need not use this macro. @end defmac @defmac AC_FUNC_MBRTOWC @acindex{FUNC_MBRTOWC} @cvindex HAVE_MBRTOWC @c @fuindex mbrtowc @prindex @code{mbrtowc} Define @code{HAVE_MBRTOWC} to 1 if the function @code{mbrtowc} and the type @code{mbstate_t} are properly declared. @end defmac @defmac AC_FUNC_MKTIME @acindex{FUNC_MKTIME} @ovindex LIBOBJS @c @fuindex mktime @prindex @code{mktime} If the @code{mktime} function is not available, or does not work correctly, require an @code{AC_LIBOBJ} replacement for @samp{mktime}. For the purposes of this test, @code{mktime} should conform to the Posix standard and should be the inverse of @code{localtime}. @end defmac @defmac AC_FUNC_MMAP @acindex{FUNC_MMAP} @cvindex HAVE_MMAP @c @fuindex mmap @prindex @code{mmap} If the @code{mmap} function exists and works correctly, define @code{HAVE_MMAP}. This checks only private fixed mapping of already-mapped memory. @end defmac @defmac AC_FUNC_OBSTACK @acindex{FUNC_OBSTACK} @cvindex HAVE_OBSTACK @cindex obstack If the obstacks are found, define @code{HAVE_OBSTACK}, else require an @code{AC_LIBOBJ} replacement for @samp{obstack}. @end defmac @defmac AC_FUNC_REALLOC @acindex{FUNC_REALLOC} @cvindex HAVE_REALLOC @cvindex realloc @c @fuindex realloc @prindex @code{realloc} If the @code{realloc} function is compatible with the @acronym{GNU} C library @code{realloc} (i.e., @samp{realloc (NULL, 0)} returns a valid pointer), define @code{HAVE_REALLOC} to 1. Otherwise define @code{HAVE_REALLOC} to 0, ask for an @code{AC_LIBOBJ} replacement for @samp{realloc}, and define @code{realloc} to @code{rpl_realloc} so that the native @code{realloc} is not used in the main project. See @code{AC_FUNC_MALLOC} for details. @end defmac @defmac AC_FUNC_SELECT_ARGTYPES @acindex{FUNC_SELECT_ARGTYPES} @cvindex SELECT_TYPE_ARG1 @cvindex SELECT_TYPE_ARG234 @cvindex SELECT_TYPE_ARG5 @c @fuindex select @prindex @code{select} Determines the correct type to be passed for each of the @code{select} function's arguments, and defines those types in @code{SELECT_TYPE_ARG1}, @code{SELECT_TYPE_ARG234}, and @code{SELECT_TYPE_ARG5} respectively. @code{SELECT_TYPE_ARG1} defaults to @samp{int}, @code{SELECT_TYPE_ARG234} defaults to @samp{int *}, and @code{SELECT_TYPE_ARG5} defaults to @samp{struct timeval *}. This macro is obsolescent, as current systems have a @code{select} whose signature conforms to Posix. New programs need not use this macro. @end defmac @defmac AC_FUNC_SETPGRP @acindex{FUNC_SETPGRP} @cvindex SETPGRP_VOID @c @fuindex setpgrp @prindex @code{setpgrp} If @code{setpgrp} takes no argument (the Posix version), define @code{SETPGRP_VOID}. Otherwise, it is the @acronym{BSD} version, which takes two process IDs as arguments. This macro does not check whether @code{setpgrp} exists at all; if you need to work in that situation, first call @code{AC_CHECK_FUNC} for @code{setpgrp}. This macro is obsolescent, as current systems have a @code{setpgrp} whose signature conforms to Posix. New programs need not use this macro. @end defmac @defmac AC_FUNC_STAT @defmacx AC_FUNC_LSTAT @acindex{FUNC_STAT} @acindex{FUNC_LSTAT} @cvindex HAVE_STAT_EMPTY_STRING_BUG @cvindex HAVE_LSTAT_EMPTY_STRING_BUG @c @fuindex stat @prindex @code{stat} @c @fuindex lstat @prindex @code{lstat} Determine whether @code{stat} or @code{lstat} have the bug that it succeeds when given the zero-length file name as argument. The @code{stat} and @code{lstat} from SunOS 4.1.4 and the Hurd (as of 1998-11-01) do this. If it does, then define @code{HAVE_STAT_EMPTY_STRING_BUG} (or @code{HAVE_LSTAT_EMPTY_STRING_BUG}) and ask for an @code{AC_LIBOBJ} replacement of it. These macros are obsolescent, as no current systems have the bug. New programs need not use these macros. @end defmac @defmac AC_FUNC_SETVBUF_REVERSED @acindex{FUNC_SETVBUF_REVERSED} @cvindex SETVBUF_REVERSED @c @fuindex setvbuf @prindex @code{setvbuf} If @code{setvbuf} takes the buffering type as its second argument and the buffer pointer as the third, instead of the other way around, define @code{SETVBUF_REVERSED}. This macro is obsolescent, as no current systems have the bug. New programs need not use this macro. @end defmac @defmac AC_FUNC_STRCOLL @acindex{FUNC_STRCOLL} @cvindex HAVE_STRCOLL @c @fuindex strcoll @prindex @code{strcoll} If the @code{strcoll} function exists and works correctly, define @code{HAVE_STRCOLL}. This does a bit more than @samp{AC_CHECK_FUNCS(strcoll)}, because some systems have incorrect definitions of @code{strcoll} that should not be used. @end defmac @defmac AC_FUNC_STRERROR_R @acindex{FUNC_STRERROR_R} @cvindex HAVE_STRERROR_R @cvindex HAVE_DECL_STRERROR_R @cvindex STRERROR_R_CHAR_P @c @fuindex strerror_r @prindex @code{strerror_r} If @code{strerror_r} is available, define @code{HAVE_STRERROR_R}, and if it is declared, define @code{HAVE_DECL_STRERROR_R}. If it returns a @code{char *} message, define @code{STRERROR_R_CHAR_P}; otherwise it returns an @code{int} error number. The Thread-Safe Functions option of Posix requires @code{strerror_r} to return @code{int}, but many systems (including, for example, version 2.2.4 of the @acronym{GNU} C Library) return a @code{char *} value that is not necessarily equal to the buffer argument. @end defmac @defmac AC_FUNC_STRFTIME @acindex{FUNC_STRFTIME} @cvindex HAVE_STRFTIME @c @fuindex strftime @prindex @code{strftime} Check for @code{strftime} in the @file{intl} library, for SCO Unix. Then, if @code{strftime} is available, define @code{HAVE_STRFTIME}. This macro is obsolescent, as no current systems require the @file{intl} library for @code{strftime}. New programs need not use this macro. @end defmac @defmac AC_FUNC_STRTOD @acindex{FUNC_STRTOD} @ovindex POW_LIB @c @fuindex strtod @prindex @code{strtod} If the @code{strtod} function does not exist or doesn't work correctly, ask for an @code{AC_LIBOBJ} replacement of @samp{strtod}. In this case, because @file{strtod.c} is likely to need @samp{pow}, set the output variable @code{POW_LIB} to the extra library needed. @end defmac @defmac AC_FUNC_STRTOLD @acindex{FUNC_STRTOLD} @prindex @code{strtold} If the @code{strtold} function exists and conforms to C99, define @code{HAVE_STRTOLD}. @end defmac @defmac AC_FUNC_STRNLEN @acindex{FUNC_STRNLEN} @cvindex HAVE_STRNLEN @c @fuindex strnlen @prindex @code{strnlen} If the @code{strnlen} function is not available, or is buggy (like the one from @acronym{AIX} 4.3), require an @code{AC_LIBOBJ} replacement for it. @end defmac @defmac AC_FUNC_UTIME_NULL @acindex{FUNC_UTIME_NULL} @cvindex HAVE_UTIME_NULL @c @fuindex utime @prindex @code{utime} If @samp{utime (@var{file}, NULL)} sets @var{file}'s timestamp to the present, define @code{HAVE_UTIME_NULL}. This macro is obsolescent, as all current systems have a @code{utime} that behaves this way. New programs need not use this macro. @end defmac @defmac AC_FUNC_VPRINTF @acindex{FUNC_VPRINTF} @cvindex HAVE_VPRINTF @cvindex HAVE_DOPRNT @c @fuindex vprintf @prindex @code{vprintf} If @code{vprintf} is found, define @code{HAVE_VPRINTF}. Otherwise, if @code{_doprnt} is found, define @code{HAVE_DOPRNT}. (If @code{vprintf} is available, you may assume that @code{vfprintf} and @code{vsprintf} are also available.) This macro is obsolescent, as all current systems have @code{vprintf}. New programs need not use this macro. @end defmac @defmac AC_REPLACE_FNMATCH @acindex{REPLACE_FNMATCH} @c @fuindex fnmatch @prindex @code{fnmatch} @hdrindex{fnmatch.h} If the @code{fnmatch} function does not conform to Posix (see @code{AC_FUNC_FNMATCH}), ask for its @code{AC_LIBOBJ} replacement. The files @file{fnmatch.c}, @file{fnmatch_loop.c}, and @file{fnmatch_.h} in the @code{AC_LIBOBJ} replacement directory are assumed to contain a copy of the source code of @acronym{GNU} @code{fnmatch}. If necessary, this source code is compiled as an @code{AC_LIBOBJ} replacement, and the @file{fnmatch_.h} file is linked to @file{fnmatch.h} so that it can be included in place of the system @code{}. This macro is obsolescent, as it assumes the use of particular source files. New programs should use Gnulib's @code{fnmatch-posix} module, which provides this macro along with the source files. @xref{Gnulib}. @end defmac @node Generic Functions @subsection Generic Function Checks These macros are used to find functions not covered by the ``particular'' test macros. If the functions might be in libraries other than the default C library, first call @code{AC_CHECK_LIB} for those libraries. If you need to check the behavior of a function as well as find out whether it is present, you have to write your own test for it (@pxref{Writing Tests}). @defmac AC_CHECK_FUNC (@var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{CHECK_FUNC} If C function @var{function} is available, run shell commands @var{action-if-found}, otherwise @var{action-if-not-found}. If you just want to define a symbol if the function is available, consider using @code{AC_CHECK_FUNCS} instead. This macro checks for functions with C linkage even when @code{AC_LANG(C++)} has been called, since C is more standardized than C++. (@pxref{Language Choice}, for more information about selecting the language for checks.) @end defmac @defmac AC_CHECK_FUNCS (@var{function}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{CHECK_FUNCS} @cvindex HAVE_@var{function} For each @var{function} enumerated in the blank-or-newline-separated argument list, define @code{HAVE_@var{function}} (in all capitals) if it is available. If @var{action-if-found} is given, it is additional shell code to execute when one of the functions is found. You can give it a value of @samp{break} to break out of the loop on the first match. If @var{action-if-not-found} is given, it is executed when one of the functions is not found. @end defmac @defmac AC_CHECK_FUNCS_ONCE (@var{function}@dots{}) @acindex{CHECK_FUNCS_ONCE} @cvindex HAVE_@var{function} For each @var{function} enumerated in the blank-or-newline-separated argument list, define @code{HAVE_@var{function}} (in all capitals) if it is available. This is a once-only variant of @code{AC_CHECK_FUNCS}. It generates the checking code at most once, so that @command{configure} is smaller and faster; but the checks cannot be conditionalized and are always done once, early during the @command{configure} run. @end defmac @sp 1 Autoconf follows a philosophy that was formed over the years by those who have struggled for portability: isolate the portability issues in specific files, and then program as if you were in a Posix environment. Some functions may be missing or unfixable, and your package must be ready to replace them. Suitable replacements for many such problem functions are available from Gnulib (@pxref{Gnulib}). @defmac AC_LIBOBJ (@var{function}) @acindex{LIBOBJ} @ovindex LIBOBJS Specify that @samp{@var{function}.c} must be included in the executables to replace a missing or broken implementation of @var{function}. Technically, it adds @samp{@var{function}.$ac_objext} to the output variable @code{LIBOBJS} if it is not already in, and calls @code{AC_LIBSOURCE} for @samp{@var{function}.c}. You should not directly change @code{LIBOBJS}, since this is not traceable. @end defmac @defmac AC_LIBSOURCE (@var{file}) @acindex{LIBSOURCE} Specify that @var{file} might be needed to compile the project. If you need to know what files might be needed by a @file{configure.ac}, you should trace @code{AC_LIBSOURCE}. @var{file} must be a literal. This macro is called automatically from @code{AC_LIBOBJ}, but you must call it explicitly if you pass a shell variable to @code{AC_LIBOBJ}. In that case, since shell variables cannot be traced statically, you must pass to @code{AC_LIBSOURCE} any possible files that the shell variable might cause @code{AC_LIBOBJ} to need. For example, if you want to pass a variable @code{$foo_or_bar} to @code{AC_LIBOBJ} that holds either @code{"foo"} or @code{"bar"}, you should do: @example AC_LIBSOURCE([foo.c]) AC_LIBSOURCE([bar.c]) AC_LIBOBJ([$foo_or_bar]) @end example @noindent There is usually a way to avoid this, however, and you are encouraged to simply call @code{AC_LIBOBJ} with literal arguments. Note that this macro replaces the obsolete @code{AC_LIBOBJ_DECL}, with slightly different semantics: the old macro took the function name, e.g., @code{foo}, as its argument rather than the file name. @end defmac @defmac AC_LIBSOURCES (@var{files}) @acindex{LIBSOURCES} Like @code{AC_LIBSOURCE}, but accepts one or more @var{files} in a comma-separated M4 list. Thus, the above example might be rewritten: @example AC_LIBSOURCES([foo.c, bar.c]) AC_LIBOBJ([$foo_or_bar]) @end example @end defmac @defmac AC_CONFIG_LIBOBJ_DIR (@var{directory}) @acindex{CONFIG_LIBOBJ_DIR} Specify that @code{AC_LIBOBJ} replacement files are to be found in @var{directory}, a name relative to the top level of the source tree. The replacement directory defaults to @file{.}, the top level directory, and the most typical value is @file{lib}, corresponding to @samp{AC_CONFIG_LIBOBJ_DIR([lib])}. @command{configure} might need to know the replacement directory for the following reasons: (i) some checks use the replacement files, (ii) some macros bypass broken system headers by installing links to the replacement headers (iii) when used in conjunction with Automake, within each makefile, @var{directory} is used as a relative path from @code{$(top_srcdir)} to each object named in @code{LIBOBJS} and @code{LTLIBOBJS}, etc. @end defmac @sp 1 It is common to merely check for the existence of a function, and ask for its @code{AC_LIBOBJ} replacement if missing. The following macro is a convenient shorthand. @defmac AC_REPLACE_FUNCS (@var{function}@dots{}) @acindex{REPLACE_FUNCS} @ovindex LIBOBJS Like @code{AC_CHECK_FUNCS}, but uses @samp{AC_LIBOBJ(@var{function})} as @var{action-if-not-found}. You can declare your replacement function by enclosing the prototype in @samp{#ifndef HAVE_@var{function}}. If the system has the function, it probably declares it in a header file you should be including, so you shouldn't redeclare it lest your declaration conflict. @end defmac @node Header Files @section Header Files @cindex Header, checking The following macros check for the presence of certain C header files. If there is no macro specifically defined to check for a header file you need, and you don't need to check for any special properties of it, then you can use one of the general header-file check macros. @menu * Header Portability:: Collected knowledge on common headers * Particular Headers:: Special handling to find certain headers * Generic Headers:: How to find other headers @end menu @node Header Portability @subsection Portability of Headers @cindex Portability of headers @cindex Header portability This section tries to collect knowledge about common headers, and the problems they cause. By definition, this list always requires additions. Please help us keeping it as complete as possible. @table @asis @item @file{limits.h} C99 says that @file{limits.h} defines @code{LLONG_MIN}, @code{LLONG_MAX}, and @code{ULLONG_MAX}, but many almost-C99 environments (e.g., default @acronym{GCC} 4.0.2 + glibc 2.4) do not define them. @item @file{inttypes.h} vs.@: @file{stdint.h} @hdrindex{inttypes.h} @hdrindex{stdint.h} The C99 standard says that @file{inttypes.h} includes @file{stdint.h}, so there's no need to include @file{stdint.h} separately in a standard environment. Some implementations have @file{inttypes.h} but not @file{stdint.h} (e.g., Solaris 7), but we don't know of any implementation that has @file{stdint.h} but not @file{inttypes.h}. @item @file{linux/irda.h} @hdrindex{linux/irda.h} It requires @file{linux/types.h} and @file{sys/socket.h}. @item @file{linux/random.h} @hdrindex{linux/random.h} It requires @file{linux/types.h}. @item @file{net/if.h} @hdrindex{net/if.h} On Darwin, this file requires that @file{sys/socket.h} be included beforehand. One should run: @example AC_CHECK_HEADERS([sys/socket.h]) AC_CHECK_HEADERS([net/if.h], [], [], [#include #ifdef STDC_HEADERS # include # include #else # ifdef HAVE_STDLIB_H # include # endif #endif #ifdef HAVE_SYS_SOCKET_H # include #endif ]) @end example @item @file{netinet/if_ether.h} @hdrindex{netinet/if_ether.h} On Darwin, this file requires that @file{stdio.h} and @file{sys/socket.h} be included beforehand. One should run: @example AC_CHECK_HEADERS([sys/socket.h]) AC_CHECK_HEADERS([netinet/if_ether.h], [], [], [#include #ifdef STDC_HEADERS # include # include #else # ifdef HAVE_STDLIB_H # include # endif #endif #ifdef HAVE_SYS_SOCKET_H # include #endif ]) @end example @item @file{stdint.h} See above, item @file{inttypes.h} vs.@: @file{stdint.h}. @item @file{stdlib.h} @hdrindex{stdlib.h} On many systems (e.g., Darwin), @file{stdio.h} is a prerequisite. @item @file{sys/mount.h} @hdrindex{sys/mount.h} On Free@acronym{BSD} 4.8 on ia32 and using gcc version 2.95.4, @file{sys/params.h} is a prerequisite. @item @file{sys/ptem.h} @hdrindex{sys/ptem.h} On Solaris 8, @file{sys/stream.h} is a prerequisite. @item @file{sys/socket.h} @hdrindex{sys/socket.h} On Darwin, @file{stdlib.h} is a prerequisite. @item @file{sys/ucred.h} @hdrindex{sys/ucred.h} On Tru64 5.1, @file{sys/types.h} is a prerequisite. @item @file{X11/extensions/scrnsaver.h} @hdrindex{X11/extensions/scrnsaver.h} Using XFree86, this header requires @file{X11/Xlib.h}, which is probably so required that you might not even consider looking for it. @example AC_CHECK_HEADERS([X11/extensions/scrnsaver.h], [], [], [[#include ]]) @end example @end table @node Particular Headers @subsection Particular Header Checks These macros check for particular system header files---whether they exist, and in some cases whether they declare certain symbols. @defmac AC_HEADER_ASSERT @acindex{HEADER_ASSERT} @cvindex NDEBUG @hdrindex{assert.h} Check whether to enable assertions in the style of @file{assert.h}. Assertions are enabled by default, but the user can override this by invoking @command{configure} with the @option{--disable-assert} option. @end defmac @defmac AC_HEADER_DIRENT @acindex{HEADER_DIRENT} @cvindex HAVE_DIRENT_H @cvindex HAVE_NDIR_H @cvindex HAVE_SYS_DIR_H @cvindex HAVE_SYS_NDIR_H @hdrindex{dirent.h} @hdrindex{sys/ndir.h} @hdrindex{sys/dir.h} @hdrindex{ndir.h} Check for the following header files. For the first one that is found and defines @samp{DIR}, define the listed C preprocessor macro: @multitable {@file{sys/ndir.h}} {@code{HAVE_SYS_NDIR_H}} @item @file{dirent.h} @tab @code{HAVE_DIRENT_H} @item @file{sys/ndir.h} @tab @code{HAVE_SYS_NDIR_H} @item @file{sys/dir.h} @tab @code{HAVE_SYS_DIR_H} @item @file{ndir.h} @tab @code{HAVE_NDIR_H} @end multitable The directory-library declarations in your source code should look something like the following: @example @group #include #ifdef HAVE_DIRENT_H # include # define NAMLEN(dirent) strlen ((dirent)->d_name) #else # define dirent direct # define NAMLEN(dirent) ((dirent)->d_namlen) # ifdef HAVE_SYS_NDIR_H # include # endif # ifdef HAVE_SYS_DIR_H # include # endif # ifdef HAVE_NDIR_H # include # endif #endif @end group @end example Using the above declarations, the program would declare variables to be of type @code{struct dirent}, not @code{struct direct}, and would access the length of a directory entry name by passing a pointer to a @code{struct dirent} to the @code{NAMLEN} macro. This macro also checks for the SCO Xenix @file{dir} and @file{x} libraries. This macro is obsolescent, as all current systems with directory libraries have @code{}. New programs need not use this macro. Also see @code{AC_STRUCT_DIRENT_D_INO} and @code{AC_STRUCT_DIRENT_D_TYPE} (@pxref{Particular Structures}). @end defmac @defmac AC_HEADER_MAJOR @acindex{HEADER_MAJOR} @cvindex MAJOR_IN_MKDEV @cvindex MAJOR_IN_SYSMACROS @hdrindex{sys/mkdev.h} @hdrindex{sys/sysmacros.h} If @file{sys/types.h} does not define @code{major}, @code{minor}, and @code{makedev}, but @file{sys/mkdev.h} does, define @code{MAJOR_IN_MKDEV}; otherwise, if @file{sys/sysmacros.h} does, define @code{MAJOR_IN_SYSMACROS}. @end defmac @defmac AC_HEADER_RESOLV @acindex{HEADER_RESOLV} @cvindex HAVE_RESOLV_H @hdrindex{resolv.h} Checks for header @file{resolv.h}, checking for prerequisites first. To properly use @file{resolv.h}, your code should contain something like the following: @verbatim #ifdef HAVE_SYS_TYPES_H # include #endif #ifdef HAVE_NETINET_IN_H # include /* inet_ functions / structs */ #endif #ifdef HAVE_ARPA_NAMESER_H # include /* DNS HEADER struct */ #endif #ifdef HAVE_NETDB_H # include #endif #include @end verbatim @end defmac @defmac AC_HEADER_STAT @acindex{HEADER_STAT} @cvindex STAT_MACROS_BROKEN @hdrindex{sys/stat.h} If the macros @code{S_ISDIR}, @code{S_ISREG}, etc.@: defined in @file{sys/stat.h} do not work properly (returning false positives), define @code{STAT_MACROS_BROKEN}. This is the case on Tektronix UTekV, Amdahl UTS and Motorola System V/88. This macro is obsolescent, as no current systems have the bug. New programs need not use this macro. @end defmac @defmac AC_HEADER_STDBOOL @acindex{HEADER_STDBOOL} @cvindex HAVE_STDBOOL_H @cvindex HAVE__BOOL @hdrindex{stdbool.h} @hdrindex{system.h} If @file{stdbool.h} exists and conforms to C99, define @code{HAVE_STDBOOL_H} to 1; if the type @code{_Bool} is defined, define @code{HAVE__BOOL} to 1. To fulfill the C99 requirements, your @file{system.h} could contain the following code: @verbatim #ifdef HAVE_STDBOOL_H # include #else # ifndef HAVE__BOOL # ifdef __cplusplus typedef bool _Bool; # else # define _Bool signed char # endif # endif # define bool _Bool # define false 0 # define true 1 # define __bool_true_false_are_defined 1 #endif @end verbatim Alternatively you can use the @samp{stdbool} package of Gnulib (@pxref{Gnulib}); it packages the above code into a replacement header and contains a few other bells and whistles. @end defmac @defmac AC_HEADER_STDC @acindex{HEADER_STDC} @cvindex STDC_HEADERS @hdrindex{stdlib.h} @hdrindex{stdarg.h} @hdrindex{string.h} @hdrindex{float.h} @hdrindex{ctype.h} Define @code{STDC_HEADERS} if the system has C header files conforming to @acronym{ANSI} C89 (@acronym{ISO} C90). Specifically, this macro checks for @file{stdlib.h}, @file{stdarg.h}, @file{string.h}, and @file{float.h}; if the system has those, it probably has the rest of the C89 header files. This macro also checks whether @file{string.h} declares @code{memchr} (and thus presumably the other @code{mem} functions), whether @file{stdlib.h} declare @code{free} (and thus presumably @code{malloc} and other related functions), and whether the @file{ctype.h} macros work on characters with the high bit set, as the C standard requires. If you use this macro, your code can refer to @code{STDC_HEADERS} to determine whether the system has conforming header files (and probably C library functions). This macro is obsolescent, as current systems have conforming header files. New programs need not use this macro. @hdrindex{string.h} @hdrindex{strings.h} Nowadays @file{string.h} is part of the C standard and declares functions like @code{strcpy}, and @file{strings.h} is standardized by Posix and declares @acronym{BSD} functions like @code{bcopy}; but historically, string functions were a major sticking point in this area. If you still want to worry about portability to ancient systems without standard headers, there is so much variation that it is probably easier to declare the functions you use than to figure out exactly what the system header files declare. Some ancient systems contained a mix of functions from the C standard and from @acronym{BSD}; some were mostly standard but lacked @samp{memmove}; some defined the @acronym{BSD} functions as macros in @file{string.h} or @file{strings.h}; some had only the @acronym{BSD} functions but @file{string.h}; some declared the memory functions in @file{memory.h}, some in @file{string.h}; etc. It is probably sufficient to check for one string function and one memory function; if the library had the standard versions of those then it probably had most of the others. If you put the following in @file{configure.ac}: @example # This example is obsolescent. # Nowadays you can omit these macro calls. AC_HEADER_STDC AC_CHECK_FUNCS([strchr memcpy]) @end example @noindent then, in your code, you can use declarations like this: @example @group /* This example is obsolescent. Nowadays you can just #include . */ #ifdef STDC_HEADERS # include #else # ifndef HAVE_STRCHR # define strchr index # define strrchr rindex # endif char *strchr (), *strrchr (); # ifndef HAVE_MEMCPY # define memcpy(d, s, n) bcopy ((s), (d), (n)) # define memmove(d, s, n) bcopy ((s), (d), (n)) # endif #endif @end group @end example @noindent If you use a function like @code{memchr}, @code{memset}, @code{strtok}, or @code{strspn}, which have no @acronym{BSD} equivalent, then macros don't suffice to port to ancient hosts; you must provide an implementation of each function. An easy way to incorporate your implementations only when needed (since the ones in system C libraries may be hand optimized) is to, taking @code{memchr} for example, put it in @file{memchr.c} and use @samp{AC_REPLACE_FUNCS([memchr])}. @end defmac @defmac AC_HEADER_SYS_WAIT @acindex{HEADER_SYS_WAIT} @cvindex HAVE_SYS_WAIT_H @hdrindex{sys/wait.h} If @file{sys/wait.h} exists and is compatible with Posix, define @code{HAVE_SYS_WAIT_H}. Incompatibility can occur if @file{sys/wait.h} does not exist, or if it uses the old @acronym{BSD} @code{union wait} instead of @code{int} to store a status value. If @file{sys/wait.h} is not Posix compatible, then instead of including it, define the Posix macros with their usual interpretations. Here is an example: @example @group #include #ifdef HAVE_SYS_WAIT_H # include #endif #ifndef WEXITSTATUS # define WEXITSTATUS(stat_val) ((unsigned int) (stat_val) >> 8) #endif #ifndef WIFEXITED # define WIFEXITED(stat_val) (((stat_val) & 255) == 0) #endif @end group @end example @noindent This macro is obsolescent, as current systems are compatible with Posix. New programs need not use this macro. @end defmac @cvindex _POSIX_VERSION @hdrindex{unistd.h} @code{_POSIX_VERSION} is defined when @file{unistd.h} is included on Posix systems. If there is no @file{unistd.h}, it is definitely not a Posix system. However, some non-Posix systems do have @file{unistd.h}. The way to check whether the system supports Posix is: @example @group #ifdef HAVE_UNISTD_H # include # include #endif #ifdef _POSIX_VERSION /* Code for Posix systems. */ #endif @end group @end example @defmac AC_HEADER_TIME @acindex{HEADER_TIME} @cvindex TIME_WITH_SYS_TIME @hdrindex{time.h} @hdrindex{sys/time.h} If a program may include both @file{time.h} and @file{sys/time.h}, define @code{TIME_WITH_SYS_TIME}. On some ancient systems, @file{sys/time.h} included @file{time.h}, but @file{time.h} was not protected against multiple inclusion, so programs could not explicitly include both files. This macro is useful in programs that use, for example, @code{struct timeval} as well as @code{struct tm}. It is best used in conjunction with @code{HAVE_SYS_TIME_H}, which can be checked for using @code{AC_CHECK_HEADERS([sys/time.h])}. @example @group #ifdef TIME_WITH_SYS_TIME # include # include #else # ifdef HAVE_SYS_TIME_H # include # else # include # endif #endif @end group @end example @noindent This macro is obsolescent, as current systems can include both files when they exist. New programs need not use this macro. @end defmac @defmac AC_HEADER_TIOCGWINSZ @acindex{HEADER_TIOCGWINSZ} @cvindex GWINSZ_IN_SYS_IOCTL @hdrindex{sys/ioctl.h} @hdrindex{termios.h} @c FIXME: I need clarifications from Jim. If the use of @code{TIOCGWINSZ} requires @file{}, then define @code{GWINSZ_IN_SYS_IOCTL}. Otherwise @code{TIOCGWINSZ} can be found in @file{}. Use: @example @group #ifdef HAVE_TERMIOS_H # include #endif #ifdef GWINSZ_IN_SYS_IOCTL # include #endif @end group @end example @end defmac @node Generic Headers @subsection Generic Header Checks These macros are used to find system header files not covered by the ``particular'' test macros. If you need to check the contents of a header as well as find out whether it is present, you have to write your own test for it (@pxref{Writing Tests}). @defmac AC_CHECK_HEADER (@var{header-file}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_HEADER} If the system header file @var{header-file} is compilable, execute shell commands @var{action-if-found}, otherwise execute @var{action-if-not-found}. If you just want to define a symbol if the header file is available, consider using @code{AC_CHECK_HEADERS} instead. For compatibility issues with older versions of Autoconf, please read below. @end defmac @defmac AC_CHECK_HEADERS (@var{header-file}@dots{}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_HEADERS} @cvindex HAVE_@var{header} For each given system header file @var{header-file} in the blank-separated argument list that exists, define @code{HAVE_@var{header-file}} (in all capitals). If @var{action-if-found} is given, it is additional shell code to execute when one of the header files is found. You can give it a value of @samp{break} to break out of the loop on the first match. If @var{action-if-not-found} is given, it is executed when one of the header files is not found. For compatibility issues with older versions of Autoconf, please read below. @end defmac Previous versions of Autoconf merely checked whether the header was accepted by the preprocessor. This was changed because the old test was inappropriate for typical uses. Headers are typically used to compile, not merely to preprocess, and the old behavior sometimes accepted headers that clashed at compile-time. If you need to check whether a header is preprocessable, you can use @code{AC_PREPROC_IFELSE} (@pxref{Running the Preprocessor}). This scheme, which improves the robustness of the test, also requires that you make sure that headers that must be included before the @var{header-file} be part of the @var{includes}, (@pxref{Default Includes}). If looking for @file{bar.h}, which requires that @file{foo.h} be included before if it exists, we suggest the following scheme: @verbatim AC_CHECK_HEADERS([foo.h]) AC_CHECK_HEADERS([bar.h], [], [], [#ifdef HAVE_FOO_H # include # endif ]) @end verbatim The following variant generates smaller, faster @command{configure} files if you do not need the full power of @code{AC_CHECK_HEADERS}. @defmac AC_CHECK_HEADERS_ONCE (@var{header-file}@dots{}) @acindex{CHECK_HEADERS_ONCE} @cvindex HAVE_@var{header} For each given system header file @var{header-file} in the blank-separated argument list that exists, define @code{HAVE_@var{header-file}} (in all capitals). This is a once-only variant of @code{AC_CHECK_HEADERS}. It generates the checking code at most once, so that @command{configure} is smaller and faster; but the checks cannot be conditionalized and are always done once, early during the @command{configure} run. @end defmac @node Declarations @section Declarations @cindex Declaration, checking The following macros check for the declaration of variables and functions. If there is no macro specifically defined to check for a symbol you need, then you can use the general macros (@pxref{Generic Declarations}) or, for more complex tests, you may use @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}). @menu * Particular Declarations:: Macros to check for certain declarations * Generic Declarations:: How to find other declarations @end menu @node Particular Declarations @subsection Particular Declaration Checks There are no specific macros for declarations. @node Generic Declarations @subsection Generic Declaration Checks These macros are used to find declarations not covered by the ``particular'' test macros. @defmac AC_CHECK_DECL (@var{symbol}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_DECL} If @var{symbol} (a function, variable, or constant) is not declared in @var{includes} and a declaration is needed, run the shell commands @var{action-if-not-found}, otherwise @var{action-if-found}. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). This macro actually tests whether @var{symbol} is defined as a macro or can be used as an r-value, not whether it is really declared, because it is much safer to avoid introducing extra declarations when they are not needed. @end defmac @defmac AC_CHECK_DECLS (@var{symbols}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_DECLS} @cvindex HAVE_DECL_@var{symbol} For each of the @var{symbols} (@emph{comma}-separated list), define @code{HAVE_DECL_@var{symbol}} (in all capitals) to @samp{1} if @var{symbol} is declared, otherwise to @samp{0}. If @var{action-if-not-found} is given, it is additional shell code to execute when one of the function declarations is needed, otherwise @var{action-if-found} is executed. This macro uses an M4 list as first argument: @example AC_CHECK_DECLS([strdup]) AC_CHECK_DECLS([strlen]) AC_CHECK_DECLS([malloc, realloc, calloc, free]) @end example Unlike the other @samp{AC_CHECK_*S} macros, when a @var{symbol} is not declared, @code{HAVE_DECL_@var{symbol}} is defined to @samp{0} instead of leaving @code{HAVE_DECL_@var{symbol}} undeclared. When you are @emph{sure} that the check was performed, use @code{HAVE_DECL_@var{symbol}} in @code{#if}: @example #if !HAVE_DECL_SYMBOL extern char *symbol; #endif @end example @noindent If the test may have not been performed, however, because it is safer @emph{not} to declare a symbol than to use a declaration that conflicts with the system's one, you should use: @example #if defined HAVE_DECL_MALLOC && !HAVE_DECL_MALLOC void *malloc (size_t *s); #endif @end example @noindent You fall into the second category only in extreme situations: either your files may be used without being configured, or they are used during the configuration. In most cases the traditional approach is enough. @end defmac @defmac AC_CHECK_DECLS_ONCE (@var{symbols}) @acindex{CHECK_DECLS_ONCE} @cvindex HAVE_DECL_@var{symbol} For each of the @var{symbols} (@emph{comma}-separated list), define @code{HAVE_DECL_@var{symbol}} (in all capitals) to @samp{1} if @var{symbol} is declared in the default include files, otherwise to @samp{0}. This is a once-only variant of @code{AC_CHECK_DECLS}. It generates the checking code at most once, so that @command{configure} is smaller and faster; but the checks cannot be conditionalized and are always done once, early during the @command{configure} run. @end defmac @node Structures @section Structures @cindex Structure, checking The following macros check for the presence of certain members in C structures. If there is no macro specifically defined to check for a member you need, then you can use the general structure-member macros (@pxref{Generic Structures}) or, for more complex tests, you may use @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}). @menu * Particular Structures:: Macros to check for certain structure members * Generic Structures:: How to find other structure members @end menu @node Particular Structures @subsection Particular Structure Checks The following macros check for certain structures or structure members. @defmac AC_STRUCT_DIRENT_D_INO @acindex{STRUCT_DIRENT_D_INO} @cvindex HAVE_STRUCT_DIRENT_D_INO Perform all the actions of @code{AC_HEADER_DIRENT} (@pxref{Particular Headers}). Then, if @code{struct dirent} contains a @code{d_ino} member, define @code{HAVE_STRUCT_DIRENT_D_INO}. @code{HAVE_STRUCT_DIRENT_D_INO} indicates only the presence of @code{d_ino}, not whether its contents are always reliable. Traditionally, a zero @code{d_ino} indicated a deleted directory entry, though current systems hide this detail from the user and never return zero @code{d_ino} values. Many current systems report an incorrect @code{d_ino} for a directory entry that is a mount point. @end defmac @defmac AC_STRUCT_DIRENT_D_TYPE @acindex{STRUCT_DIRENT_D_TYPE} @cvindex HAVE_STRUCT_DIRENT_D_TYPE Perform all the actions of @code{AC_HEADER_DIRENT} (@pxref{Particular Headers}). Then, if @code{struct dirent} contains a @code{d_type} member, define @code{HAVE_STRUCT_DIRENT_D_TYPE}. @end defmac @defmac AC_STRUCT_ST_BLKSIZE @acindex{STRUCT_ST_BLKSIZE} @cvindex HAVE_STRUCT_STAT_ST_BLKSIZE @cvindex HAVE_ST_BLKSIZE If @code{struct stat} contains an @code{st_blksize} member, define @code{HAVE_STRUCT_STAT_ST_BLKSIZE}. The former name, @code{HAVE_ST_BLKSIZE} is to be avoided, as its support will cease in the future. This macro is obsoleted, and should be replaced by @example AC_CHECK_MEMBERS([struct stat.st_blksize]) @end example @end defmac @defmac AC_STRUCT_ST_BLOCKS @acindex{STRUCT_ST_BLOCKS} @cvindex HAVE_STRUCT_STAT_ST_BLOCKS @cvindex HAVE_ST_BLOCKS @ovindex LIBOBJS If @code{struct stat} contains an @code{st_blocks} member, define @code{HAVE_STRUCT_STAT_ST_BLOCKS}. Otherwise, require an @code{AC_LIBOBJ} replacement of @samp{fileblocks}. The former name, @code{HAVE_ST_BLOCKS} is to be avoided, as its support will cease in the future. @end defmac @defmac AC_STRUCT_ST_RDEV @acindex{STRUCT_ST_RDEV} @cvindex HAVE_ST_RDEV @cvindex HAVE_STRUCT_STAT_ST_RDEV If @code{struct stat} contains an @code{st_rdev} member, define @code{HAVE_STRUCT_STAT_ST_RDEV}. The former name for this macro, @code{HAVE_ST_RDEV}, is to be avoided as it will cease to be supported in the future. Actually, even the new macro is obsolete and should be replaced by: @example AC_CHECK_MEMBERS([struct stat.st_rdev]) @end example @end defmac @defmac AC_STRUCT_TM @acindex{STRUCT_TM} @cvindex TM_IN_SYS_TIME @hdrindex{time.h} @hdrindex{sys/time.h} If @file{time.h} does not define @code{struct tm}, define @code{TM_IN_SYS_TIME}, which means that including @file{sys/time.h} had better define @code{struct tm}. This macro is obsolescent, as @file{time.h} defines @code{struct tm} in current systems. New programs need not use this macro. @end defmac @defmac AC_STRUCT_TIMEZONE @acindex{STRUCT_TIMEZONE} @cvindex HAVE_TM_ZONE @cvindex HAVE_TZNAME Figure out how to get the current timezone. If @code{struct tm} has a @code{tm_zone} member, define @code{HAVE_STRUCT_TM_TM_ZONE} (and the obsoleted @code{HAVE_TM_ZONE}). Otherwise, if the external array @code{tzname} is found, define @code{HAVE_TZNAME}; if it is declared, define @code{HAVE_DECL_TZNAME}. @end defmac @node Generic Structures @subsection Generic Structure Checks These macros are used to find structure members not covered by the ``particular'' test macros. @defmac AC_CHECK_MEMBER (@var{aggregate}.@var{member}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_MEMBER} Check whether @var{member} is a member of the aggregate @var{aggregate}. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). @example AC_CHECK_MEMBER([struct passwd.pw_gecos], [], [AC_MSG_ERROR([We need `passwd.pw_gecos'!])], [#include ]) @end example You can use this macro for submembers: @example AC_CHECK_MEMBER(struct top.middle.bot) @end example @end defmac @defmac AC_CHECK_MEMBERS (@var{members}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_MEMBERS} Check for the existence of each @samp{@var{aggregate}.@var{member}} of @var{members} using the previous macro. When @var{member} belongs to @var{aggregate}, define @code{HAVE_@var{aggregate}_@var{member}} (in all capitals, with spaces and dots replaced by underscores). If @var{action-if-found} is given, it is executed for each of the found members. If @var{action-if-not-found} is given, it is executed for each of the members that could not be found. This macro uses M4 lists: @example AC_CHECK_MEMBERS([struct stat.st_rdev, struct stat.st_blksize]) @end example @end defmac @node Types @section Types @cindex Types @cindex C types The following macros check for C types, either builtin or typedefs. If there is no macro specifically defined to check for a type you need, and you don't need to check for any special properties of it, then you can use a general type-check macro. @menu * Particular Types:: Special handling to find certain types * Generic Types:: How to find other types @end menu @node Particular Types @subsection Particular Type Checks @hdrindex{sys/types.h} @hdrindex{stdlib.h} @hdrindex{stdint.h} @hdrindex{inttypes.h} These macros check for particular C types in @file{sys/types.h}, @file{stdlib.h}, @file{stdint.h}, @file{inttypes.h} and others, if they exist. The Gnulib @code{stdint} module is an alternate way to define many of these symbols; it is useful if you prefer your code to assume a C99-or-better environment. @xref{Gnulib}. @defmac AC_TYPE_GETGROUPS @acindex{TYPE_GETGROUPS} @cvindex GETGROUPS_T Define @code{GETGROUPS_T} to be whichever of @code{gid_t} or @code{int} is the base type of the array argument to @code{getgroups}. @end defmac @defmac AC_TYPE_INT8_T @acindex{TYPE_INT8_T} @cvindex HAVE_INT8_T @cvindex int8_t If @file{stdint.h} or @file{inttypes.h} defines the type @code{int8_t}, define @code{HAVE_INT8_T}. Otherwise, define @code{int8_t} to a signed integer type that is exactly 8 bits wide and that uses two's complement representation, if such a type exists. @end defmac @defmac AC_TYPE_INT16_T @acindex{TYPE_INT16_T} @cvindex HAVE_INT16_T @cvindex int16_t This is like @code{AC_TYPE_INT8_T}, except for 16-bit integers. @end defmac @defmac AC_TYPE_INT32_T @acindex{TYPE_INT32_T} @cvindex HAVE_INT32_T @cvindex int32_t This is like @code{AC_TYPE_INT8_T}, except for 32-bit integers. @end defmac @defmac AC_TYPE_INT64_T @acindex{TYPE_INT64_T} @cvindex HAVE_INT64_T @cvindex int64_t This is like @code{AC_TYPE_INT8_T}, except for 64-bit integers. @end defmac @defmac AC_TYPE_INTMAX_T @acindex{TYPE_INTMAX_T} @cvindex HAVE_INTMAX_T @cvindex intmax_t If @file{stdint.h} or @file{inttypes.h} defines the type @code{intmax_t}, define @code{HAVE_INTMAX_T}. Otherwise, define @code{intmax_t} to the widest signed integer type. @end defmac @defmac AC_TYPE_INTPTR_T @acindex{TYPE_INTPTR_T} @cvindex HAVE_INTPTR_T @cvindex intptr_t If @file{stdint.h} or @file{inttypes.h} defines the type @code{intptr_t}, define @code{HAVE_INTPTR_T}. Otherwise, define @code{intptr_t} to a signed integer type wide enough to hold a pointer, if such a type exists. @end defmac @defmac AC_TYPE_LONG_DOUBLE @acindex{TYPE_LONG_DOUBLE} @cvindex HAVE_LONG_DOUBLE If the C compiler supports a working @code{long double} type, define @code{HAVE_LONG_DOUBLE}. The @code{long double} type might have the same range and precision as @code{double}. @end defmac @defmac AC_TYPE_LONG_DOUBLE_WIDER @acindex{TYPE_LONG_DOUBLE_WIDER} @cvindex HAVE_LONG_DOUBLE_WIDER If the C compiler supports a working @code{long double} type with more range or precision than the @code{double} type, define @code{HAVE_LONG_DOUBLE_WIDER}. @end defmac @defmac AC_TYPE_LONG_LONG_INT @acindex{TYPE_LONG_LONG_INT} @cvindex HAVE_LONG_LONG_INT If the C compiler supports a working @code{long long int} type, define @code{HAVE_LONG_LONG_INT}. @end defmac @defmac AC_TYPE_MBSTATE_T @acindex{TYPE_MBSTATE_T} @cvindex mbstate_t @hdrindex{wchar.h} Define @code{HAVE_MBSTATE_T} if @code{} declares the @code{mbstate_t} type. Also, define @code{mbstate_t} to be a type if @code{} does not declare it. @end defmac @defmac AC_TYPE_MODE_T @acindex{TYPE_MODE_T} @cvindex mode_t Define @code{mode_t} to a suitable type, if standard headers do not define it. @end defmac @defmac AC_TYPE_OFF_T @acindex{TYPE_OFF_T} @cvindex off_t Define @code{off_t} to a suitable type, if standard headers do not define it. @end defmac @defmac AC_TYPE_PID_T @acindex{TYPE_PID_T} @cvindex pid_t Define @code{pid_t} to a suitable type, if standard headers do not define it. @end defmac @defmac AC_TYPE_SIGNAL @acindex{TYPE_SIGNAL} @cvindex RETSIGTYPE @hdrindex{signal.h} If @file{signal.h} declares @code{signal} as returning a pointer to a function returning @code{void}, define @code{RETSIGTYPE} to be @code{void}; otherwise, define it to be @code{int}. Define signal handlers as returning type @code{RETSIGTYPE}: @example @group RETSIGTYPE hup_handler () @{ @dots{} @} @end group @end example @end defmac @defmac AC_TYPE_SIZE_T @acindex{TYPE_SIZE_T} @cvindex size_t Define @code{size_t} to a suitable type, if standard headers do not define it. @end defmac @defmac AC_TYPE_SSIZE_T @acindex{TYPE_SSIZE_T} @cvindex ssize_t Define @code{ssize_t} to a suitable type, if standard headers do not define it. @end defmac @defmac AC_TYPE_UID_T @acindex{TYPE_UID_T} @cvindex uid_t @cvindex gid_t Define @code{uid_t} and @code{gid_t} to suitable types, if standard headers do not define them. @end defmac @defmac AC_TYPE_UINT8_T @acindex{TYPE_UINT8_T} @cvindex HAVE_UINT8_T @cvindex uint8_t If @file{stdint.h} or @file{inttypes.h} defines the type @code{uint8_t}, define @code{HAVE_UINT8_T}. Otherwise, define @code{uint8_t} to an unsigned integer type that is exactly 8 bits wide, if such a type exists. @end defmac @defmac AC_TYPE_UINT16_T @acindex{TYPE_UINT16_T} @cvindex HAVE_UINT16_T @cvindex uint16_t This is like @code{AC_TYPE_UINT8_T}, except for 16-bit unsigned integers. @end defmac @defmac AC_TYPE_UINT32_T @acindex{TYPE_UINT32_T} @cvindex HAVE_UINT32_T @cvindex uint32_t This is like @code{AC_TYPE_UINT8_T}, except for 32-bit unsigned integers. @end defmac @defmac AC_TYPE_UINT64_T @acindex{TYPE_UINT64_T} @cvindex HAVE_UINT64_T @cvindex uint64_t This is like @code{AC_TYPE_UINT8_T}, except for 64-bit unsigned integers. @end defmac @defmac AC_TYPE_UINTMAX_T @acindex{TYPE_UINTMAX_T} @cvindex HAVE_UINTMAX_T @cvindex uintmax_t If @file{stdint.h} or @file{inttypes.h} defines the type @code{uintmax_t}, define @code{HAVE_UINTMAX_T}. Otherwise, define @code{uintmax_t} to the widest unsigned integer type. @end defmac @defmac AC_TYPE_UINTPTR_T @acindex{TYPE_UINTPTR_T} @cvindex HAVE_UINTPTR_T @cvindex uintptr_t If @file{stdint.h} or @file{inttypes.h} defines the type @code{uintptr_t}, define @code{HAVE_UINTPTR_T}. Otherwise, define @code{uintptr_t} to an unsigned integer type wide enough to hold a pointer, if such a type exists. @end defmac @defmac AC_TYPE_UNSIGNED_LONG_LONG_INT @acindex{TYPE_UNSIGNED_LONG_LONG_INT} @cvindex HAVE_UNSIGNED_LONG_LONG_INT If the C compiler supports a working @code{unsigned long long int} type, define @code{HAVE_UNSIGNED_LONG_LONG_INT}. @end defmac @node Generic Types @subsection Generic Type Checks These macros are used to check for types not covered by the ``particular'' test macros. @defmac AC_CHECK_TYPE (@var{type}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_TYPE} Check whether @var{type} is defined. It may be a compiler builtin type or defined by the @var{includes} (@pxref{Default Includes}). @end defmac @defmac AC_CHECK_TYPES (@var{types}, @ovar{action-if-found}, @ovar{action-if-not-found}, @dvar{includes, default-includes}) @acindex{CHECK_TYPES} For each @var{type} of the @var{types} that is defined, define @code{HAVE_@var{type}} (in all capitals). If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). If @var{action-if-found} is given, it is additional shell code to execute when one of the types is found. If @var{action-if-not-found} is given, it is executed when one of the types is not found. This macro uses M4 lists: @example AC_CHECK_TYPES([ptrdiff_t]) AC_CHECK_TYPES([unsigned long long int, uintmax_t]) @end example @end defmac Autoconf, up to 2.13, used to provide to another version of @code{AC_CHECK_TYPE}, broken by design. In order to keep backward compatibility, a simple heuristics, quite safe but not totally, is implemented. In case of doubt, read the documentation of the former @code{AC_CHECK_TYPE}, see @ref{Obsolete Macros}. @node Compilers and Preprocessors @section Compilers and Preprocessors @cindex Compilers @cindex Preprocessors @ovindex EXEEXT All the tests for compilers (@code{AC_PROG_CC}, @code{AC_PROG_CXX}, @code{AC_PROG_F77}) define the output variable @code{EXEEXT} based on the output of the compiler, typically to the empty string if Posix and @samp{.exe} if a @acronym{DOS} variant. @ovindex OBJEXT They also define the output variable @code{OBJEXT} based on the output of the compiler, after @file{.c} files have been excluded, typically to @samp{o} if Posix, @samp{obj} if a @acronym{DOS} variant. If the compiler being used does not produce executables, the tests fail. If the executables can't be run, and cross-compilation is not enabled, they fail too. @xref{Manual Configuration}, for more on support for cross compiling. @menu * Specific Compiler Characteristics:: Some portability issues * Generic Compiler Characteristics:: Language independent tests and features * C Compiler:: Checking its characteristics * C++ Compiler:: Likewise * Objective C Compiler:: Likewise * Erlang Compiler and Interpreter:: Likewise * Fortran Compiler:: Likewise @end menu @node Specific Compiler Characteristics @subsection Specific Compiler Characteristics Some compilers exhibit different behaviors. @table @asis @item Static/Dynamic Expressions Autoconf relies on a trick to extract one bit of information from the C compiler: using negative array sizes. For instance the following excerpt of a C source demonstrates how to test whether @samp{int} objects are 4 bytes wide: @example static int test_array[sizeof (int) == 4 ? 1 : -1]; @end example @noindent To our knowledge, there is a single compiler that does not support this trick: the @acronym{HP} C compilers (the real ones, not only the ``bundled'') on @acronym{HP-UX} 11.00. They incorrectly reject the above program with the diagnostic ``Variable-length arrays cannot have static storage.'' This bug comes from @acronym{HP} compilers' mishandling of @code{sizeof (int)}, not from the @code{? 1 : -1}, and Autoconf works around this problem by casting @code{sizeof (int)} to @code{long int} before comparing it. @end table @node Generic Compiler Characteristics @subsection Generic Compiler Characteristics @defmac AC_CHECK_SIZEOF (@var{type}, @ovar{unused}, @dvar{includes, default-includes}) @acindex{CHECK_SIZEOF} Define @code{SIZEOF_@var{type}} (@pxref{Standard Symbols}) to be the size in bytes of @var{type}. If @samp{type} is unknown, it gets a size of 0. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). This macro now works even when cross-compiling. The @var{unused} argument was used when cross-compiling. For example, the call @example AC_CHECK_SIZEOF([int *]) @end example @noindent defines @code{SIZEOF_INT_P} to be 8 on DEC Alpha AXP systems. @end defmac @defmac AC_CHECK_ALIGNOF (@var{type}, @dvar{includes, default-includes}) @acindex{CHECK_ALIGNOF} Define @code{ALIGNOF_@var{type}} (@pxref{Standard Symbols}) to be the alignment in bytes of @var{type}. If @samp{type} is unknown, it gets a size of 0. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). @end defmac @defmac AC_COMPUTE_INT (@var{var}, @var{expression}, @dvar{includes, default-includes}, @ovar{action-if-fails}) @acindex{COMPUTE_INT} Store into the shell variable @var{var} the value of the integer @var{expression}. The value should fit in an initializer in a C variable of type @code{signed long}. To support cross compilation (in which case, the macro only works on hosts that use twos-complement arithmetic), it should be possible to evaluate the expression at compile-time. If no @var{includes} are specified, the default includes are used (@pxref{Default Includes}). Execute @var{action-if-fails} if the value cannot be determined correctly. @end defmac @defmac AC_LANG_WERROR @acindex{LANG_WERROR} Normally Autoconf ignores warnings generated by the compiler, linker, and preprocessor. If this macro is used, warnings count as fatal errors for the current language. This macro is useful when the results of configuration are used where warnings are unacceptable; for instance, if parts of a program are built with the @acronym{GCC} @option{-Werror} option. If the whole program is built using @option{-Werror} it is often simpler to put @option{-Werror} in the compiler flags (@code{CFLAGS}, etc.). @end defmac @node C Compiler @subsection C Compiler Characteristics The following macros provide ways to find and exercise a C Compiler. There are a few constructs that ought to be avoided, but do not deserve being checked for, since they can easily be worked around. @table @asis @item Don't use lines containing solitary backslashes They tickle a bug in the @acronym{HP-UX} C compiler (checked on @acronym{HP-UX} 10.20, 11.00, and 11i). When given the following source: @example #ifdef __STDC__ /\ * A comment with backslash-newlines in it. %@{ %@} *\ \ / char str[] = "\\ " A string with backslash-newlines in it %@{ %@} \\ ""; char apostrophe = '\\ \ '\ '; #endif @end example @noindent the compiler incorrectly fails with the diagnostics ``Non-terminating comment at end of file'' and ``Missing @samp{#endif} at end of file.'' Removing the lines with solitary backslashes solves the problem. @item Don't compile several files at once if output matters to you Some compilers, such as @acronym{HP}'s, report names of files being compiled when given more than one file operand. For instance: @example $ @kbd{cc a.c b.c} a.c: b.c: @end example @noindent This can cause problems if you observe the output of the compiler to detect failures. Invoking @samp{cc -c a.c && cc -c b.c && cc -o c a.o b.o} solves the issue. @item Don't rely on @code{#error} failing The @sc{irix} C compiler does not fail when #error is preprocessed; it simply emits a diagnostic and continues, exiting successfully. So, instead of an error directive like @code{#error "Unsupported word size"} it is more portable to use an invalid directive like @code{#Unsupported word size} in Autoconf tests. In ordinary source code, @code{#error} is OK, since installers with inadequate compilers like @sc{irix} can simply examine these compilers' diagnostic output. @item Don't rely on correct @code{#line} support On Solaris, @command{c89} (at least Sun C 5.3 through 5.8) diagnoses @code{#line} directives whose line numbers are greater than 32767. Nothing in Posix makes this invalid. That is why Autoconf stopped issuing @code{#line} directives. @end table @defmac AC_PROG_CC (@ovar{compiler-search-list}) @acindex{PROG_CC} @ovindex CC @ovindex CFLAGS Determine a C compiler to use. If @code{CC} is not already set in the environment, check for @code{gcc} and @code{cc}, then for other C compilers. Set output variable @code{CC} to the name of the compiler found. This macro may, however, be invoked with an optional first argument which, if specified, must be a blank-separated list of C compilers to search for. This just gives the user an opportunity to specify an alternative search list for the C compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_CC} like this: @example AC_PROG_CC([gcc cl cc]) @end example If the C compiler does not handle function prototypes correctly by default, try to add an option to output variable @code{CC} to make it so. This macro tries various options that select standard-conformance modes on various systems. After calling this macro you can check whether the C compiler has been set to accept @acronym{ANSI} C89 (@acronym{ISO} C90); if not, the shell variable @code{ac_cv_prog_cc_c89} is set to @samp{no}. See also @code{AC_C_PROTOTYPES} below. If using the @acronym{GNU} C compiler, set shell variable @code{GCC} to @samp{yes}. If output variable @code{CFLAGS} was not already set, set it to @option{-g -O2} for the @acronym{GNU} C compiler (@option{-O2} on systems where @acronym{GCC} does not accept @option{-g}), or @option{-g} for other compilers. @end defmac @defmac AC_PROG_CC_C_O @acindex{PROG_CC_C_O} @cvindex NO_MINUS_C_MINUS_O If the C compiler does not accept the @option{-c} and @option{-o} options simultaneously, define @code{NO_MINUS_C_MINUS_O}. This macro actually tests both the compiler found by @code{AC_PROG_CC}, and, if different, the first @code{cc} in the path. The test fails if one fails. This macro was created for @acronym{GNU} Make to choose the default C compilation rule. @end defmac @defmac AC_PROG_CPP @acindex{PROG_CPP} @ovindex CPP Set output variable @code{CPP} to a command that runs the C preprocessor. If @samp{$CC -E} doesn't work, @file{/lib/cpp} is used. It is only portable to run @code{CPP} on files with a @file{.c} extension. Some preprocessors don't indicate missing include files by the error status. For such preprocessors an internal variable is set that causes other macros to check the standard error from the preprocessor and consider the test failed if any warnings have been reported. For most preprocessors, though, warnings do not cause include-file tests to fail unless @code{AC_PROG_CPP_WERROR} is also specified. @end defmac @defmac AC_PROG_CPP_WERROR @acindex{PROG_CPP_WERROR} @ovindex CPP This acts like @code{AC_PROG_CPP}, except it treats warnings from the preprocessor as errors even if the preprocessor exit status indicates success. This is useful for avoiding headers that generate mandatory warnings, such as deprecation notices. @end defmac The following macros check for C compiler or machine architecture features. To check for characteristics not listed here, use @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}) or @code{AC_RUN_IFELSE} (@pxref{Runtime}). @defmac AC_PROG_CC_STDC @acindex{PROG_CC_STDC} If the C compiler cannot compile @acronym{ISO} Standard C (currently C99), try to add an option to output variable @code{CC} to make it work. If the compiler does not support C99, fall back to supporting @acronym{ANSI} C89 (@acronym{ISO} C90). After calling this macro you can check whether the C compiler has been set to accept Standard C; if not, the shell variable @code{ac_cv_prog_cc_stdc} is set to @samp{no}. @end defmac @defmac AC_PROG_CC_C89 @acindex{PROG_CC_C89} If the C compiler is not in @acronym{ANSI} C89 (@acronym{ISO} C90) mode by default, try to add an option to output variable @code{CC} to make it so. This macro tries various options that select @acronym{ANSI} C89 on some system or another. It considers the compiler to be in @acronym{ANSI} C89 mode if it handles function prototypes correctly. After calling this macro you can check whether the C compiler has been set to accept @acronym{ANSI} C89; if not, the shell variable @code{ac_cv_prog_cc_c89} is set to @samp{no}. This macro is called automatically by @code{AC_PROG_CC}. @end defmac @defmac AC_PROG_CC_C99 @acindex{PROG_CC_C99} If the C compiler is not in C99 mode by default, try to add an option to output variable @code{CC} to make it so. This macro tries various options that select C99 on some system or another. It considers the compiler to be in C99 mode if it handles @code{_Bool}, @code{//} comments, flexible array members, @code{inline}, @code{long long int}, mixed code and declarations, named initialization of structs, @code{restrict}, @code{va_copy}, varargs macros, variable declarations in @code{for} loops, and variable length arrays. After calling this macro you can check whether the C compiler has been set to accept C99; if not, the shell variable @code{ac_cv_prog_cc_c99} is set to @samp{no}. @end defmac @defmac AC_C_BACKSLASH_A @acindex{HAVE_C_BACKSLASH_A} Define @samp{HAVE_C_BACKSLASH_A} to 1 if the C compiler understands @samp{\a}. This macro is obsolescent, as current C compilers understand @samp{\a}. New programs need not use this macro. @end defmac @defmac AC_C_BIGENDIAN (@ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-unknown}) @acindex{C_BIGENDIAN} @cvindex WORDS_BIGENDIAN @cindex Endianness If words are stored with the most significant byte first (like Motorola and SPARC CPUs), execute @var{action-if-true}. If words are stored with the least significant byte first (like Intel and VAX CPUs), execute @var{action-if-false}. This macro runs a test-case if endianness cannot be determined from the system header files. When cross-compiling, the test-case is not run but grep'ed for some magic values. @var{action-if-unknown} is executed if the latter case fails to determine the byte sex of the host system. The default for @var{action-if-true} is to define @samp{WORDS_BIGENDIAN}. The default for @var{action-if-false} is to do nothing. And finally, the default for @var{action-if-unknown} is to abort configure and tell the installer which variable he should preset to bypass this test. @end defmac @defmac AC_C_CONST @acindex{C_CONST} @cvindex const If the C compiler does not fully support the @code{const} keyword, define @code{const} to be empty. Some C compilers that do not define @code{__STDC__} do support @code{const}; some compilers that define @code{__STDC__} do not completely support @code{const}. Programs can simply use @code{const} as if every C compiler supported it; for those that don't, the makefile or configuration header file defines it as empty. Occasionally installers use a C++ compiler to compile C code, typically because they lack a C compiler. This causes problems with @code{const}, because C and C++ treat @code{const} differently. For example: @example const int foo; @end example @noindent is valid in C but not in C++. These differences unfortunately cannot be papered over by defining @code{const} to be empty. If @command{autoconf} detects this situation, it leaves @code{const} alone, as this generally yields better results in practice. However, using a C++ compiler to compile C code is not recommended or supported, and installers who run into trouble in this area should get a C compiler like @acronym{GCC} to compile their C code. This macro is obsolescent, as current C compilers support @code{const}. New programs need not use this macro. @end defmac @defmac AC_C_RESTRICT @acindex{C_RESTRICT} @cvindex restrict If the C compiler recognizes the @code{restrict} keyword, don't do anything. If it recognizes only a variant spelling (@code{__restrict}, @code{__restrict__}, or @code{_Restrict}), then define @code{restrict} to that. Otherwise, define @code{restrict} to be empty. Thus, programs may simply use @code{restrict} as if every C compiler supported it; for those that do not, the makefile or configuration header defines it away. Although support in C++ for the @code{restrict} keyword is not required, several C++ compilers do accept the keyword. This macro works for them, too. @end defmac @defmac AC_C_VOLATILE @acindex{C_VOLATILE} @cvindex volatile If the C compiler does not understand the keyword @code{volatile}, define @code{volatile} to be empty. Programs can simply use @code{volatile} as if every C compiler supported it; for those that do not, the makefile or configuration header defines it as empty. If the correctness of your program depends on the semantics of @code{volatile}, simply defining it to be empty does, in a sense, break your code. However, given that the compiler does not support @code{volatile}, you are at its mercy anyway. At least your program compiles, when it wouldn't before. @xref{Volatile Objects}, for more about @code{volatile}. In general, the @code{volatile} keyword is a standard C feature, so you might expect that @code{volatile} is available only when @code{__STDC__} is defined. However, Ultrix 4.3's native compiler does support volatile, but does not define @code{__STDC__}. This macro is obsolescent, as current C compilers support @code{volatile}. New programs need not use this macro. @end defmac @defmac AC_C_INLINE @acindex{C_INLINE} @cvindex inline If the C compiler supports the keyword @code{inline}, do nothing. Otherwise define @code{inline} to @code{__inline__} or @code{__inline} if it accepts one of those, otherwise define @code{inline} to be empty. @end defmac @defmac AC_C_CHAR_UNSIGNED @acindex{C_CHAR_UNSIGNED} @cvindex __CHAR_UNSIGNED__ If the C type @code{char} is unsigned, define @code{__CHAR_UNSIGNED__}, unless the C compiler predefines it. @end defmac @defmac AC_C_STRINGIZE @acindex{C_STRINGIZE} @cvindex HAVE_STRINGIZE If the C preprocessor supports the stringizing operator, define @code{HAVE_STRINGIZE}. The stringizing operator is @samp{#} and is found in macros such as this: @example #define x(y) #y @end example This macro is obsolescent, as current C compilers support the stringizing operator. New programs need not use this macro. @end defmac @defmac AC_C_FLEXIBLE_ARRAY_MEMBER @acindex{C_FLEXIBLE_ARRAY_MEMBER} @cvindex FLEXIBLE_ARRAY_MEMBER If the C compiler supports flexible array members, define @code{FLEXIBLE_ARRAY_MEMBER} to nothing; otherwise define it to 1. That way, a declaration like this: @example struct s @{ size_t n_vals; double val[FLEXIBLE_ARRAY_MEMBER]; @}; @end example @noindent will let applications use the ``struct hack'' even with compilers that do not support flexible array members. To allocate and use such an object, you can use code like this: @example size_t i; size_t n = compute_value_count (); struct s *p = malloc (offsetof (struct s, val) + n * sizeof (double)); p->n_vals = n; for (i = 0; i < n; i++) p->val[i] = compute_value (i); @end example @end defmac @defmac AC_C_VARARRAYS @acindex{C_VARARRAYS} @cvindex HAVE_C_VARARRAYS If the C compiler supports variable-length arrays, define @code{HAVE_C_VARRAYS}. A variable-length array is an array of automatic storage duration whose length is determined at run time, when the array is declared. @end defmac @defmac AC_C_TYPEOF @acindex{C_TYPEOF} @cvindex HAVE_TYPEOF @cvindex typeof If the C compiler supports @acronym{GCC}'s @code{typeof} syntax either directly or through a different spelling of the keyword (e.g., @code{__typeof__}), define @code{HAVE_TYPEOF}. If the support is available only through a different spelling, define @code{typeof} to that spelling. @end defmac @defmac AC_C_PROTOTYPES @acindex{C_PROTOTYPES} @cvindex PROTOTYPES @cvindex __PROTOTYPES @cvindex PARAMS If function prototypes are understood by the compiler (as determined by @code{AC_PROG_CC}), define @code{PROTOTYPES} and @code{__PROTOTYPES}. Defining @code{__PROTOTYPES} is for the benefit of header files that cannot use macros that infringe on user name space. This macro is obsolescent, as current C compilers support prototypes. New programs need not use this macro. @end defmac @defmac AC_PROG_GCC_TRADITIONAL @acindex{PROG_GCC_TRADITIONAL} @ovindex CC Add @option{-traditional} to output variable @code{CC} if using the @acronym{GNU} C compiler and @code{ioctl} does not work properly without @option{-traditional}. That usually happens when the fixed header files have not been installed on an old system. This macro is obsolescent, since current versions of the @acronym{GNU} C compiler fix the header files automatically when installed. @end defmac @node C++ Compiler @subsection C++ Compiler Characteristics @defmac AC_PROG_CXX (@ovar{compiler-search-list}) @acindex{PROG_CXX} @ovindex CXX @ovindex CXXFLAGS Determine a C++ compiler to use. Check whether the environment variable @code{CXX} or @code{CCC} (in that order) is set; if so, then set output variable @code{CXX} to its value. Otherwise, if the macro is invoked without an argument, then search for a C++ compiler under the likely names (first @code{g++} and @code{c++} then other names). If none of those checks succeed, then as a last resort set @code{CXX} to @code{g++}. This macro may, however, be invoked with an optional first argument which, if specified, must be a blank-separated list of C++ compilers to search for. This just gives the user an opportunity to specify an alternative search list for the C++ compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_CXX} like this: @example AC_PROG_CXX([gcc cl KCC CC cxx cc++ xlC aCC c++ g++]) @end example If using the @acronym{GNU} C++ compiler, set shell variable @code{GXX} to @samp{yes}. If output variable @code{CXXFLAGS} was not already set, set it to @option{-g -O2} for the @acronym{GNU} C++ compiler (@option{-O2} on systems where G++ does not accept @option{-g}), or @option{-g} for other compilers. @end defmac @defmac AC_PROG_CXXCPP @acindex{PROG_CXXCPP} @ovindex CXXCPP Set output variable @code{CXXCPP} to a command that runs the C++ preprocessor. If @samp{$CXX -E} doesn't work, @file{/lib/cpp} is used. It is portable to run @code{CXXCPP} only on files with a @file{.c}, @file{.C}, @file{.cc}, or @file{.cpp} extension. Some preprocessors don't indicate missing include files by the error status. For such preprocessors an internal variable is set that causes other macros to check the standard error from the preprocessor and consider the test failed if any warnings have been reported. However, it is not known whether such broken preprocessors exist for C++. @end defmac @defmac AC_PROG_CXX_C_O @acindex{PROG_CXX_C_O} @cvindex CXX_NO_MINUS_C_MINUS_O Test whether the C++ compiler accepts the options @option{-c} and @option{-o} simultaneously, and define @code{CXX_NO_MINUS_C_MINUS_O}, if it does not. @end defmac @node Objective C Compiler @subsection Objective C Compiler Characteristics @defmac AC_PROG_OBJC (@ovar{compiler-search-list}) @acindex{PROG_OBJC} @ovindex OBJC @ovindex OBJCFLAGS Determine an Objective C compiler to use. If @code{OBJC} is not already set in the environment, check for Objective C compilers. Set output variable @code{OBJC} to the name of the compiler found. This macro may, however, be invoked with an optional first argument which, if specified, must be a blank-separated list of Objective C compilers to search for. This just gives the user an opportunity to specify an alternative search list for the Objective C compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_OBJC} like this: @example AC_PROG_OBJC([gcc objcc objc]) @end example If using the @acronym{GNU} Objective C compiler, set shell variable @code{GOBJC} to @samp{yes}. If output variable @code{OBJCFLAGS} was not already set, set it to @option{-g -O2} for the @acronym{GNU} Objective C compiler (@option{-O2} on systems where @command{gcc} does not accept @option{-g}), or @option{-g} for other compilers. @end defmac @defmac AC_PROG_OBJCCPP @acindex{PROG_OBJCCPP} @ovindex OBJCCPP Set output variable @code{OBJCCPP} to a command that runs the Objective C preprocessor. If @samp{$OBJC -E} doesn't work, @file{/lib/cpp} is used. @end defmac @node Erlang Compiler and Interpreter @subsection Erlang Compiler and Interpreter Characteristics @cindex Erlang Autoconf defines the following macros for determining paths to the essential Erlang/OTP programs: @defmac AC_ERLANG_PATH_ERLC (@ovar{value-if-not-found}, @ovar{path}) @acindex{ERLANG_PATH_ERLC} @ovindex ERLC @ovindex ERLCFLAGS Determine an Erlang compiler to use. If @code{ERLC} is not already set in the environment, check for @command{erlc}. Set output variable @code{ERLC} to the complete path of the compiler command found. In addition, if @code{ERLCFLAGS} is not set in the environment, set it to an empty value. The two optional arguments have the same meaning as the two last arguments of macro @code{AC_PROG_PATH} for looking for the @command{erlc} program. For example, to look for @command{erlc} only in the @file{/usr/lib/erlang/bin} directory: @example AC_ERLANG_PATH_ERLC([not found], [/usr/lib/erlang/bin]) @end example @end defmac @defmac AC_ERLANG_NEED_ERLC (@ovar{path}) @acindex{ERLANG_NEED_ERLC} A simplified variant of the @code{AC_ERLANG_PATH_ERLC} macro, that prints an error message and exits the @command{configure} script if the @command{erlc} program is not found. @end defmac @defmac AC_ERLANG_PATH_ERL (@ovar{value-if-not-found}, @ovar{path}) @acindex{ERLANG_PATH_ERL} @ovindex ERL Determine an Erlang interpreter to use. If @code{ERL} is not already set in the environment, check for @command{erl}. Set output variable @code{ERL} to the complete path of the interpreter command found. The two optional arguments have the same meaning as the two last arguments of macro @code{AC_PROG_PATH} for looking for the @command{erl} program. For example, to look for @command{erl} only in the @file{/usr/lib/erlang/bin} directory: @example AC_ERLANG_PATH_ERL([not found], [/usr/lib/erlang/bin]) @end example @end defmac @defmac AC_ERLANG_NEED_ERL (@ovar{path}) @acindex{ERLANG_NEED_ERL} A simplified variant of the @code{AC_ERLANG_PATH_ERL} macro, that prints an error message and exits the @command{configure} script if the @command{erl} program is not found. @end defmac @node Fortran Compiler @subsection Fortran Compiler Characteristics @cindex Fortran @cindex F77 The Autoconf Fortran support is divided into two categories: legacy Fortran 77 macros (@code{F77}), and modern Fortran macros (@code{FC}). The former are intended for traditional Fortran 77 code, and have output variables like @code{F77}, @code{FFLAGS}, and @code{FLIBS}. The latter are for newer programs that can (or must) compile under the newer Fortran standards, and have output variables like @code{FC}, @code{FCFLAGS}, and @code{FCLIBS}. Except for two new macros @code{AC_FC_SRCEXT} and @code{AC_FC_FREEFORM} (see below), the @code{FC} and @code{F77} macros behave almost identically, and so they are documented together in this section. @defmac AC_PROG_F77 (@ovar{compiler-search-list}) @acindex{PROG_F77} @ovindex F77 @ovindex FFLAGS Determine a Fortran 77 compiler to use. If @code{F77} is not already set in the environment, then check for @code{g77} and @code{f77}, and then some other names. Set the output variable @code{F77} to the name of the compiler found. This macro may, however, be invoked with an optional first argument which, if specified, must be a blank-separated list of Fortran 77 compilers to search for. This just gives the user an opportunity to specify an alternative search list for the Fortran 77 compiler. For example, if you didn't like the default order, then you could invoke @code{AC_PROG_F77} like this: @example AC_PROG_F77([fl32 f77 fort77 xlf g77 f90 xlf90]) @end example If using @code{g77} (the @acronym{GNU} Fortran 77 compiler), then set the shell variable @code{G77} to @samp{yes}. If the output variable @code{FFLAGS} was not already set in the environment, then set it to @option{-g -02} for @code{g77} (or @option{-O2} where @code{g77} does not accept @option{-g}). Otherwise, set @code{FFLAGS} to @option{-g} for all other Fortran 77 compilers. @end defmac @defmac AC_PROG_FC (@ovar{compiler-search-list}, @ovar{dialect}) @acindex{PROG_FC} @ovindex FC @ovindex FCFLAGS Determine a Fortran compiler to use. If @code{FC} is not already set in the environment, then @code{dialect} is a hint to indicate what Fortran dialect to search for; the default is to search for the newest available dialect. Set the output variable @code{FC} to the name of the compiler found. By default, newer dialects are preferred over older dialects, but if @code{dialect} is specified then older dialects are preferred starting with the specified dialect. @code{dialect} can currently be one of Fortran 77, Fortran 90, or Fortran 95. However, this is only a hint of which compiler @emph{name} to prefer (e.g., @code{f90} or @code{f95}), and no attempt is made to guarantee that a particular language standard is actually supported. Thus, it is preferable that you avoid the @code{dialect} option, and use AC_PROG_FC only for code compatible with the latest Fortran standard. This macro may, alternatively, be invoked with an optional first argument which, if specified, must be a blank-separated list of Fortran compilers to search for, just as in @code{AC_PROG_F77}. If the output variable @code{FCFLAGS} was not already set in the environment, then set it to @option{-g -02} for @acronym{GNU} @code{g77} (or @option{-O2} where @code{g77} does not accept @option{-g}). Otherwise, set @code{FCFLAGS} to @option{-g} for all other Fortran compilers. @end defmac @defmac AC_PROG_F77_C_O @defmacx AC_PROG_FC_C_O @acindex{PROG_F77_C_O} @acindex{PROG_FC_C_O} @cvindex F77_NO_MINUS_C_MINUS_O @cvindex FC_NO_MINUS_C_MINUS_O Test whether the Fortran compiler accepts the options @option{-c} and @option{-o} simultaneously, and define @code{F77_NO_MINUS_C_MINUS_O} or @code{FC_NO_MINUS_C_MINUS_O}, respectively, if it does not. @end defmac The following macros check for Fortran compiler characteristics. To check for characteristics not listed here, use @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}) or @code{AC_RUN_IFELSE} (@pxref{Runtime}), making sure to first set the current language to Fortran 77 or Fortran via @code{AC_LANG([Fortran 77])} or @code{AC_LANG(Fortran)} (@pxref{Language Choice}). @defmac AC_F77_LIBRARY_LDFLAGS @defmacx AC_FC_LIBRARY_LDFLAGS @acindex{F77_LIBRARY_LDFLAGS} @ovindex FLIBS @acindex{FC_LIBRARY_LDFLAGS} @ovindex FCLIBS Determine the linker flags (e.g., @option{-L} and @option{-l}) for the @dfn{Fortran intrinsic and runtime libraries} that are required to successfully link a Fortran program or shared library. The output variable @code{FLIBS} or @code{FCLIBS} is set to these flags (which should be included after @code{LIBS} when linking). This macro is intended to be used in those situations when it is necessary to mix, e.g., C++ and Fortran source code in a single program or shared library (@pxref{Mixing Fortran 77 With C and C++, , , automake, @acronym{GNU} Automake}). For example, if object files from a C++ and Fortran compiler must be linked together, then the C++ compiler/linker must be used for linking (since special C++-ish things need to happen at link time like calling global constructors, instantiating templates, enabling exception support, etc.). However, the Fortran intrinsic and runtime libraries must be linked in as well, but the C++ compiler/linker doesn't know by default how to add these Fortran 77 libraries. Hence, this macro was created to determine these Fortran libraries. The macros @code{AC_F77_DUMMY_MAIN} and @code{AC_FC_DUMMY_MAIN} or @code{AC_F77_MAIN} and @code{AC_FC_MAIN} are probably also necessary to link C/C++ with Fortran; see below. @end defmac @defmac AC_F77_DUMMY_MAIN (@ovar{action-if-found}, @ovar{action-if-not-found}) @defmacx AC_FC_DUMMY_MAIN (@ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{F77_DUMMY_MAIN} @cvindex F77_DUMMY_MAIN With many compilers, the Fortran libraries detected by @code{AC_F77_LIBRARY_LDFLAGS} or @code{AC_FC_LIBRARY_LDFLAGS} provide their own @code{main} entry function that initializes things like Fortran I/O, and which then calls a user-provided entry function named (say) @code{MAIN__} to run the user's program. The @code{AC_F77_DUMMY_MAIN} and @code{AC_FC_DUMMY_MAIN} or @code{AC_F77_MAIN} and @code{AC_FC_MAIN} macros figure out how to deal with this interaction. When using Fortran for purely numerical functions (no I/O, etc.)@: often one prefers to provide one's own @code{main} and skip the Fortran library initializations. In this case, however, one may still need to provide a dummy @code{MAIN__} routine in order to prevent linking errors on some systems. @code{AC_F77_DUMMY_MAIN} or @code{AC_FC_DUMMY_MAIN} detects whether any such routine is @emph{required} for linking, and what its name is; the shell variable @code{F77_DUMMY_MAIN} or @code{FC_DUMMY_MAIN} holds this name, @code{unknown} when no solution was found, and @code{none} when no such dummy main is needed. By default, @var{action-if-found} defines @code{F77_DUMMY_MAIN} or @code{FC_DUMMY_MAIN} to the name of this routine (e.g., @code{MAIN__}) @emph{if} it is required. @var{action-if-not-found} defaults to exiting with an error. In order to link with Fortran routines, the user's C/C++ program should then include the following code to define the dummy main if it is needed: @example #ifdef F77_DUMMY_MAIN # ifdef __cplusplus extern "C" # endif int F77_DUMMY_MAIN() @{ return 1; @} #endif @end example (Replace @code{F77} with @code{FC} for Fortran instead of Fortran 77.) Note that this macro is called automatically from @code{AC_F77_WRAPPERS} or @code{AC_FC_WRAPPERS}; there is generally no need to call it explicitly unless one wants to change the default actions. @end defmac @defmac AC_F77_MAIN @defmacx AC_FC_MAIN @acindex{F77_MAIN} @cvindex F77_MAIN @acindex{FC_MAIN} @cvindex FC_MAIN As discussed above, many Fortran libraries allow you to provide an entry point called (say) @code{MAIN__} instead of the usual @code{main}, which is then called by a @code{main} function in the Fortran libraries that initializes things like Fortran I/O@. The @code{AC_F77_MAIN} and @code{AC_FC_MAIN} macros detect whether it is @emph{possible} to utilize such an alternate main function, and defines @code{F77_MAIN} and @code{FC_MAIN} to the name of the function. (If no alternate main function name is found, @code{F77_MAIN} and @code{FC_MAIN} are simply defined to @code{main}.) Thus, when calling Fortran routines from C that perform things like I/O, one should use this macro and name the "main" function @code{F77_MAIN} or @code{FC_MAIN} instead of @code{main}. @end defmac @defmac AC_F77_WRAPPERS @defmacx AC_FC_WRAPPERS @acindex{F77_WRAPPERS} @cvindex F77_FUNC @cvindex F77_FUNC_ @acindex{FC_WRAPPERS} @cvindex FC_FUNC @cvindex FC_FUNC_ Defines C macros @code{F77_FUNC (name, NAME)}, @code{FC_FUNC (name, NAME)}, @code{F77_FUNC_(name, NAME)}, and @code{FC_FUNC_(name, NAME)} to properly mangle the names of C/C++ identifiers, and identifiers with underscores, respectively, so that they match the name-mangling scheme used by the Fortran compiler. Fortran is case-insensitive, and in order to achieve this the Fortran compiler converts all identifiers into a canonical case and format. To call a Fortran subroutine from C or to write a C function that is callable from Fortran, the C program must explicitly use identifiers in the format expected by the Fortran compiler. In order to do this, one simply wraps all C identifiers in one of the macros provided by @code{AC_F77_WRAPPERS} or @code{AC_FC_WRAPPERS}. For example, suppose you have the following Fortran 77 subroutine: @example subroutine foobar (x, y) double precision x, y y = 3.14159 * x return end @end example You would then declare its prototype in C or C++ as: @example #define FOOBAR_F77 F77_FUNC (foobar, FOOBAR) #ifdef __cplusplus extern "C" /* prevent C++ name mangling */ #endif void FOOBAR_F77(double *x, double *y); @end example Note that we pass both the lowercase and uppercase versions of the function name to @code{F77_FUNC} so that it can select the right one. Note also that all parameters to Fortran 77 routines are passed as pointers (@pxref{Mixing Fortran 77 With C and C++, , , automake, @acronym{GNU} Automake}). (Replace @code{F77} with @code{FC} for Fortran instead of Fortran 77.) Although Autoconf tries to be intelligent about detecting the name-mangling scheme of the Fortran compiler, there may be Fortran compilers that it doesn't support yet. In this case, the above code generates a compile-time error, but some other behavior (e.g., disabling Fortran-related features) can be induced by checking whether @code{F77_FUNC} or @code{FC_FUNC} is defined. Now, to call that routine from a C program, we would do something like: @example @{ double x = 2.7183, y; FOOBAR_F77 (&x, &y); @} @end example If the Fortran identifier contains an underscore (e.g., @code{foo_bar}), you should use @code{F77_FUNC_} or @code{FC_FUNC_} instead of @code{F77_FUNC} or @code{FC_FUNC} (with the same arguments). This is because some Fortran compilers mangle names differently if they contain an underscore. @end defmac @defmac AC_F77_FUNC (@var{name}, @ovar{shellvar}) @defmacx AC_FC_FUNC (@var{name}, @ovar{shellvar}) @acindex{F77_FUNC} @acindex{FC_FUNC} Given an identifier @var{name}, set the shell variable @var{shellvar} to hold the mangled version @var{name} according to the rules of the Fortran linker (see also @code{AC_F77_WRAPPERS} or @code{AC_FC_WRAPPERS}). @var{shellvar} is optional; if it is not supplied, the shell variable is simply @var{name}. The purpose of this macro is to give the caller a way to access the name-mangling information other than through the C preprocessor as above, for example, to call Fortran routines from some language other than C/C++. @end defmac @defmac AC_FC_SRCEXT (@var{ext}, @ovar{action-if-success}, @ovar{action-if-failure}) @acindex{FC_SRCEXT} By default, the @code{FC} macros perform their tests using a @file{.f} extension for source-code files. Some compilers, however, only enable newer language features for appropriately named files, e.g., Fortran 90 features only for @file{.f90} files. On the other hand, some other compilers expect all source files to end in @file{.f} and require special flags to support other file name extensions. The @code{AC_FC_SRCEXT} macro deals with both of these issues. The @code{AC_FC_SRCEXT} tries to get the @code{FC} compiler to accept files ending with the extension .@var{ext} (i.e., @var{ext} does @emph{not} contain the dot). If any special compiler flags are needed for this, it stores them in the output variable @code{FCFLAGS_}@var{ext}. This extension and these flags are then used for all subsequent @code{FC} tests (until @code{AC_FC_SRCEXT} is called again). For example, you would use @code{AC_FC_SRCEXT(f90)} to employ the @file{.f90} extension in future tests, and it would set a @code{FCFLAGS_f90} output variable with any extra flags that are needed to compile such files. The @code{FCFLAGS_}@var{ext} can @emph{not} be simply absorbed into @code{FCFLAGS}, for two reasons based on the limitations of some compilers. First, only one @code{FCFLAGS_}@var{ext} can be used at a time, so files with different extensions must be compiled separately. Second, @code{FCFLAGS_}@var{ext} must appear @emph{immediately} before the source-code file name when compiling. So, continuing the example above, you might compile a @file{foo.f90} file in your makefile with the command: @example foo.o: foo.f90 $(FC) -c $(FCFLAGS) $(FCFLAGS_f90) '$(srcdir)/foo.f90' @end example If @code{AC_FC_SRCEXT} succeeds in compiling files with the @var{ext} extension, it calls @var{action-if-success} (defaults to nothing). If it fails, and cannot find a way to make the @code{FC} compiler accept such files, it calls @var{action-if-failure} (defaults to exiting with an error message). @end defmac @defmac AC_FC_FREEFORM (@ovar{action-if-success}, @ovar{action-if-failure}) @acindex{FC_FREEFORM} The @code{AC_FC_FREEFORM} tries to ensure that the Fortran compiler (@code{$FC}) allows free-format source code (as opposed to the older fixed-format style from Fortran 77). If necessary, it may add some additional flags to @code{FCFLAGS}. This macro is most important if you are using the default @file{.f} extension, since many compilers interpret this extension as indicating fixed-format source unless an additional flag is supplied. If you specify a different extension with @code{AC_FC_SRCEXT}, such as @file{.f90} or @file{.f95}, then @code{AC_FC_FREEFORM} ordinarily succeeds without modifying @code{FCFLAGS}. If @code{AC_FC_FREEFORM} succeeds in compiling free-form source, it calls @var{action-if-success} (defaults to nothing). If it fails, it calls @var{action-if-failure} (defaults to exiting with an error message). @end defmac @node System Services @section System Services The following macros check for operating system services or capabilities. @defmac AC_PATH_X @acindex{PATH_X} @evindex XMKMF @cindex X Window System Try to locate the X Window System include files and libraries. If the user gave the command line options @option{--x-includes=@var{dir}} and @option{--x-libraries=@var{dir}}, use those directories. If either or both were not given, get the missing values by running @code{xmkmf} (or an executable pointed to by the @code{XMKMF} environment variable) on a trivial @file{Imakefile} and examining the makefile that it produces. Setting @code{XMKMF} to @samp{false} disables this method. If this method fails to find the X Window System, @command{configure} looks for the files in several directories where they often reside. If either method is successful, set the shell variables @code{x_includes} and @code{x_libraries} to their locations, unless they are in directories the compiler searches by default. If both methods fail, or the user gave the command line option @option{--without-x}, set the shell variable @code{no_x} to @samp{yes}; otherwise set it to the empty string. @end defmac @defmac AC_PATH_XTRA @acindex{PATH_XTRA} @ovindex X_CFLAGS @ovindex X_LIBS @ovindex X_EXTRA_LIBS @ovindex X_PRE_LIBS @cvindex X_DISPLAY_MISSING An enhanced version of @code{AC_PATH_X}. It adds the C compiler flags that X needs to output variable @code{X_CFLAGS}, and the X linker flags to @code{X_LIBS}. Define @code{X_DISPLAY_MISSING} if X is not available. This macro also checks for special libraries that some systems need in order to compile X programs. It adds any that the system needs to output variable @code{X_EXTRA_LIBS}. And it checks for special X11R6 libraries that need to be linked with before @option{-lX11}, and adds any found to the output variable @code{X_PRE_LIBS}. @c This is an incomplete kludge. Make a real way to do it. @c If you need to check for other X functions or libraries yourself, then @c after calling this macro, add the contents of @code{X_EXTRA_LIBS} to @c @code{LIBS} temporarily, like this: (FIXME - add example) @end defmac @defmac AC_SYS_INTERPRETER @acindex{SYS_INTERPRETER} Check whether the system supports starting scripts with a line of the form @samp{#!/bin/sh} to select the interpreter to use for the script. After running this macro, shell code in @file{configure.ac} can check the shell variable @code{interpval}; it is set to @samp{yes} if the system supports @samp{#!}, @samp{no} if not. @end defmac @defmac AC_SYS_LARGEFILE @acindex{SYS_LARGEFILE} @cvindex _FILE_OFFSET_BITS @cvindex _LARGE_FILES @ovindex CC @cindex Large file support @cindex LFS Arrange for @uref{http://www.unix-systems.org/@/version2/@/whatsnew/@/lfs20mar.html, large-file support}. On some hosts, one must use special compiler options to build programs that can access large files. Append any such options to the output variable @code{CC}. Define @code{_FILE_OFFSET_BITS} and @code{_LARGE_FILES} if necessary. Large-file support can be disabled by configuring with the @option{--disable-largefile} option. If you use this macro, check that your program works even when @code{off_t} is wider than @code{long int}, since this is common when large-file support is enabled. For example, it is not correct to print an arbitrary @code{off_t} value @code{X} with @code{printf ("%ld", (long int) X)}. The LFS introduced the @code{fseeko} and @code{ftello} functions to replace their C counterparts @code{fseek} and @code{ftell} that do not use @code{off_t}. Take care to use @code{AC_FUNC_FSEEKO} to make their prototypes available when using them and large-file support is enabled. @end defmac @defmac AC_SYS_LONG_FILE_NAMES @acindex{SYS_LONG_FILE_NAMES} @cvindex HAVE_LONG_FILE_NAMES If the system supports file names longer than 14 characters, define @code{HAVE_LONG_FILE_NAMES}. @end defmac @defmac AC_SYS_POSIX_TERMIOS @acindex{SYS_POSIX_TERMIOS} @cindex Posix termios headers @cindex termios Posix headers Check to see if the Posix termios headers and functions are available on the system. If so, set the shell variable @code{ac_cv_sys_posix_termios} to @samp{yes}. If not, set the variable to @samp{no}. @end defmac @node Posix Variants @section Posix Variants The following macros check for certain operating systems that need special treatment for some programs, due to exceptional oddities in their header files or libraries. These macros are warts; they will be replaced by a more systematic approach, based on the functions they make available or the environments they provide. @defmac AC_AIX @acindex{AIX} @cvindex _ALL_SOURCE If on @acronym{AIX}, define @code{_ALL_SOURCE}. Allows the use of some @acronym{BSD} functions. Should be called before any macros that run the C compiler. @end defmac @defmac AC_GNU_SOURCE @acindex{GNU_SOURCE} @cvindex _GNU_SOURCE If using the @acronym{GNU} C library, define @code{_GNU_SOURCE}. Allows the use of some @acronym{GNU} functions. Should be called before any macros that run the C compiler. @end defmac @defmac AC_ISC_POSIX @acindex{ISC_POSIX} @ovindex LIBS For @sc{interactive} Systems Corporation Unix, add @option{-lcposix} to output variable @code{LIBS} if necessary for Posix facilities. Call this after @code{AC_PROG_CC} and before any other macros that use Posix interfaces. This macro is obsolescent, as @sc{interactive} Unix is obsolete, and Sun dropped support for it on 2006-07-23. New programs need not use this macro. @end defmac @defmac AC_MINIX @acindex{MINIX} @cvindex _MINIX @cvindex _POSIX_SOURCE @cvindex _POSIX_1_SOURCE If on Minix, define @code{_MINIX} and @code{_POSIX_SOURCE} and define @code{_POSIX_1_SOURCE} to be 2. This allows the use of Posix facilities. Should be called before any macros that run the C compiler. @end defmac @defmac AC_USE_SYSTEM_EXTENSIONS @acindex{USE_SYSTEM_EXTENSIONS} @cvindex _ALL_SOURCE @cvindex _GNU_SOURCE @cvindex _MINIX @cvindex _POSIX_1_SOURCE @cvindex _POSIX_PTHREAD_SEMANTICS @cvindex _POSIX_SOURCE @cvindex _TANDEM_SOURCE @cvindex __EXTENSIONS__ If possible, enable extensions to Posix on hosts that normally disable the extensions, typically due to standards-conformance namespace issues. This may involve defining @code{__EXTENSIONS__} and @code{_POSIX_PTHREAD_SEMANTICS}, which are macros used by Solaris. It also defines @code{_TANDEM_SOURCE} for the @acronym{HP} NonStop platform. This macro also has the combined effects of @code{AC_GNU_SOURCE}, @code{AC_AIX}, and @code{AC_MINIX}. @end defmac @node Erlang Libraries @section Erlang Libraries @cindex Erlang, Library, checking The following macros check for an installation of Erlang/OTP, and for the presence of certain Erlang libraries. All those macros require the configuration of an Erlang interpreter and an Erlang compiler (@pxref{Erlang Compiler and Interpreter}). @defmac AC_ERLANG_SUBST_ROOT_DIR @acindex{ERLANG_SUBST_ROOT_DIR} @ovindex ERLANG_ROOT_DIR Set the output variable @code{ERLANG_ROOT_DIR} to the path to the base directory in which Erlang/OTP is installed (as returned by Erlang's @code{code:root_dir/0} function). The result of this test is cached if caching is enabled when running @command{configure}. @end defmac @defmac AC_ERLANG_SUBST_LIB_DIR @acindex{ERLANG_SUBST_LIB_DIR} @ovindex ERLANG_LIB_DIR Set the output variable @code{ERLANG_LIB_DIR} to the path of the library directory of Erlang/OTP (as returned by Erlang's @code{code:lib_dir/0} function), which subdirectories each contain an installed Erlang/OTP library. The result of this test is cached if caching is enabled when running @command{configure}. @end defmac @defmac AC_ERLANG_CHECK_LIB (@var{library}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{ERLANG_CHECK_LIB} @ovindex ERLANG_LIB_DIR_@var{library} @ovindex ERLANG_LIB_VER_@var{library} Test whether the Erlang/OTP library @var{library} is installed by calling Erlang's @code{code:lib_dir/1} function. The result of this test is cached if caching is enabled when running @command{configure}. @var{action-if-found} is a list of shell commands to run if the library is installed; @var{action-if-not-found} is a list of shell commands to run if it is not. Additionally, if the library is installed, the output variable @samp{ERLANG_LIB_DIR_@var{library}} is set to the path to the library installation directory, and the output variable @samp{ERLANG_LIB_VER_@var{library}} is set to the version number that is part of the subdirectory name, if it is in the standard form (@code{@var{library}-@var{version}}). If the directory name does not have a version part, @samp{ERLANG_LIB_VER_@var{library}} is set to the empty string. If the library is not installed, @samp{ERLANG_LIB_DIR_@var{library}} and @samp{ERLANG_LIB_VER_@var{library}} are set to @code{"not found"}. For example, to check if library @code{stdlib} is installed: @example AC_ERLANG_CHECK_LIB([stdlib], [echo "stdlib version \"$ERLANG_LIB_VER_stdlib\"" echo "is installed in \"$ERLANG_LIB_DIR_stdlib\""], [AC_MSG_ERROR([stdlib was not found!])]) @end example @end defmac In addition to the above macros, which test installed Erlang libraries, the following macros determine the paths to the directories into which newly built Erlang libraries are to be installed: @defmac AC_ERLANG_SUBST_INSTALL_LIB_DIR @acindex{ERLANG_SUBST_INSTALL_LIB_DIR} @ovindex ERLANG_INSTALL_LIB_DIR Set the @code{ERLANG_INSTALL_LIB_DIR} output variable to the directory into which every built Erlang library should be installed in a separate subdirectory. If this variable is not set in the environment when @command{configure} runs, its default value is @code{$ERLANG_LIB_DIR}, which value is set by the @code{AC_ERLANG_SUBST_LIB_DIR} macro. @end defmac @defmac AC_ERLANG_SUBST_INSTALL_LIB_SUBDIR (@var{library}, @var{version}) @acindex{ERLANG_SUBST_INSTALL_LIB_SUBDIR} @ovindex ERLANG_INSTALL_LIB_DIR_@var{library} Set the @samp{ERLANG_INSTALL_LIB_DIR_@var{library}} output variable to the directory into which the built Erlang library @var{library} version @var{version} should be installed. If this variable is not set in the environment when @command{configure} runs, its default value is @samp{$ERLANG_INSTALL_LIB_DIR/@var{library}-@var{version}}, the value of the @code{ERLANG_INSTALL_LIB_DIR} variable being set by the @code{AC_ERLANG_SUBST_INSTALL_LIB_DIR} macro. @end defmac @c ========================================================= Writing Tests @node Writing Tests @chapter Writing Tests If the existing feature tests don't do something you need, you have to write new ones. These macros are the building blocks. They provide ways for other macros to check whether various kinds of features are available and report the results. This chapter contains some suggestions and some of the reasons why the existing tests are written the way they are. You can also learn a lot about how to write Autoconf tests by looking at the existing ones. If something goes wrong in one or more of the Autoconf tests, this information can help you understand the assumptions behind them, which might help you figure out how to best solve the problem. These macros check the output of the compiler system of the current language (@pxref{Language Choice}). They do not cache the results of their tests for future use (@pxref{Caching Results}), because they don't know enough about the information they are checking for to generate a cache variable name. They also do not print any messages, for the same reason. The checks for particular kinds of features call these macros and do cache their results and print messages about what they're checking for. When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. @xref{Writing Autoconf Macros}, for how to do that. @menu * Language Choice:: Selecting which language to use for testing * Writing Test Programs:: Forging source files for compilers * Running the Preprocessor:: Detecting preprocessor symbols * Running the Compiler:: Detecting language or header features * Running the Linker:: Detecting library features * Runtime:: Testing for runtime features * Systemology:: A zoology of operating systems * Multiple Cases:: Tests for several possible values @end menu @node Language Choice @section Language Choice @cindex Language Autoconf-generated @command{configure} scripts check for the C compiler and its features by default. Packages that use other programming languages (maybe more than one, e.g., C and C++) need to test features of the compilers for the respective languages. The following macros determine which programming language is used in the subsequent tests in @file{configure.ac}. @defmac AC_LANG (@var{language}) Do compilation tests using the compiler, preprocessor, and file extensions for the specified @var{language}. Supported languages are: @table @samp @item C Do compilation tests using @code{CC} and @code{CPP} and use extension @file{.c} for test programs. Use compilation flags: @code{CPPFLAGS} with @code{CPP}, and both @code{CPPFLAGS} and @code{CFLAGS} with @code{CC}. @item C++ Do compilation tests using @code{CXX} and @code{CXXCPP} and use extension @file{.C} for test programs. Use compilation flags: @code{CPPFLAGS} with @code{CXXPP}, and both @code{CPPFLAGS} and @code{CXXFLAGS} with @code{CXX}. @item Fortran 77 Do compilation tests using @code{F77} and use extension @file{.f} for test programs. Use compilation flags: @code{FFLAGS}. @item Fortran Do compilation tests using @code{FC} and use extension @file{.f} (or whatever has been set by @code{AC_FC_SRCEXT}) for test programs. Use compilation flags: @code{FCFLAGS}. @item Erlang @ovindex ERLC @ovindex ERL @ovindex ERLCFLAGS Compile and execute tests using @code{ERLC} and @code{ERL} and use extension @file{.erl} for test Erlang modules. Use compilation flags: @code{ERLCFLAGS}. @item Objective C Do compilation tests using @code{OBJC} and @code{OBJCCPP} and use extension @file{.m} for test programs. Use compilation flags: @code{CPPFLAGS} with @code{OBJCPP}, and both @code{CPPFLAGS} and @code{OBJCFLAGS} with @code{OBJC}. @end table @end defmac @defmac AC_LANG_PUSH (@var{language}) @acindex{LANG_PUSH} Remember the current language (as set by @code{AC_LANG}) on a stack, and then select the @var{language}. Use this macro and @code{AC_LANG_POP} in macros that need to temporarily switch to a particular language. @end defmac @defmac AC_LANG_POP (@ovar{language}) @acindex{LANG_POP} Select the language that is saved on the top of the stack, as set by @code{AC_LANG_PUSH}, and remove it from the stack. If given, @var{language} specifies the language we just @emph{quit}. It is a good idea to specify it when it's known (which should be the case@dots{}), since Autoconf detects inconsistencies. @example AC_LANG_PUSH([Fortran 77]) # Perform some tests on Fortran 77. # @dots{} AC_LANG_POP([Fortran 77]) @end example @end defmac @defmac AC_LANG_ASSERT (@var{language}) @acindex{LANG_ASSERT} Check statically that the current language is @var{language}. You should use this in your language specific macros to avoid that they be called with an inappropriate language. This macro runs only at @command{autoconf} time, and incurs no cost at @command{configure} time. Sadly enough and because Autoconf is a two layer language @footnote{Because M4 is not aware of Sh code, especially conditionals, some optimizations that look nice statically may produce incorrect results at runtime.}, the macros @code{AC_LANG_PUSH} and @code{AC_LANG_POP} cannot be ``optimizing'', therefore as much as possible you ought to avoid using them to wrap your code, rather, require from the user to run the macro with a correct current language, and check it with @code{AC_LANG_ASSERT}. And anyway, that may help the user understand she is running a Fortran macro while expecting a result about her Fortran 77 compiler@dots{} @end defmac @defmac AC_REQUIRE_CPP @acindex{REQUIRE_CPP} Ensure that whichever preprocessor would currently be used for tests has been found. Calls @code{AC_REQUIRE} (@pxref{Prerequisite Macros}) with an argument of either @code{AC_PROG_CPP} or @code{AC_PROG_CXXCPP}, depending on which language is current. @end defmac @node Writing Test Programs @section Writing Test Programs Autoconf tests follow a common scheme: feed some program with some input, and most of the time, feed a compiler with some source file. This section is dedicated to these source samples. @menu * Guidelines:: General rules for writing test programs * Test Functions:: Avoiding pitfalls in test programs * Generating Sources:: Source program boilerplate @end menu @node Guidelines @subsection Guidelines for Test Programs The most important rule to follow when writing testing samples is: @center @emph{Look for realism.} This motto means that testing samples must be written with the same strictness as real programs are written. In particular, you should avoid ``shortcuts'' and simplifications. Don't just play with the preprocessor if you want to prepare a compilation. For instance, using @command{cpp} to check whether a header is functional might let your @command{configure} accept a header which causes some @emph{compiler} error. Do not hesitate to check a header with other headers included before, especially required headers. Make sure the symbols you use are properly defined, i.e., refrain for simply declaring a function yourself instead of including the proper header. Test programs should not write to standard output. They should exit with status 0 if the test succeeds, and with status 1 otherwise, so that success can be distinguished easily from a core dump or other failure; segmentation violations and other failures produce a nonzero exit status. Unless you arrange for @code{exit} to be declared, test programs should @code{return}, not @code{exit}, from @code{main}, because on many systems @code{exit} is not declared by default. Test programs can use @code{#if} or @code{#ifdef} to check the values of preprocessor macros defined by tests that have already run. For example, if you call @code{AC_HEADER_STDBOOL}, then later on in @file{configure.ac} you can have a test program that includes @file{stdbool.h} conditionally: @example @group #ifdef HAVE_STDBOOL_H # include #endif @end group @end example Both @code{#if HAVE_STDBOOL_H} and @code{#ifdef HAVE_STDBOOL_H} will work with any standard C compiler. Some developers prefer @code{#if} because it is easier to read, while others prefer @code{#ifdef} because it avoids diagnostics with picky compilers like @acronym{GCC} with the @option{-Wundef} option. If a test program needs to use or create a data file, give it a name that starts with @file{conftest}, such as @file{conftest.data}. The @command{configure} script cleans up by running @samp{rm -f -r conftest*} after running test programs and if the script is interrupted. @node Test Functions @subsection Test Functions These days it's safe to assume support for function prototypes (introduced in C89). Functions that test programs declare should also be conditionalized for C++, which requires @samp{extern "C"} prototypes. Make sure to not include any header files containing clashing prototypes. @example #ifdef __cplusplus extern "C" #endif void *valloc (size_t); @end example If a test program calls a function with invalid parameters (just to see whether it exists), organize the program to ensure that it never invokes that function. You can do this by calling it in another function that is never invoked. You can't do it by putting it after a call to @code{exit}, because @acronym{GCC} version 2 knows that @code{exit} never returns and optimizes out any code that follows it in the same block. If you include any header files, be sure to call the functions relevant to them with the correct number of arguments, even if they are just 0, to avoid compilation errors due to prototypes. @acronym{GCC} version 2 has internal prototypes for several functions that it automatically inlines; for example, @code{memcpy}. To avoid errors when checking for them, either pass them the correct number of arguments or redeclare them with a different return type (such as @code{char}). @node Generating Sources @subsection Generating Sources Autoconf provides a set of macros that can be used to generate test source files. They are written to be language generic, i.e., they actually depend on the current language (@pxref{Language Choice}) to ``format'' the output properly. @defmac AC_LANG_CONFTEST (@var{source}) @acindex{LANG_CONFTEST} Save the @var{source} text in the current test source file: @file{conftest.@var{extension}} where the @var{extension} depends on the current language. Note that the @var{source} is evaluated exactly once, like regular Autoconf macro arguments, and therefore (i) you may pass a macro invocation, (ii) if not, be sure to double quote if needed. @end defmac @defmac AC_LANG_SOURCE (@var{source}) @acindex{LANG_SOURCE} Expands into the @var{source}, with the definition of all the @code{AC_DEFINE} performed so far. @end defmac For instance executing (observe the double quotation!): @example AC_INIT([Hello], [1.0], [bug-hello@@example.org]) AC_DEFINE([HELLO_WORLD], ["Hello, World\n"], [Greetings string.]) AC_LANG(C) AC_LANG_CONFTEST( [AC_LANG_SOURCE([[const char hw[] = "Hello, World\n";]])]) gcc -E -dD -o - conftest.c @end example @noindent results in: @example @dots{} # 1 "conftest.c" #define PACKAGE_NAME "Hello" #define PACKAGE_TARNAME "hello" #define PACKAGE_VERSION "1.0" #define PACKAGE_STRING "Hello 1.0" #define PACKAGE_BUGREPORT "bug-hello@@example.org" #define HELLO_WORLD "Hello, World\n" const char hw[] = "Hello, World\n"; @end example When the test language is Fortran or Erlang, the @code{AC_DEFINE} definitions are not automatically translated into constants in the source code by this macro. @defmac AC_LANG_PROGRAM (@var{prologue}, @var{body}) @acindex{LANG_PROGRAM} Expands into a source file which consists of the @var{prologue}, and then @var{body} as body of the main function (e.g., @code{main} in C). Since it uses @code{AC_LANG_SOURCE}, the features of the latter are available. @end defmac For instance: @example AC_INIT([Hello], [1.0], [bug-hello@@example.org]) AC_DEFINE([HELLO_WORLD], ["Hello, World\n"], [Greetings string.]) AC_LANG_CONFTEST( [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]], [[fputs (hw, stdout);]])]) gcc -E -dD -o - conftest.c @end example @noindent results in: @example @dots{} # 1 "conftest.c" #define PACKAGE_NAME "Hello" #define PACKAGE_TARNAME "hello" #define PACKAGE_VERSION "1.0" #define PACKAGE_STRING "Hello 1.0" #define PACKAGE_BUGREPORT "bug-hello@@example.org" #define HELLO_WORLD "Hello, World\n" const char hw[] = "Hello, World\n"; int main () @{ fputs (hw, stdout); ; return 0; @} @end example In Erlang tests, the created source file is that of an Erlang module called @code{conftest} (@file{conftest.erl}). This module defines and exports at least one @code{start/0} function, which is called to perform the test. The @var{prologue} is optional code that is inserted between the module header and the @code{start/0} function definition. @var{body} is the body of the @code{start/0} function without the final period (@pxref{Runtime}, about constraints on this function's behavior). For instance: @example AC_INIT([Hello], [1.0], [bug-hello@@example.org]) AC_LANG(Erlang) AC_LANG_CONFTEST( [AC_LANG_PROGRAM([[-define(HELLO_WORLD, "Hello, world!").]], [[io:format("~s~n", [?HELLO_WORLD])]])]) cat conftest.erl @end example @noindent results in: @example -module(conftest). -export([start/0]). -define(HELLO_WORLD, "Hello, world!"). start() -> io:format("~s~n", [?HELLO_WORLD]) . @end example @defmac AC_LANG_CALL (@var{prologue}, @var{function}) @acindex{LANG_CALL} Expands into a source file which consists of the @var{prologue}, and then a call to the @var{function} as body of the main function (e.g., @code{main} in C). Since it uses @code{AC_LANG_PROGRAM}, the feature of the latter are available. This function will probably be replaced in the future by a version which would enable specifying the arguments. The use of this macro is not encouraged, as it violates strongly the typing system. This macro cannot be used for Erlang tests. @end defmac @defmac AC_LANG_FUNC_LINK_TRY (@var{function}) @acindex{LANG_FUNC_LINK_TRY} Expands into a source file which uses the @var{function} in the body of the main function (e.g., @code{main} in C). Since it uses @code{AC_LANG_PROGRAM}, the features of the latter are available. As @code{AC_LANG_CALL}, this macro is documented only for completeness. It is considered to be severely broken, and in the future will be removed in favor of actual function calls (with properly typed arguments). This macro cannot be used for Erlang tests. @end defmac @node Running the Preprocessor @section Running the Preprocessor Sometimes one might need to run the preprocessor on some source file. @emph{Usually it is a bad idea}, as you typically need to @emph{compile} your project, not merely run the preprocessor on it; therefore you certainly want to run the compiler, not the preprocessor. Resist the temptation of following the easiest path. Nevertheless, if you need to run the preprocessor, then use @code{AC_PREPROC_IFELSE}. The macros described in this section cannot be used for tests in Erlang or Fortran, since those languages require no preprocessor. @defmac AC_PREPROC_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false}) @acindex{PREPROC_IFELSE} Run the preprocessor of the current language (@pxref{Language Choice}) on the @var{input}, run the shell commands @var{action-if-true} on success, @var{action-if-false} otherwise. The @var{input} can be made by @code{AC_LANG_PROGRAM} and friends. This macro uses @code{CPPFLAGS}, but not @code{CFLAGS}, because @option{-g}, @option{-O}, etc.@: are not valid options to many C preprocessors. It is customary to report unexpected failures with @code{AC_MSG_FAILURE}. @end defmac For instance: @example AC_INIT([Hello], [1.0], [bug-hello@@example.org]) AC_DEFINE([HELLO_WORLD], ["Hello, World\n"], [Greetings string.]) AC_PREPROC_IFELSE( [AC_LANG_PROGRAM([[const char hw[] = "Hello, World\n";]], [[fputs (hw, stdout);]])], [AC_MSG_RESULT([OK])], [AC_MSG_FAILURE([unexpected preprocessor failure])]) @end example @noindent results in: @example checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking how to run the C preprocessor... gcc -E OK @end example @sp 1 The macro @code{AC_TRY_CPP} (@pxref{Obsolete Macros}) used to play the role of @code{AC_PREPROC_IFELSE}, but double quotes its argument, making it impossible to use it to elaborate sources. You are encouraged to get rid of your old use of the macro @code{AC_TRY_CPP} in favor of @code{AC_PREPROC_IFELSE}, but, in the first place, are you sure you need to run the @emph{preprocessor} and not the compiler? @defmac AC_EGREP_HEADER (@var{pattern}, @var{header-file}, @var{action-if-found}, @ovar{action-if-not-found}) @acindex{EGREP_HEADER} If the output of running the preprocessor on the system header file @var{header-file} matches the extended regular expression @var{pattern}, execute shell commands @var{action-if-found}, otherwise execute @var{action-if-not-found}. @end defmac @defmac AC_EGREP_CPP (@var{pattern}, @var{program}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{EGREP_CPP} @var{program} is the text of a C or C++ program, on which shell variable, back quote, and backslash substitutions are performed. If the output of running the preprocessor on @var{program} matches the extended regular expression @var{pattern}, execute shell commands @var{action-if-found}, otherwise execute @var{action-if-not-found}. @end defmac @node Running the Compiler @section Running the Compiler To check for a syntax feature of the current language's (@pxref{Language Choice}) compiler, such as whether it recognizes a certain keyword, or simply to try some library feature, use @code{AC_COMPILE_IFELSE} to try to compile a small program that uses that feature. @defmac AC_COMPILE_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false}) @acindex{COMPILE_IFELSE} Run the compiler and compilation flags of the current language (@pxref{Language Choice}) on the @var{input}, run the shell commands @var{action-if-true} on success, @var{action-if-false} otherwise. The @var{input} can be made by @code{AC_LANG_PROGRAM} and friends. It is customary to report unexpected failures with @code{AC_MSG_FAILURE}. This macro does not try to link; use @code{AC_LINK_IFELSE} if you need to do that (@pxref{Running the Linker}). @end defmac @ovindex ERL For tests in Erlang, the @var{input} must be the source code of a module named @code{conftest}. @code{AC_COMPILE_IFELSE} generates a @file{conftest.beam} file that can be interpreted by the Erlang virtual machine (@code{ERL}). It is recommended to use @code{AC_LANG_PROGRAM} to specify the test program, to ensure that the Erlang module has the right name. @node Running the Linker @section Running the Linker To check for a library, a function, or a global variable, Autoconf @command{configure} scripts try to compile and link a small program that uses it. This is unlike Metaconfig, which by default uses @code{nm} or @code{ar} on the C library to try to figure out which functions are available. Trying to link with the function is usually a more reliable approach because it avoids dealing with the variations in the options and output formats of @code{nm} and @code{ar} and in the location of the standard libraries. It also allows configuring for cross-compilation or checking a function's runtime behavior if needed. On the other hand, it can be slower than scanning the libraries once, but accuracy is more important than speed. @code{AC_LINK_IFELSE} is used to compile test programs to test for functions and global variables. It is also used by @code{AC_CHECK_LIB} to check for libraries (@pxref{Libraries}), by adding the library being checked for to @code{LIBS} temporarily and trying to link a small program. @defmac AC_LINK_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false}) @acindex{LINK_IFELSE} Run the compiler (and compilation flags) and the linker of the current language (@pxref{Language Choice}) on the @var{input}, run the shell commands @var{action-if-true} on success, @var{action-if-false} otherwise. The @var{input} can be made by @code{AC_LANG_PROGRAM} and friends. @code{LDFLAGS} and @code{LIBS} are used for linking, in addition to the current compilation flags. It is customary to report unexpected failures with @code{AC_MSG_FAILURE}. This macro does not try to execute the program; use @code{AC_RUN_IFELSE} if you need to do that (@pxref{Runtime}). @end defmac The @code{AC_LINK_IFELSE} macro cannot be used for Erlang tests, since Erlang programs are interpreted and do not require linking. @node Runtime @section Checking Runtime Behavior Sometimes you need to find out how a system performs at runtime, such as whether a given function has a certain capability or bug. If you can, make such checks when your program runs instead of when it is configured. You can check for things like the machine's endianness when your program initializes itself. If you really need to test for a runtime behavior while configuring, you can write a test program to determine the result, and compile and run it using @code{AC_RUN_IFELSE}. Avoid running test programs if possible, because this prevents people from configuring your package for cross-compiling. @defmac AC_RUN_IFELSE (@var{input}, @ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-cross-compiling}) @acindex{RUN_IFELSE} If @var{program} compiles and links successfully and returns an exit status of 0 when executed, run shell commands @var{action-if-true}. Otherwise, run shell commands @var{action-if-false}. The @var{input} can be made by @code{AC_LANG_PROGRAM} and friends. @code{LDFLAGS} and @code{LIBS} are used for linking, in addition to the compilation flags of the current language (@pxref{Language Choice}). If the compiler being used does not produce executables that run on the system where @command{configure} is being run, then the test program is not run. If the optional shell commands @var{action-if-cross-compiling} are given, they are run instead. Otherwise, @command{configure} prints an error message and exits. In the @var{action-if-false} section, the failing exit status is available in the shell variable @samp{$?}. This exit status might be that of a failed compilation, or it might be that of a failed program execution. It is customary to report unexpected failures with @code{AC_MSG_FAILURE}. @end defmac Try to provide a pessimistic default value to use when cross-compiling makes runtime tests impossible. You do this by passing the optional last argument to @code{AC_RUN_IFELSE}. @command{autoconf} prints a warning message when creating @command{configure} each time it encounters a call to @code{AC_RUN_IFELSE} with no @var{action-if-cross-compiling} argument given. You may ignore the warning, though users cannot configure your package for cross-compiling. A few of the macros distributed with Autoconf produce this warning message. To configure for cross-compiling you can also choose a value for those parameters based on the canonical system name (@pxref{Manual Configuration}). Alternatively, set up a test results cache file with the correct values for the host system (@pxref{Caching Results}). @ovindex cross_compiling To provide a default for calls of @code{AC_RUN_IFELSE} that are embedded in other macros, including a few of the ones that come with Autoconf, you can test whether the shell variable @code{cross_compiling} is set to @samp{yes}, and then use an alternate method to get the results instead of calling the macros. A C or C++ runtime test should be portable. @xref{Portable C and C++}. Erlang tests must exit themselves the Erlang VM by calling the @code{halt/1} function: the given status code is used to determine the success of the test (status is @code{0}) or its failure (status is different than @code{0}), as explained above. It must be noted that data output through the standard output (e.g., using @code{io:format/2}) may be truncated when halting the VM. Therefore, if a test must output configuration information, it is recommended to create and to output data into the temporary file named @file{conftest.out}, using the functions of module @code{file}. The @code{conftest.out} file is automatically deleted by the @code{AC_RUN_IFELSE} macro. For instance, a simplified implementation of Autoconf's @code{AC_ERLANG_SUBST_LIB_DIR} macro is: @example AC_INIT([LibdirTest], [1.0], [bug-libdirtest@@example.org]) AC_ERLANG_NEED_ERL AC_LANG(Erlang) AC_RUN_IFELSE( [AC_LANG_PROGRAM([], [dnl file:write_file("conftest.out", code:lib_dir()), halt(0)])], [echo "code:lib_dir() returned: `cat conftest.out`"], [AC_MSG_FAILURE([test Erlang program execution failed])]) @end example @node Systemology @section Systemology @cindex Systemology This section aims at presenting some systems and pointers to documentation. It may help you addressing particular problems reported by users. @uref{http://www.opengroup.org/susv3, Posix-conforming systems} are derived from the @uref{http://www.bell-labs.com/history/unix/, Unix operating system}. The @uref{http://bhami.com/rosetta.html, Rosetta Stone for Unix} contains a table correlating the features of various Posix-conforming systems. @uref{http://www.levenez.com/unix/, Unix History} is a simplified diagram of how many Unix systems were derived from each other. @uref{http://heirloom.sourceforge.net/, The Heirloom Project} provides some variants of traditional implementations of Unix utilities. @table @asis @item Darwin @cindex Darwin Darwin is also known as Mac OS X@. Beware that the file system @emph{can} be case-preserving, but case insensitive. This can cause nasty problems, since for instance the installation attempt for a package having an @file{INSTALL} file can result in @samp{make install} report that nothing was to be done! That's all dependent on whether the file system is a UFS (case sensitive) or HFS+ (case preserving). By default Apple wants you to install the OS on HFS+. Unfortunately, there are some pieces of software which really need to be built on UFS@. We may want to rebuild Darwin to have both UFS and HFS+ available (and put the /local/build tree on the UFS). @item @acronym{QNX} 4.25 @cindex @acronym{QNX} 4.25 @c FIXME: Please, if you feel like writing something more precise, @c it'd be great. In particular, I can't understand the difference with @c QNX Neutrino. @acronym{QNX} is a realtime operating system running on Intel architecture meant to be scalable from the small embedded systems to the hundred processor super-computer. It claims to be Posix certified. More information is available on the @uref{http://www.qnx.com/, @acronym{QNX} home page}. @item Tru64 @cindex Tru64 @uref{http://h30097.www3.hp.com/@/docs/, Documentation of several versions of Tru64} is available in different formats. @item Unix version 7 @cindex Unix version 7 @cindex V7 Officially this was called the ``Seventh Edition'' of ``the @sc{unix} time-sharing system'' but we use the more-common name ``Unix version 7''. Documentation is available in the @uref{http://plan9.bell-labs.com/@/7thEdMan/, Unix Seventh Edition Manual}. Previous versions of Unix are called ``Unix version 6'', etc., but they were not as widely used. @end table @node Multiple Cases @section Multiple Cases Some operations are accomplished in several possible ways, depending on the OS variant. Checking for them essentially requires a ``case statement''. Autoconf does not directly provide one; however, it is easy to simulate by using a shell variable to keep track of whether a way to perform the operation has been found yet. Here is an example that uses the shell variable @code{fstype} to keep track of whether the remaining cases need to be checked. @example @group AC_MSG_CHECKING([how to get file system type]) fstype=no # The order of these tests is important. AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include #include ]])], [AC_DEFINE([FSTYPE_STATVFS], [1], [Define if statvfs exists.]) fstype=SVR4]) if test $fstype = no; then AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include #include ]])], [AC_DEFINE([FSTYPE_USG_STATFS], [1], [Define if USG statfs.]) fstype=SVR3]) fi if test $fstype = no; then AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[#include #include ]])]), [AC_DEFINE([FSTYPE_AIX_STATFS], [1], [Define if AIX statfs.]) fstype=AIX]) fi # (more cases omitted here) AC_MSG_RESULT([$fstype]) @end group @end example @c ====================================================== Results of Tests. @node Results @chapter Results of Tests Once @command{configure} has determined whether a feature exists, what can it do to record that information? There are four sorts of things it can do: define a C preprocessor symbol, set a variable in the output files, save the result in a cache file for future @command{configure} runs, and print a message letting the user know the result of the test. @menu * Defining Symbols:: Defining C preprocessor symbols * Setting Output Variables:: Replacing variables in output files * Special Chars in Variables:: Characters to beware of in variables * Caching Results:: Speeding up subsequent @command{configure} runs * Printing Messages:: Notifying @command{configure} users @end menu @node Defining Symbols @section Defining C Preprocessor Symbols A common action to take in response to a feature test is to define a C preprocessor symbol indicating the results of the test. That is done by calling @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED}. By default, @code{AC_OUTPUT} places the symbols defined by these macros into the output variable @code{DEFS}, which contains an option @option{-D@var{symbol}=@var{value}} for each symbol defined. Unlike in Autoconf version 1, there is no variable @code{DEFS} defined while @command{configure} is running. To check whether Autoconf macros have already defined a certain C preprocessor symbol, test the value of the appropriate cache variable, as in this example: @example AC_CHECK_FUNC([vprintf], [AC_DEFINE([HAVE_VPRINTF], [1], [Define if vprintf exists.])]) if test "$ac_cv_func_vprintf" != yes; then AC_CHECK_FUNC([_doprnt], [AC_DEFINE([HAVE_DOPRNT], [1], [Define if _doprnt exists.])]) fi @end example If @code{AC_CONFIG_HEADERS} has been called, then instead of creating @code{DEFS}, @code{AC_OUTPUT} creates a header file by substituting the correct values into @code{#define} statements in a template file. @xref{Configuration Headers}, for more information about this kind of output. @defmac AC_DEFINE (@var{variable}, @var{value}, @ovar{description}) @defmacx AC_DEFINE (@var{variable}) @acindex{DEFINE} Define the C preprocessor variable @var{variable} to @var{value} (verbatim). @var{value} should not contain literal newlines, and if you are not using @code{AC_CONFIG_HEADERS} it should not contain any @samp{#} characters, as @command{make} tends to eat them. To use a shell variable, use @code{AC_DEFINE_UNQUOTED} instead. @var{description} is only useful if you are using @code{AC_CONFIG_HEADERS}. In this case, @var{description} is put into the generated @file{config.h.in} as the comment before the macro define. The following example defines the C preprocessor variable @code{EQUATION} to be the string constant @samp{"$a > $b"}: @example AC_DEFINE([EQUATION], ["$a > $b"], [Equation string.]) @end example If neither @var{value} nor @var{description} are given, then @var{value} defaults to 1 instead of to the empty string. This is for backwards compatibility with older versions of Autoconf, but this usage is obsolescent and may be withdrawn in future versions of Autoconf. If the @var{variable} is a literal string, it is passed to @code{m4_pattern_allow} (@pxref{Forbidden Patterns}). @end defmac @defmac AC_DEFINE_UNQUOTED (@var{variable}, @var{value}, @ovar{description}) @defmacx AC_DEFINE_UNQUOTED (@var{variable}) @acindex{DEFINE_UNQUOTED} Like @code{AC_DEFINE}, but three shell expansions are performed---once---on @var{variable} and @var{value}: variable expansion (@samp{$}), command substitution (@samp{`}), and backslash escaping (@samp{\}). Single and double quote characters in the value have no special meaning. Use this macro instead of @code{AC_DEFINE} when @var{variable} or @var{value} is a shell variable. Examples: @example AC_DEFINE_UNQUOTED([config_machfile], ["$machfile"], [Configuration machine file.]) AC_DEFINE_UNQUOTED([GETGROUPS_T], [$ac_cv_type_getgroups], [getgroups return type.]) AC_DEFINE_UNQUOTED([$ac_tr_hdr], [1], [Translated header name.]) @end example @end defmac Due to a syntactical bizarreness of the Bourne shell, do not use semicolons to separate @code{AC_DEFINE} or @code{AC_DEFINE_UNQUOTED} calls from other macro calls or shell code; that can cause syntax errors in the resulting @command{configure} script. Use either blanks or newlines. That is, do this: @example AC_CHECK_HEADER([elf.h], [AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"]) @end example @noindent or this: @example AC_CHECK_HEADER([elf.h], [AC_DEFINE([SVR4], [1], [System V Release 4]) LIBS="-lelf $LIBS"]) @end example @noindent instead of this: @example AC_CHECK_HEADER([elf.h], [AC_DEFINE([SVR4], [1], [System V Release 4]); LIBS="-lelf $LIBS"]) @end example @node Setting Output Variables @section Setting Output Variables @cindex Output variables Another way to record the results of tests is to set @dfn{output variables}, which are shell variables whose values are substituted into files that @command{configure} outputs. The two macros below create new output variables. @xref{Preset Output Variables}, for a list of output variables that are always available. @defmac AC_SUBST (@var{variable}, @ovar{value}) @acindex{SUBST} Create an output variable from a shell variable. Make @code{AC_OUTPUT} substitute the variable @var{variable} into output files (typically one or more makefiles). This means that @code{AC_OUTPUT} replaces instances of @samp{@@@var{variable}@@} in input files with the value that the shell variable @var{variable} has when @code{AC_OUTPUT} is called. The value can contain newlines. The substituted value is not rescanned for more output variables; occurrences of @samp{@@@var{variable}@@} in the value are inserted literally into the output file. (The algorithm uses the special marker @code{|#_!!_#|} internally, so the substituted value cannot contain @code{|#_!!_#|}.) If @var{value} is given, in addition assign it to @var{variable}. The string @var{variable} is passed to @code{m4_pattern_allow} (@pxref{Forbidden Patterns}). @end defmac @defmac AC_SUBST_FILE (@var{variable}) @acindex{SUBST_FILE} Another way to create an output variable from a shell variable. Make @code{AC_OUTPUT} insert (without substitutions) the contents of the file named by shell variable @var{variable} into output files. This means that @code{AC_OUTPUT} replaces instances of @samp{@@@var{variable}@@} in output files (such as @file{Makefile.in}) with the contents of the file that the shell variable @var{variable} names when @code{AC_OUTPUT} is called. Set the variable to @file{/dev/null} for cases that do not have a file to insert. This substitution occurs only when the @samp{@@@var{variable}@@} is on a line by itself, optionally surrounded by spaces and tabs. The substitution replaces the whole line, including the spaces, tabs, and the terminating newline. This macro is useful for inserting makefile fragments containing special dependencies or other @code{make} directives for particular host or target types into makefiles. For example, @file{configure.ac} could contain: @example AC_SUBST_FILE([host_frag]) host_frag=$srcdir/conf/sun4.mh @end example @noindent and then a @file{Makefile.in} could contain: @example @@host_frag@@ @end example The string @var{variable} is passed to @code{m4_pattern_allow} (@pxref{Forbidden Patterns}). @end defmac @cindex Precious Variable @cindex Variable, Precious Running @command{configure} in varying environments can be extremely dangerous. If for instance the user runs @samp{CC=bizarre-cc ./configure}, then the cache, @file{config.h}, and many other output files depend upon @command{bizarre-cc} being the C compiler. If for some reason the user runs @command{./configure} again, or if it is run via @samp{./config.status --recheck}, (@xref{Automatic Remaking}, and @pxref{config.status Invocation}), then the configuration can be inconsistent, composed of results depending upon two different compilers. Environment variables that affect this situation, such as @samp{CC} above, are called @dfn{precious variables}, and can be declared as such by @code{AC_ARG_VAR}. @defmac AC_ARG_VAR (@var{variable}, @var{description}) @acindex{ARG_VAR} Declare @var{variable} is a precious variable, and include its @var{description} in the variable section of @samp{./configure --help}. Being precious means that @itemize @minus @item @var{variable} is substituted via @code{AC_SUBST}. @item The value of @var{variable} when @command{configure} was launched is saved in the cache, including if it was not specified on the command line but via the environment. Indeed, while @command{configure} can notice the definition of @code{CC} in @samp{./configure CC=bizarre-cc}, it is impossible to notice it in @samp{CC=bizarre-cc ./configure}, which, unfortunately, is what most users do. We emphasize that it is the @emph{initial} value of @var{variable} which is saved, not that found during the execution of @command{configure}. Indeed, specifying @samp{./configure FOO=foo} and letting @samp{./configure} guess that @code{FOO} is @code{foo} can be two different things. @item @var{variable} is checked for consistency between two @command{configure} runs. For instance: @example $ @kbd{./configure --silent --config-cache} $ @kbd{CC=cc ./configure --silent --config-cache} configure: error: `CC' was not set in the previous run configure: error: changes in the environment can compromise \ the build configure: error: run `make distclean' and/or \ `rm config.cache' and start over @end example @noindent and similarly if the variable is unset, or if its content is changed. @item @var{variable} is kept during automatic reconfiguration (@pxref{config.status Invocation}) as if it had been passed as a command line argument, including when no cache is used: @example $ @kbd{CC=/usr/bin/cc ./configure undeclared_var=raboof --silent} $ @kbd{./config.status --recheck} running CONFIG_SHELL=/bin/sh /bin/sh ./configure undeclared_var=raboof \ CC=/usr/bin/cc --no-create --no-recursion @end example @end itemize @end defmac @node Special Chars in Variables @section Special Characters in Output Variables @cindex Output variables, special characters in Many output variables are intended to be evaluated both by @command{make} and by the shell. Some characters are expanded differently in these two contexts, so to avoid confusion these variables' values should not contain any of the following characters: @example " # $ & ' ( ) * ; < > ? [ \ ^ ` | @end example Also, these variables' values should neither contain newlines, nor start with @samp{~}, nor contain white space or @samp{:} immediately followed by @samp{~}. The values can contain nonempty sequences of white space characters like tabs and spaces, but each such sequence might arbitrarily be replaced by a single space during substitution. These restrictions apply both to the values that @command{configure} computes, and to the values set directly by the user. For example, the following invocations of @command{configure} are problematic, since they attempt to use special characters within @code{CPPFLAGS} and white space within @code{$(srcdir)}: @example CPPFLAGS='-DOUCH="&\"#$*?"' '../My Source/ouch-1.0/configure' '../My Source/ouch-1.0/configure' CPPFLAGS='-DOUCH="&\"#$*?"' @end example @node Caching Results @section Caching Results @cindex Cache To avoid checking for the same features repeatedly in various @command{configure} scripts (or in repeated runs of one script), @command{configure} can optionally save the results of many checks in a @dfn{cache file} (@pxref{Cache Files}). If a @command{configure} script runs with caching enabled and finds a cache file, it reads the results of previous runs from the cache and avoids rerunning those checks. As a result, @command{configure} can then run much faster than if it had to perform all of the checks every time. @defmac AC_CACHE_VAL (@var{cache-id}, @var{commands-to-set-it}) @acindex{CACHE_VAL} Ensure that the results of the check identified by @var{cache-id} are available. If the results of the check were in the cache file that was read, and @command{configure} was not given the @option{--quiet} or @option{--silent} option, print a message saying that the result was cached; otherwise, run the shell commands @var{commands-to-set-it}. If the shell commands are run to determine the value, the value is saved in the cache file just before @command{configure} creates its output files. @xref{Cache Variable Names}, for how to choose the name of the @var{cache-id} variable. The @var{commands-to-set-it} @emph{must have no side effects} except for setting the variable @var{cache-id}, see below. @end defmac @defmac AC_CACHE_CHECK (@var{message}, @var{cache-id}, @var{commands-to-set-it}) @acindex{CACHE_CHECK} A wrapper for @code{AC_CACHE_VAL} that takes care of printing the messages. This macro provides a convenient shorthand for the most common way to use these macros. It calls @code{AC_MSG_CHECKING} for @var{message}, then @code{AC_CACHE_VAL} with the @var{cache-id} and @var{commands} arguments, and @code{AC_MSG_RESULT} with @var{cache-id}. The @var{commands-to-set-it} @emph{must have no side effects} except for setting the variable @var{cache-id}, see below. @end defmac It is common to find buggy macros using @code{AC_CACHE_VAL} or @code{AC_CACHE_CHECK}, because people are tempted to call @code{AC_DEFINE} in the @var{commands-to-set-it}. Instead, the code that @emph{follows} the call to @code{AC_CACHE_VAL} should call @code{AC_DEFINE}, by examining the value of the cache variable. For instance, the following macro is broken: @example @group AC_DEFUN([AC_SHELL_TRUE], [AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works], [ac_cv_shell_true_works=no (true) 2>/dev/null && ac_cv_shell_true_works=yes if test "$ac_cv_shell_true_works" = yes; then AC_DEFINE([TRUE_WORKS], [1], [Define if `true(1)' works properly.]) fi]) ]) @end group @end example @noindent This fails if the cache is enabled: the second time this macro is run, @code{TRUE_WORKS} @emph{will not be defined}. The proper implementation is: @example @group AC_DEFUN([AC_SHELL_TRUE], [AC_CACHE_CHECK([whether true(1) works], [ac_cv_shell_true_works], [ac_cv_shell_true_works=no (true) 2>/dev/null && ac_cv_shell_true_works=yes]) if test "$ac_cv_shell_true_works" = yes; then AC_DEFINE([TRUE_WORKS], [1], [Define if `true(1)' works properly.]) fi ]) @end group @end example Also, @var{commands-to-set-it} should not print any messages, for example with @code{AC_MSG_CHECKING}; do that before calling @code{AC_CACHE_VAL}, so the messages are printed regardless of whether the results of the check are retrieved from the cache or determined by running the shell commands. @menu * Cache Variable Names:: Shell variables used in caches * Cache Files:: Files @command{configure} uses for caching * Cache Checkpointing:: Loading and saving the cache file @end menu @node Cache Variable Names @subsection Cache Variable Names @cindex Cache variable The names of cache variables should have the following format: @example @var{package-prefix}_cv_@var{value-type}_@var{specific-value}_@ovar{additional-options} @end example @noindent for example, @samp{ac_cv_header_stat_broken} or @samp{ac_cv_prog_gcc_traditional}. The parts of the variable name are: @table @asis @item @var{package-prefix} An abbreviation for your package or organization; the same prefix you begin local Autoconf macros with, except lowercase by convention. For cache values used by the distributed Autoconf macros, this value is @samp{ac}. @item @code{_cv_} Indicates that this shell variable is a cache value. This string @emph{must} be present in the variable name, including the leading underscore. @item @var{value-type} A convention for classifying cache values, to produce a rational naming system. The values used in Autoconf are listed in @ref{Macro Names}. @item @var{specific-value} Which member of the class of cache values this test applies to. For example, which function (@samp{alloca}), program (@samp{gcc}), or output variable (@samp{INSTALL}). @item @var{additional-options} Any particular behavior of the specific member that this test applies to. For example, @samp{broken} or @samp{set}. This part of the name may be omitted if it does not apply. @end table The values assigned to cache variables may not contain newlines. Usually, their values are Boolean (@samp{yes} or @samp{no}) or the names of files or functions; so this is not an important restriction. @node Cache Files @subsection Cache Files A cache file is a shell script that caches the results of configure tests run on one system so they can be shared between configure scripts and configure runs. It is not useful on other systems. If its contents are invalid for some reason, the user may delete or edit it. By default, @command{configure} uses no cache file, to avoid problems caused by accidental use of stale cache files. To enable caching, @command{configure} accepts @option{--config-cache} (or @option{-C}) to cache results in the file @file{config.cache}. Alternatively, @option{--cache-file=@var{file}} specifies that @var{file} be the cache file. The cache file is created if it does not exist already. When @command{configure} calls @command{configure} scripts in subdirectories, it uses the @option{--cache-file} argument so that they share the same cache. @xref{Subdirectories}, for information on configuring subdirectories with the @code{AC_CONFIG_SUBDIRS} macro. @file{config.status} only pays attention to the cache file if it is given the @option{--recheck} option, which makes it rerun @command{configure}. It is wrong to try to distribute cache files for particular system types. There is too much room for error in doing that, and too much administrative overhead in maintaining them. For any features that can't be guessed automatically, use the standard method of the canonical system type and linking files (@pxref{Manual Configuration}). The site initialization script can specify a site-wide cache file to use, instead of the usual per-program cache. In this case, the cache file gradually accumulates information whenever someone runs a new @command{configure} script. (Running @command{configure} merges the new cache results with the existing cache file.) This may cause problems, however, if the system configuration (e.g., the installed libraries or compilers) changes and the stale cache file is not deleted. @node Cache Checkpointing @subsection Cache Checkpointing If your configure script, or a macro called from @file{configure.ac}, happens to abort the configure process, it may be useful to checkpoint the cache a few times at key points using @code{AC_CACHE_SAVE}. Doing so reduces the amount of time it takes to rerun the configure script with (hopefully) the error that caused the previous abort corrected. @c FIXME: Do we really want to document this guy? @defmac AC_CACHE_LOAD @acindex{CACHE_LOAD} Loads values from existing cache file, or creates a new cache file if a cache file is not found. Called automatically from @code{AC_INIT}. @end defmac @defmac AC_CACHE_SAVE @acindex{CACHE_SAVE} Flushes all cached values to the cache file. Called automatically from @code{AC_OUTPUT}, but it can be quite useful to call @code{AC_CACHE_SAVE} at key points in @file{configure.ac}. @end defmac For instance: @example @r{ @dots{} AC_INIT, etc. @dots{}} @group # Checks for programs. AC_PROG_CC AC_PROG_AWK @r{ @dots{} more program checks @dots{}} AC_CACHE_SAVE @end group @group # Checks for libraries. AC_CHECK_LIB([nsl], [gethostbyname]) AC_CHECK_LIB([socket], [connect]) @r{ @dots{} more lib checks @dots{}} AC_CACHE_SAVE @end group @group # Might abort@dots{} AM_PATH_GTK([1.0.2], [], [AC_MSG_ERROR([GTK not in path])]) AM_PATH_GTKMM([0.9.5], [], [AC_MSG_ERROR([GTK not in path])]) @end group @r{ @dots{} AC_OUTPUT, etc. @dots{}} @end example @node Printing Messages @section Printing Messages @cindex Messages, from @command{configure} @command{configure} scripts need to give users running them several kinds of information. The following macros print messages in ways appropriate for each kind. The arguments to all of them get enclosed in shell double quotes, so the shell performs variable and back-quote substitution on them. These macros are all wrappers around the @command{echo} shell command. They direct output to the appropriate file descriptor (@pxref{File Descriptor Macros}). @command{configure} scripts should rarely need to run @command{echo} directly to print messages for the user. Using these macros makes it easy to change how and when each kind of message is printed; such changes need only be made to the macro definitions and all the callers change automatically. To diagnose static issues, i.e., when @command{autoconf} is run, see @ref{Reporting Messages}. @defmac AC_MSG_CHECKING (@var{feature-description}) @acindex{MSG_CHECKING} Notify the user that @command{configure} is checking for a particular feature. This macro prints a message that starts with @samp{checking } and ends with @samp{...} and no newline. It must be followed by a call to @code{AC_MSG_RESULT} to print the result of the check and the newline. The @var{feature-description} should be something like @samp{whether the Fortran compiler accepts C++ comments} or @samp{for c89}. This macro prints nothing if @command{configure} is run with the @option{--quiet} or @option{--silent} option. @end defmac @defmac AC_MSG_RESULT (@var{result-description}) @acindex{MSG_RESULT} Notify the user of the results of a check. @var{result-description} is almost always the value of the cache variable for the check, typically @samp{yes}, @samp{no}, or a file name. This macro should follow a call to @code{AC_MSG_CHECKING}, and the @var{result-description} should be the completion of the message printed by the call to @code{AC_MSG_CHECKING}. This macro prints nothing if @command{configure} is run with the @option{--quiet} or @option{--silent} option. @end defmac @defmac AC_MSG_NOTICE (@var{message}) @acindex{MSG_NOTICE} Deliver the @var{message} to the user. It is useful mainly to print a general description of the overall purpose of a group of feature checks, e.g., @example AC_MSG_NOTICE([checking if stack overflow is detectable]) @end example This macro prints nothing if @command{configure} is run with the @option{--quiet} or @option{--silent} option. @end defmac @defmac AC_MSG_ERROR (@var{error-description}, @ovar{exit-status}) @acindex{MSG_ERROR} Notify the user of an error that prevents @command{configure} from completing. This macro prints an error message to the standard error output and exits @command{configure} with @var{exit-status} (1 by default). @var{error-description} should be something like @samp{invalid value $HOME for \$HOME}. The @var{error-description} should start with a lower-case letter, and ``cannot'' is preferred to ``can't''. @end defmac @defmac AC_MSG_FAILURE (@var{error-description}, @ovar{exit-status}) @acindex{MSG_FAILURE} This @code{AC_MSG_ERROR} wrapper notifies the user of an error that prevents @command{configure} from completing @emph{and} that additional details are provided in @file{config.log}. This is typically used when abnormal results are found during a compilation. @end defmac @defmac AC_MSG_WARN (@var{problem-description}) @acindex{MSG_WARN} Notify the @command{configure} user of a possible problem. This macro prints the message to the standard error output; @command{configure} continues running afterward, so macros that call @code{AC_MSG_WARN} should provide a default (back-up) behavior for the situations they warn about. @var{problem-description} should be something like @samp{ln -s seems to make hard links}. @end defmac @c ====================================================== Programming in M4. @node Programming in M4 @chapter Programming in M4 @cindex M4 Autoconf is written on top of two layers: @dfn{M4sugar}, which provides convenient macros for pure M4 programming, and @dfn{M4sh}, which provides macros dedicated to shell script generation. As of this version of Autoconf, these two layers are still experimental, and their interface might change in the future. As a matter of fact, @emph{anything that is not documented must not be used}. @menu * M4 Quotation:: Protecting macros from unwanted expansion * Using autom4te:: The Autoconf executables backbone * Programming in M4sugar:: Convenient pure M4 macros * Programming in M4sh:: Common shell Constructs * File Descriptor Macros:: File descriptor macros for input and output @end menu @node M4 Quotation @section M4 Quotation @cindex M4 quotation @cindex quotation @c FIXME: Grmph, yet another quoting myth: quotation has *never* @c prevented `expansion' of $1. Unless it refers to the expansion @c of the value of $1? Anyway, we need a rewrite here@enddots{} The most common problem with existing macros is an improper quotation. This section, which users of Autoconf can skip, but which macro writers @emph{must} read, first justifies the quotation scheme that was chosen for Autoconf and then ends with a rule of thumb. Understanding the former helps one to follow the latter. @menu * Active Characters:: Characters that change the behavior of M4 * One Macro Call:: Quotation and one macro call * Quotation and Nested Macros:: Macros calling macros * Changequote is Evil:: Worse than INTERCAL: M4 + changequote * Quadrigraphs:: Another way to escape special characters * Quotation Rule Of Thumb:: One parenthesis, one quote @end menu @node Active Characters @subsection Active Characters To fully understand where proper quotation is important, you first need to know what the special characters are in Autoconf: @samp{#} introduces a comment inside which no macro expansion is performed, @samp{,} separates arguments, @samp{[} and @samp{]} are the quotes themselves, and finally @samp{(} and @samp{)} (which M4 tries to match by pairs). In order to understand the delicate case of macro calls, we first have to present some obvious failures. Below they are ``obvious-ified'', but when you find them in real life, they are usually in disguise. Comments, introduced by a hash and running up to the newline, are opaque tokens to the top level: active characters are turned off, and there is no macro expansion: @example # define([def], ine) @result{}# define([def], ine) @end example Each time there can be a macro expansion, there is a quotation expansion, i.e., one level of quotes is stripped: @example int tab[10]; @result{}int tab10; [int tab[10];] @result{}int tab[10]; @end example Without this in mind, the reader might try hopelessly to use her macro @code{array}: @example define([array], [int tab[10];]) array @result{}int tab10; [array] @result{}array @end example @noindent How can you correctly output the intended results@footnote{Using @code{defn}.}? @node One Macro Call @subsection One Macro Call Let's proceed on the interaction between active characters and macros with this small macro, which just returns its first argument: @example define([car], [$1]) @end example @noindent The two pairs of quotes above are not part of the arguments of @code{define}; rather, they are understood by the top level when it tries to find the arguments of @code{define}. Therefore, assuming @code{car} is not already defined, it is equivalent to write: @example define(car, $1) @end example @noindent But, while it is acceptable for a @file{configure.ac} to avoid unnecessary quotes, it is bad practice for Autoconf macros which must both be more robust and also advocate perfect style. At the top level, there are only two possibilities: either you quote or you don't: @example car(foo, bar, baz) @result{}foo [car(foo, bar, baz)] @result{}car(foo, bar, baz) @end example Let's pay attention to the special characters: @example car(#) @error{}EOF in argument list @end example The closing parenthesis is hidden in the comment; with a hypothetical quoting, the top level understood it this way: @example car([#)] @end example @noindent Proper quotation, of course, fixes the problem: @example car([#]) @result{}# @end example Here are more examples: @example car(foo, bar) @result{}foo car([foo, bar]) @result{}foo, bar car((foo, bar)) @result{}(foo, bar) car([(foo], [bar)]) @result{}(foo define([a], [b]) @result{} car(a) @result{}b car([a]) @result{}b car([[a]]) @result{}a car([[[a]]]) @result{}[a] @end example With this in mind, we can explore the cases where macros invoke macros@enddots{} @node Quotation and Nested Macros @subsection Quotation and Nested Macros The examples below use the following macros: @example define([car], [$1]) define([active], [ACT, IVE]) define([array], [int tab[10]]) @end example Each additional embedded macro call introduces other possible interesting quotations: @example car(active) @result{}ACT car([active]) @result{}ACT, IVE car([[active]]) @result{}active @end example In the first case, the top level looks for the arguments of @code{car}, and finds @samp{active}. Because M4 evaluates its arguments before applying the macro, @samp{active} is expanded, which results in: @example car(ACT, IVE) @result{}ACT @end example @noindent In the second case, the top level gives @samp{active} as first and only argument of @code{car}, which results in: @example active @result{}ACT, IVE @end example @noindent i.e., the argument is evaluated @emph{after} the macro that invokes it. In the third case, @code{car} receives @samp{[active]}, which results in: @example [active] @result{}active @end example @noindent exactly as we already saw above. The example above, applied to a more realistic example, gives: @example car(int tab[10];) @result{}int tab10; car([int tab[10];]) @result{}int tab10; car([[int tab[10];]]) @result{}int tab[10]; @end example @noindent Huh? The first case is easily understood, but why is the second wrong, and the third right? To understand that, you must know that after M4 expands a macro, the resulting text is immediately subjected to macro expansion and quote removal. This means that the quote removal occurs twice---first before the argument is passed to the @code{car} macro, and second after the @code{car} macro expands to the first argument. As the author of the Autoconf macro @code{car}, you then consider it to be incorrect that your users have to double-quote the arguments of @code{car}, so you ``fix'' your macro. Let's call it @code{qar} for quoted car: @example define([qar], [[$1]]) @end example @noindent and check that @code{qar} is properly fixed: @example qar([int tab[10];]) @result{}int tab[10]; @end example @noindent Ahhh! That's much better. But note what you've done: now that the arguments are literal strings, if the user wants to use the results of expansions as arguments, she has to use an @emph{unquoted} macro call: @example qar(active) @result{}ACT @end example @noindent where she wanted to reproduce what she used to do with @code{car}: @example car([active]) @result{}ACT, IVE @end example @noindent Worse yet: she wants to use a macro that produces a set of @code{cpp} macros: @example define([my_includes], [#include ]) car([my_includes]) @result{}#include qar(my_includes) @error{}EOF in argument list @end example This macro, @code{qar}, because it double quotes its arguments, forces its users to leave their macro calls unquoted, which is dangerous. Commas and other active symbols are interpreted by M4 before they are given to the macro, often not in the way the users expect. Also, because @code{qar} behaves differently from the other macros, it's an exception that should be avoided in Autoconf. @node Changequote is Evil @subsection @code{changequote} is Evil @cindex @code{changequote} The temptation is often high to bypass proper quotation, in particular when it's late at night. Then, many experienced Autoconf hackers finally surrender to the dark side of the force and use the ultimate weapon: @code{changequote}. The M4 builtin @code{changequote} belongs to a set of primitives that allow one to adjust the syntax of the language to adjust it to one's needs. For instance, by default M4 uses @samp{`} and @samp{'} as quotes, but in the context of shell programming (and actually of most programming languages), that's about the worst choice one can make: because of strings and back-quoted expressions in shell code (such as @samp{'this'} and @samp{`that`}), because of literal characters in usual programming languages (as in @samp{'0'}), there are many unbalanced @samp{`} and @samp{'}. Proper M4 quotation then becomes a nightmare, if not impossible. In order to make M4 useful in such a context, its designers have equipped it with @code{changequote}, which makes it possible to choose another pair of quotes. M4sugar, M4sh, Autoconf, and Autotest all have chosen to use @samp{[} and @samp{]}. Not especially because they are unlikely characters, but @emph{because they are characters unlikely to be unbalanced}. There are other magic primitives, such as @code{changecom} to specify what syntactic forms are comments (it is common to see @samp{changecom()} when M4 is used to produce HTML pages), @code{changeword} and @code{changesyntax} to change other syntactic details (such as the character to denote the @var{n}th argument, @samp{$} by default, the parenthesis around arguments, etc.). These primitives are really meant to make M4 more useful for specific domains: they should be considered like command line options: @option{--quotes}, @option{--comments}, @option{--words}, and @option{--syntax}. Nevertheless, they are implemented as M4 builtins, as it makes M4 libraries self contained (no need for additional options). There lies the problem@enddots{} @sp 1 The problem is that it is then tempting to use them in the middle of an M4 script, as opposed to its initialization. This, if not carefully thought out, can lead to disastrous effects: @emph{you are changing the language in the middle of the execution}. Changing and restoring the syntax is often not enough: if you happened to invoke macros in between, these macros are lost, as the current syntax is probably not the one they were implemented with. @c FIXME: I've been looking for a short, real case example, but I @c lost them all :( @node Quadrigraphs @subsection Quadrigraphs @cindex quadrigraphs @cindex @samp{@@S|@@} @cindex @samp{@@&t@@} @c Info cannot handle `:' in index entries. @c @cindex @samp{@@<:@@} @c @cindex @samp{@@:>@@} @c @cindex @samp{@@%:@@} When writing an Autoconf macro you may occasionally need to generate special characters that are difficult to express with the standard Autoconf quoting rules. For example, you may need to output the regular expression @samp{[^[]}, which matches any character other than @samp{[}. This expression contains unbalanced brackets so it cannot be put easily into an M4 macro. You can work around this problem by using one of the following @dfn{quadrigraphs}: @table @samp @item @@<:@@ @samp{[} @item @@:>@@ @samp{]} @item @@S|@@ @samp{$} @item @@%:@@ @samp{#} @item @@&t@@ Expands to nothing. @end table Quadrigraphs are replaced at a late stage of the translation process, after @command{m4} is run, so they do not get in the way of M4 quoting. For example, the string @samp{^@@<:@@}, independently of its quotation, appears as @samp{^[} in the output. The empty quadrigraph can be used: @itemize @minus @item to mark trailing spaces explicitly Trailing spaces are smashed by @command{autom4te}. This is a feature. @item to produce other quadrigraphs For instance @samp{@@<@@&t@@:@@} produces @samp{@@<:@@}. @item to escape @emph{occurrences} of forbidden patterns For instance you might want to mention @code{AC_FOO} in a comment, while still being sure that @command{autom4te} still catches unexpanded @samp{AC_*}. Then write @samp{AC@@&t@@_FOO}. @end itemize The name @samp{@@&t@@} was suggested by Paul Eggert: @quotation I should give some credit to the @samp{@@&t@@} pun. The @samp{&} is my own invention, but the @samp{t} came from the source code of the @sc{algol68c} compiler, written by Steve Bourne (of Bourne shell fame), and which used @samp{mt} to denote the empty string. In C, it would have looked like something like: @example char const mt[] = ""; @end example @noindent but of course the source code was written in Algol 68. I don't know where he got @samp{mt} from: it could have been his own invention, and I suppose it could have been a common pun around the Cambridge University computer lab at the time. @end quotation @node Quotation Rule Of Thumb @subsection Quotation Rule Of Thumb To conclude, the quotation rule of thumb is: @center @emph{One pair of quotes per pair of parentheses.} Never over-quote, never under-quote, in particular in the definition of macros. In the few places where the macros need to use brackets (usually in C program text or regular expressions), properly quote @emph{the arguments}! It is common to read Autoconf programs with snippets like: @example AC_TRY_LINK( changequote(<<, >>)dnl <<#include #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif>>, changequote([, ])dnl [atoi (*tzname);], ac_cv_var_tzname=yes, ac_cv_var_tzname=no) @end example @noindent which is incredibly useless since @code{AC_TRY_LINK} is @emph{already} double quoting, so you just need: @example AC_TRY_LINK( [#include #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif], [atoi (*tzname);], [ac_cv_var_tzname=yes], [ac_cv_var_tzname=no]) @end example @noindent The M4-fluent reader might note that these two examples are rigorously equivalent, since M4 swallows both the @samp{changequote(<<, >>)} and @samp{<<} @samp{>>} when it @dfn{collects} the arguments: these quotes are not part of the arguments! Simplified, the example above is just doing this: @example changequote(<<, >>)dnl <<[]>> changequote([, ])dnl @end example @noindent instead of simply: @example [[]] @end example With macros that do not double quote their arguments (which is the rule), double-quote the (risky) literals: @example AC_LINK_IFELSE([AC_LANG_PROGRAM( [[#include #ifndef tzname /* For SGI. */ extern char *tzname[]; /* RS6000 and others reject char **tzname. */ #endif]], [atoi (*tzname);])], [ac_cv_var_tzname=yes], [ac_cv_var_tzname=no]) @end example Please note that the macro @code{AC_TRY_LINK} is obsolete, so you really should be using @code{AC_LINK_IFELSE} instead. @xref{Quadrigraphs}, for what to do if you run into a hopeless case where quoting does not suffice. When you create a @command{configure} script using newly written macros, examine it carefully to check whether you need to add more quotes in your macros. If one or more words have disappeared in the M4 output, you need more quotes. When in doubt, quote. However, it's also possible to put on too many layers of quotes. If this happens, the resulting @command{configure} script may contain unexpanded macros. The @command{autoconf} program checks for this problem by looking for the string @samp{AC_} in @file{configure}. However, this heuristic does not work in general: for example, it does not catch overquoting in @code{AC_DEFINE} descriptions. @c ---------------------------------------- Using autom4te @node Using autom4te @section Using @command{autom4te} The Autoconf suite, including M4sugar, M4sh, and Autotest, in addition to Autoconf per se, heavily rely on M4. All these different uses revealed common needs factored into a layer over M4: @command{autom4te}@footnote{ @c Yet another great name from Lars J. Aas. @c }. @command{autom4te} is a preprocessor that is like @command{m4}. It supports M4 extensions designed for use in tools like Autoconf. @menu * autom4te Invocation:: A @acronym{GNU} M4 wrapper * Customizing autom4te:: Customizing the Autoconf package @end menu @node autom4te Invocation @subsection Invoking @command{autom4te} The command line arguments are modeled after M4's: @example autom4te @var{options} @var{files} @end example @noindent @evindex M4 where the @var{files} are directly passed to @command{m4}. By default, @acronym{GNU} M4 is found during configuration, but the environment variable @env{M4} can be set to tell @command{autom4te} where to look. In addition to the regular expansion, it handles the replacement of the quadrigraphs (@pxref{Quadrigraphs}), and of @samp{__oline__}, the current line in the output. It supports an extended syntax for the @var{files}: @table @file @item @var{file}.m4f This file is an M4 frozen file. Note that @emph{all the previous files are ignored}. See the option @option{--melt} for the rationale. @item @var{file}? If found in the library path, the @var{file} is included for expansion, otherwise it is ignored instead of triggering a failure. @end table @sp 1 Of course, it supports the Autoconf common subset of options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Report processing steps. @item --debug @itemx -d Don't remove the temporary files and be even more verbose. @item --include=@var{dir} @itemx -I @var{dir} Also look for input files in @var{dir}. Multiple invocations accumulate. @item --output=@var{file} @itemx -o @var{file} Save output (script or trace) to @var{file}. The file @option{-} stands for the standard output. @end table @sp 1 As an extension of @command{m4}, it includes the following options: @table @option @item --warnings=@var{category} @itemx -W @var{category} @evindex WARNINGS @c FIXME: Point to the M4sugar macros, not Autoconf's. Report the warnings related to @var{category} (which can actually be a comma separated list). @xref{Reporting Messages}, macro @code{AC_DIAGNOSE}, for a comprehensive list of categories. Special values include: @table @samp @item all report all the warnings @item none report none @item error treats warnings as errors @item no-@var{category} disable warnings falling into @var{category} @end table Warnings about @samp{syntax} are enabled by default, and the environment variable @env{WARNINGS}, a comma separated list of categories, is honored. @samp{autom4te -W @var{category}} actually behaves as if you had run: @example autom4te --warnings=syntax,$WARNINGS,@var{category} @end example @noindent For example, if you want to disable defaults and @env{WARNINGS} of @command{autom4te}, but enable the warnings about obsolete constructs, you would use @option{-W none,obsolete}. @cindex Back trace @cindex Macro invocation stack @command{autom4te} displays a back trace for errors, but not for warnings; if you want them, just pass @option{-W error}. @item --melt @itemx -M Do not use frozen files. Any argument @code{@var{file}.m4f} is replaced by @code{@var{file}.m4}. This helps tracing the macros which are executed only when the files are frozen, typically @code{m4_define}. For instance, running: @example autom4te --melt 1.m4 2.m4f 3.m4 4.m4f input.m4 @end example @noindent is roughly equivalent to running: @example m4 1.m4 2.m4 3.m4 4.m4 input.m4 @end example @noindent while @example autom4te 1.m4 2.m4f 3.m4 4.m4f input.m4 @end example @noindent is equivalent to: @example m4 --reload-state=4.m4f input.m4 @end example @item --freeze @itemx -f Produce a frozen state file. @command{autom4te} freezing is stricter than M4's: it must produce no warnings, and no output other than empty lines (a line with white space is @emph{not} empty) and comments (starting with @samp{#}). Unlike @command{m4}'s similarly-named option, this option takes no argument: @example autom4te 1.m4 2.m4 3.m4 --freeze --output=3.m4f @end example @noindent corresponds to @example m4 1.m4 2.m4 3.m4 --freeze-state=3.m4f @end example @item --mode=@var{octal-mode} @itemx -m @var{octal-mode} Set the mode of the non-traces output to @var{octal-mode}; by default @samp{0666}. @end table @sp 1 @cindex @file{autom4te.cache} As another additional feature over @command{m4}, @command{autom4te} caches its results. @acronym{GNU} M4 is able to produce a regular output and traces at the same time. Traces are heavily used in the @acronym{GNU} Build System: @command{autoheader} uses them to build @file{config.h.in}, @command{autoreconf} to determine what @acronym{GNU} Build System components are used, @command{automake} to ``parse'' @file{configure.ac} etc. To avoid recomputation, traces are cached while performing regular expansion, and conversely. This cache is (actually, the caches are) stored in the directory @file{autom4te.cache}. @emph{It can safely be removed} at any moment (especially if for some reason @command{autom4te} considers it is trashed). @table @option @item --cache=@var{directory} @itemx -C @var{directory} Specify the name of the directory where the result should be cached. Passing an empty value disables caching. Be sure to pass a relative file name, as for the time being, global caches are not supported. @item --no-cache Don't cache the results. @item --force @itemx -f If a cache is used, consider it obsolete (but update it anyway). @end table @sp 1 Because traces are so important to the @acronym{GNU} Build System, @command{autom4te} provides high level tracing features as compared to M4, and helps exploiting the cache: @table @option @item --trace=@var{macro}[:@var{format}] @itemx -t @var{macro}[:@var{format}] Trace the invocations of @var{macro} according to the @var{format}. Multiple @option{--trace} arguments can be used to list several macros. Multiple @option{--trace} arguments for a single macro are not cumulative; instead, you should just make @var{format} as long as needed. The @var{format} is a regular string, with newlines if desired, and several special escape codes. It defaults to @samp{$f:$l:$n:$%}. It can use the following special escapes: @table @samp @item $$ The character @samp{$}. @item $f The file name from which @var{macro} is called. @item $l The line number from which @var{macro} is called. @item $d The depth of the @var{macro} call. This is an M4 technical detail that you probably don't want to know about. @item $n The name of the @var{macro}. @item $@var{num} The @var{num}th argument of the call to @var{macro}. @item $@@ @itemx $@var{sep}@@ @itemx $@{@var{separator}@}@@ All the arguments passed to @var{macro}, separated by the character @var{sep} or the string @var{separator} (@samp{,} by default). Each argument is quoted, i.e., enclosed in a pair of square brackets. @item $* @itemx $@var{sep}* @itemx $@{@var{separator}@}* As above, but the arguments are not quoted. @item $% @itemx $@var{sep}% @itemx $@{@var{separator}@}% As above, but the arguments are not quoted, all new line characters in the arguments are smashed, and the default separator is @samp{:}. The escape @samp{$%} produces single-line trace outputs (unless you put newlines in the @samp{separator}), while @samp{$@@} and @samp{$*} do not. @end table @xref{autoconf Invocation}, for examples of trace uses. @item --preselect=@var{macro} @itemx -p @var{macro} Cache the traces of @var{macro}, but do not enable traces. This is especially important to save CPU cycles in the future. For instance, when invoked, @command{autoconf} preselects all the macros that @command{autoheader}, @command{automake}, @command{autoreconf}, etc., trace, so that running @command{m4} is not needed to trace them: the cache suffices. This results in a huge speed-up. @end table @sp 1 @cindex Autom4te Library Finally, @command{autom4te} introduces the concept of @dfn{Autom4te libraries}. They consists in a powerful yet extremely simple feature: sets of combined command line arguments: @table @option @item --language=@var{language} @itemx -l @var{language} Use the @var{language} Autom4te library. Current languages include: @table @code @item M4sugar create M4sugar output. @item M4sh create M4sh executable shell scripts. @item Autotest create Autotest executable test suites. @item Autoconf-without-aclocal-m4 create Autoconf executable configure scripts without reading @file{aclocal.m4}. @item Autoconf create Autoconf executable configure scripts. This language inherits all the characteristics of @code{Autoconf-without-aclocal-m4} and additionally reads @file{aclocal.m4}. @end table @item --prepend-include=@var{dir} @item -B @var{dir} Prepend directory @var{dir} to the search path. This is used to include the language-specific files before any third-party macros. @end table @cindex @file{autom4te.cfg} As an example, if Autoconf is installed in its default location, @file{/usr/local}, the command @samp{autom4te -l m4sugar foo.m4} is strictly equivalent to the command: @example autom4te --prepend-include /usr/local/share/autoconf \ m4sugar/m4sugar.m4f --warnings syntax foo.m4 @end example @noindent Recursive expansion applies here: the command @samp{autom4te -l m4sh foo.m4} is the same as @samp{autom4te --language M4sugar m4sugar/m4sh.m4f foo.m4}, i.e.: @example autom4te --prepend-include /usr/local/share/autoconf \ m4sugar/m4sugar.m4f m4sugar/m4sh.m4f --mode 777 foo.m4 @end example @noindent The definition of the languages is stored in @file{autom4te.cfg}. @node Customizing autom4te @subsection Customizing @command{autom4te} One can customize @command{autom4te} via @file{~/.autom4te.cfg} (i.e., as found in the user home directory), and @file{./.autom4te.cfg} (i.e., as found in the directory from which @command{autom4te} is run). The order is first reading @file{autom4te.cfg}, then @file{~/.autom4te.cfg}, then @file{./.autom4te.cfg}, and finally the command line arguments. In these text files, comments are introduced with @code{#}, and empty lines are ignored. Customization is performed on a per-language basis, wrapped in between a @samp{begin-language: "@var{language}"}, @samp{end-language: "@var{language}"} pair. Customizing a language stands for appending options (@pxref{autom4te Invocation}) to the current definition of the language. Options, and more generally arguments, are introduced by @samp{args: @var{arguments}}. You may use the traditional shell syntax to quote the @var{arguments}. As an example, to disable Autoconf caches (@file{autom4te.cache}) globally, include the following lines in @file{~/.autom4te.cfg}: @verbatim ## ------------------ ## ## User Preferences. ## ## ------------------ ## begin-language: "Autoconf-without-aclocal-m4" args: --no-cache end-language: "Autoconf-without-aclocal-m4" @end verbatim @node Programming in M4sugar @section Programming in M4sugar @cindex M4sugar M4 by itself provides only a small, but sufficient, set of all-purpose macros. M4sugar introduces additional generic macros. Its name was coined by Lars J. Aas: ``Readability And Greater Understanding Stands 4 M4sugar''. @menu * Redefined M4 Macros:: M4 builtins changed in M4sugar * Looping constructs:: Iteration in M4 * Evaluation Macros:: More quotation and evaluation control * Text processing Macros:: String manipulation in M4 * Forbidden Patterns:: Catching unexpanded macros @end menu @node Redefined M4 Macros @subsection Redefined M4 Macros @msindex{builtin} @msindex{decr} @msindex{define} @msindex{dumpdef} @msindex{errprint} @msindex{esyscmd} @msindex{eval} @msindex{format} @msindex{ifdef} @msindex{incr} @msindex{index} @msindex{indir} @msindex{len} @msindex{pushdef} @msindex{shift} @msindex{substr} @msindex{syscmd} @msindex{sysval} @msindex{translit} @msindex{undefine} With a few exceptions, all the M4 native macros are moved in the @samp{m4_} pseudo-namespace, e.g., M4sugar renames @code{define} as @code{m4_define} etc. Some M4 macros are redefined, and are slightly incompatible with their native equivalent. @defmac dnl @msindex{dnl} This macro kept its original name: no @code{m4_dnl} is defined. @end defmac @defmac m4_defn (@var{macro}) @msindex{defn} Unlike the M4 builtin, this macro fails if @var{macro} is not defined. See @code{m4_undefine}. @end defmac @defmac m4_exit (@var{exit-status}) @msindex{exit} This macro corresponds to @code{m4exit}. @end defmac @defmac m4_if (@var{comment}) @defmacx m4_if (@var{string-1}, @var{string-2}, @var{equal}, @ovar{not-equal}) @defmacx m4_if (@var{string-1}, @var{string-2}, @var{equal}, @dots{}) @msindex{if} This macro corresponds to @code{ifelse}. @end defmac @defmac m4_include (@var{file}) @defmacx m4_sinclude (@var{file}) @msindex{include} @msindex{sinclude} Like the M4 builtins, but warn against multiple inclusions of @var{file}. @end defmac @defmac m4_bpatsubst (@var{string}, @var{regexp}, @ovar{replacement}) @msindex{bpatsubst} This macro corresponds to @code{patsubst}. The name @code{m4_patsubst} is kept for future versions of M4sh, on top of @acronym{GNU} M4 which will provide extended regular expression syntax via @code{epatsubst}. @end defmac @defmac m4_popdef (@var{macro}) @msindex{popdef} Unlike the M4 builtin, this macro fails if @var{macro} is not defined. See @code{m4_undefine}. @end defmac @defmac m4_bregexp (@var{string}, @var{regexp}, @ovar{replacement}) @msindex{bregexp} This macro corresponds to @code{regexp}. The name @code{m4_regexp} is kept for future versions of M4sh, on top of @acronym{GNU} M4 which will provide extended regular expression syntax via @code{eregexp}. @end defmac @defmac m4_wrap (@var{text}) @msindex{wrap} This macro corresponds to @code{m4wrap}. Posix requires arguments of multiple @code{m4wrap} calls to be reprocessed at @acronym{EOF} in the same order as the original calls. @acronym{GNU} M4 versions through 1.4.x, however, reprocess them in reverse order. Your code should not depend on the order. Also, Posix requires @code{m4wrap} to ignore its second and succeeding arguments, but @acronym{GNU} M4 versions through 1.4.x concatenate the arguments with intervening spaces. Your code should not pass more than one argument. You are encouraged to end @var{text} with @samp{[]}, to avoid unexpected token pasting between consecutive invocations of @code{m4_wrap}, as in: @example m4_define([foo], [bar]) m4_define([foofoo], [OUCH]) m4_wrap([foo]) m4_wrap([foo]) @result{}OUCH @end example @end defmac @defmac m4_undefine (@var{macro}) @msindex{undefine} Unlike the M4 builtin, this macro fails if @var{macro} is not defined. Use @example m4_ifdef([@var{macro}], [m4_undefine([@var{macro}])]) @end example @noindent to recover the behavior of the builtin. @end defmac @defmac m4_maketemp (@var{template}) @defmacx m4_mkstemp (@var{template}) @msindex{maketemp} @msindex{mkstemp} Posix requires @code{maketemp} to replace the trailing @samp{X} characters in @var{template} with the process id, without regards to the existence of a file by that name, but this a security hole. When this was pointed out to the Posix folks, they agreed to invent a new macro @code{mkstemp} that always creates a uniquely named file, but not all versions of @acronym{GNU} M4 support the new macro. In M4sugar, @code{m4_maketemp} and @code{m4_mkstemp} are synonyms for each other, and both have the secure semantics regardless of which macro the underlying M4 provides. @end defmac @node Looping constructs @subsection Looping constructs The following macros implement loops in M4. @defmac m4_for (@var{var}, @var{first}, @var{last}, @ovar{step}, @var{expression}) @msindex{for} Loop over the numeric values between @var{first} and @var{last} including bounds by increments of @var{step}. For each iteration, expand @var{expression} with the numeric value assigned to @var{var}. If @var{step} is omitted, it defaults to @samp{1} or @samp{-1} depending on the order of the limits. If given, @var{step} has to match this order. @end defmac @defmac m4_foreach (@var{var}, @var{list}, @var{expression}) @msindex{foreach} Loop over the comma-separated M4 list @var{list}, assigning each value to @var{var}, and expand @var{expression}. The following example outputs two lines: @example m4_foreach([myvar], [[foo], [bar, baz]], [echo myvar ]) @end example @end defmac @defmac m4_foreach_w (@var{var}, @var{list}, @var{expression}) @msindex{foreach_w} Loop over the white-space-separated list @var{list}, assigning each value to @var{var}, and expand @var{expression}. The deprecated macro @code{AC_FOREACH} is an alias of @code{m4_foreach_w}. @end defmac @node Evaluation Macros @subsection Evaluation Macros The following macros give some control over the order of the evaluation by adding or removing levels of quotes. They are meant for hard-core M4 programmers. @defmac m4_dquote (@var{arg1}, @dots{}) @msindex{dquote} Return the arguments as a quoted list of quoted arguments. @end defmac @defmac m4_quote (@var{arg1}, @dots{}) @msindex{quote} Return the arguments as a single entity, i.e., wrap them into a pair of quotes. @end defmac The following example aims at emphasizing the difference between (i), not using these macros, (ii), using @code{m4_quote}, and (iii), using @code{m4_dquote}. @example $ @kbd{cat example.m4} # Overquote, so that quotes are visible. m4_define([show], [$[]1 = [$1], $[]@@ = [$@@]]) m4_define([mkargs], [1, 2, 3]) m4_define([arg1], [[$1]]) m4_divert(0)dnl show(a, b) show(m4_quote(a, b)) show(m4_dquote(a, b)) arg1(mkargs) arg1([mkargs]) arg1(m4_defn([mkargs])) arg1(m4_quote(mkargs)) arg1(m4_dquote(mkargs)) $ @kbd{autom4te -l m4sugar example.m4} $1 = a, $@@ = [a],[b] $1 = a,b, $@@ = [a,b] $1 = [a],[b], $@@ = [[a],[b]] 1 mkargs 1, 2, 3 1,2,3 [1],[2],[3] @end example @node Text processing Macros @subsection Text processing Macros The following macros may be used to manipulate strings in M4. They are not intended for casual use. @defmac m4_re_escape (@var{string}) @msindex{re_escape} Backslash-escape all characters in @var{string} that are active in regexps. @end defmac @defmac m4_tolower (@var{string}) @defmacx m4_toupper (@var{string}) @msindex{tolower} @msindex{toupper} Return @var{string} with letters converted to upper or lower case, respectively. @end defmac @defmac m4_split (@var{string}, @ovar{regexp}) @msindex{split} Split @var{string} into an M4 list of elements quoted by @samp{[} and @samp{]}, while keeping white space at the beginning and at the end. If @var{regexp} is given, use it instead of @samp{[\t ]+} for splitting. If @var{string} is empty, the result is an empty list. @end defmac @defmac m4_normalize (@var{string}) @msindex{normalize} Remove leading and trailing spaces and tabs, sequences of backslash-then-newline, and replace multiple spaces and tabs with a single space. @end defmac @defmac m4_append (@var{macro-name}, @var{string}, @ovar{separator}) @defmacx m4_append_uniq (@var{macro-name}, @var{string}, @ovar{separator}) @msindex{append} @msindex{append_uniq} Redefine @var{macro-name} to its former contents with @var{separator} and @var{string} added at the end. If @var{macro-name} was undefined before (but not if it was defined but empty), then no @var{separator} is added. @code{m4_append} can be used to grow strings, and @code{m4_append_uniq} to grow strings without duplicating substrings. @end defmac @node Forbidden Patterns @subsection Forbidden Patterns @cindex Forbidden patterns @cindex Patterns, forbidden M4sugar provides a means to define suspicious patterns, patterns describing tokens which should not be found in the output. For instance, if an Autoconf @file{configure} script includes tokens such as @samp{AC_DEFINE}, or @samp{dnl}, then most probably something went wrong (typically a macro was not evaluated because of overquotation). M4sugar forbids all the tokens matching @samp{^m4_} and @samp{^dnl$}. @defmac m4_pattern_forbid (@var{pattern}) @msindex{pattern_forbid} Declare that no token matching @var{pattern} must be found in the output. Comments are not checked; this can be a problem if, for instance, you have some macro left unexpanded after an @samp{#include}. No consensus is currently found in the Autoconf community, as some people consider it should be valid to name macros in comments (which doesn't make sense to the author of this documentation, as @samp{#}-comments should document the output, not the input, documented by @samp{dnl} comments). @end defmac Of course, you might encounter exceptions to these generic rules, for instance you might have to refer to @samp{$m4_flags}. @defmac m4_pattern_allow (@var{pattern}) @msindex{pattern_allow} Any token matching @var{pattern} is allowed, including if it matches an @code{m4_pattern_forbid} pattern. @end defmac @node Programming in M4sh @section Programming in M4sh @c FIXME: Eventually will become a chapter, as it is not related to @c programming in M4 per se. M4sh, pronounced ``mash'', is aiming at producing portable Bourne shell scripts. This name was coined by Lars J. Aas, who notes that, according to the Webster's Revised Unabridged Dictionary (1913): @quotation Mash \Mash\, n. [Akin to G. meisch, maisch, meische, maische, mash, wash, and prob.@: to AS. miscian to mix. See ``Mix''.] @enumerate 1 @item A mass of mixed ingredients reduced to a soft pulpy state by beating or pressure@enddots{} @item A mixture of meal or bran and water fed to animals. @item A mess; trouble. [Obs.] --Beau.@: & Fl. @end enumerate @end quotation For the time being, it is not mature enough to be widely used. M4sh provides portable alternatives for some common shell constructs that unfortunately are not portable in practice. @c Deprecated, to be replaced by a better API @ignore @defmac AS_BASENAME (@var{file-name}) @asindex{BASENAME} Output the non-directory portion of @var{file-name}. For example, if @code{$file} is @samp{/one/two/three}, the command @code{base=`AS_BASENAME(["$file"])`} sets @code{base} to @samp{three}. @end defmac @end ignore @defmac AS_BOURNE_COMPATIBLE @asindex{BOURNE_COMPATIBLE} Set up the shell to be more compatible with the Bourne shell as standardized by Posix, if possible. This may involve setting environment variables, or setting options, or similar implementation-specific actions. @end defmac @defmac AS_CASE (@var{word}, @ovar{pattern1}, @ovar{if-matched1}, @dots{}, @ovar{default}) @asindex{CASE} Expand into a shell @samp{case} statement, where @var{word} is matched against one or more patterns. @var{if-matched} is run if the corresponding pattern matched @var{word}, else @var{default} is run. @end defmac @defmac AS_DIRNAME (@var{file-name}) @asindex{DIRNAME} Output the directory portion of @var{file-name}. For example, if @code{$file} is @samp{/one/two/three}, the command @code{dir=`AS_DIRNAME(["$file"])`} sets @code{dir} to @samp{/one/two}. @end defmac @defmac AS_IF (@var{test1}, @ovar{run-if-true1}, @dots{}, @ovar{run-if-false}) @asindex{IF} Run shell code @var{test1}. If @var{test1} exits with a zero status then run shell code @var{run-if-true1}, else examine further tests. If no test exits with a zero status, run shell code @var{run-if-false}, with simplifications if either @var{run-if-true1} or @var{run-if-false1} is empty. For example, @example AS_IF([test "$foo" = yes], [HANDLE_FOO([yes])], [test "$foo" != no], [HANDLE_FOO([maybe])], [echo foo not specified]) @end example @noindent ensures any required macros of @code{HANDLE_FOO} are expanded before the first test. @end defmac @defmac AS_MKDIR_P (@var{file-name}) @asindex{MKDIR_P} Make the directory @var{file-name}, including intervening directories as necessary. This is equivalent to @samp{mkdir -p @var{file-name}}, except that it is portable to older versions of @command{mkdir} that lack support for the @option{-p} option. Also, @code{AS_MKDIR_P} succeeds if @var{file-name} is a symbolic link to an existing directory, even though Posix is unclear whether @samp{mkdir -p} should succeed in that case. If creation of @var{file-name} fails, exit the script. Also see the @code{AC_PROG_MKDIR_P} macro (@pxref{Particular Programs}). @end defmac @defmac AS_SHELL_SANITIZE @asindex{SHELL_SANITIZE} Initialize the shell suitably for @code{configure} scripts. This has the effect of @code{AS_BOURNE_COMPATIBLE}, and sets some other environment variables for predictable results from configuration tests. For example, it sets @env{LC_ALL} to change to the default C locale. @xref{Special Shell Variables}. @end defmac @defmac AS_TR_CPP (@var{expression}) @asindex{TR_CPP} Transform @var{expression} into a valid right-hand side for a C @code{#define}. For example: @example # This outputs "#define HAVE_CHAR_P 1". type="char *" echo "#define AS_TR_CPP([HAVE_$type]) 1" @end example @end defmac @defmac AS_TR_SH (@var{expression}) @asindex{TR_SH} Transform @var{expression} into a valid shell variable name. For example: @example # This outputs "Have it!". header="sys/some file.h" AS_TR_SH([HAVE_$header])=yes if test "$HAVE_sys_some_file_h" = yes; then echo "Have it!"; fi @end example @end defmac @defmac AS_SET_CATFILE (@var{var}, @var{dir}, @var{file}) @asindex{SET_CATFILE} Set the shell variable @var{var} to @var{dir}/@var{file}, but optimizing the common cases (@var{dir} or @var{file} is @samp{.}, @var{file} is absolute, etc.). @end defmac @node File Descriptor Macros @section File Descriptor Macros @cindex input @cindex standard input @cindex file descriptors @cindex descriptors @cindex low-level output @cindex output, low-level The following macros define file descriptors used to output messages (or input values) from @file{configure} scripts. For example: @example echo "$wombats found" >&AS_MESSAGE_LOG_FD echo 'Enter desired kangaroo count:' >&AS_MESSAGE_FD read kangaroos <&AS_ORIGINAL_STDIN_FD` @end example @noindent However doing so is seldom needed, because Autoconf provides higher level macros as described below. @defmac AS_MESSAGE_FD @asindex{MESSAGE_FD} The file descriptor for @samp{checking for...} messages and results. Normally this directs messages to the standard output, however when @command{configure} is run with the @option{-q} option, messages sent to @code{AS_MESSAGE_FD} are discarded. If you want to display some messages, consider using one of the printing macros (@pxref{Printing Messages}) instead. Copies of messages output via these macros are also recorded in @file{config.log}. @end defmac @defmac AS_MESSAGE_LOG_FD @asindex{MESSAGE_LOG_FD} The file descriptor for messages logged to @file{config.log}. Macros that run tools, like @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}), redirect all output to this descriptor. You may want to do so if you develop such a low-level macro. @end defmac @defmac AS_ORIGINAL_STDIN_FD @asindex{ORIGINAL_STDIN_FD} The file descriptor for the original standard input. When @command{configure} runs, it may accidentally execute an interactive command that has the same name as the non-interactive meant to be used or checked. If the standard input was the terminal, such interactive programs would cause @command{configure} to stop, pending some user input. Therefore @command{configure} redirects its standard input from @file{/dev/null} during its initialization. This is not normally a problem, since @command{configure} normally does not need user input. In the extreme case where your @file{configure} script really needs to obtain some values from the original standard input, you can read them explicitly from @code{AS_ORIGINAL_STDIN_FD}. @end defmac @c =================================================== Writing Autoconf Macros. @node Writing Autoconf Macros @chapter Writing Autoconf Macros When you write a feature test that could be applicable to more than one software package, the best thing to do is encapsulate it in a new macro. Here are some instructions and guidelines for writing Autoconf macros. @menu * Macro Definitions:: Basic format of an Autoconf macro * Macro Names:: What to call your new macros * Reporting Messages:: Notifying @command{autoconf} users * Dependencies Between Macros:: What to do when macros depend on other macros * Obsoleting Macros:: Warning about old ways of doing things * Coding Style:: Writing Autoconf macros @`a la Autoconf @end menu @node Macro Definitions @section Macro Definitions @acindex{DEFUN} Autoconf macros are defined using the @code{AC_DEFUN} macro, which is similar to the M4 builtin @code{m4_define} macro. In addition to defining a macro, @code{AC_DEFUN} adds to it some code that is used to constrain the order in which macros are called (@pxref{Prerequisite Macros}). An Autoconf macro definition looks like this: @example AC_DEFUN(@var{macro-name}, @var{macro-body}) @end example You can refer to any arguments passed to the macro as @samp{$1}, @samp{$2}, etc. @xref{Definitions, , How to define new macros, m4.info, @acronym{GNU} M4}, for more complete information on writing M4 macros. Be sure to properly quote both the @var{macro-body} @emph{and} the @var{macro-name} to avoid any problems if the macro happens to have been previously defined. Each macro should have a header comment that gives its prototype, and a brief description. When arguments have default values, display them in the prototype. For example: @example # AC_MSG_ERROR(ERROR, [EXIT-STATUS = 1]) # -------------------------------------- m4_define([AC_MSG_ERROR], [@{ AS_MESSAGE([error: $1], [2]) exit m4_default([$2], [1]); @}]) @end example Comments about the macro should be left in the header comment. Most other comments make their way into @file{configure}, so just keep using @samp{#} to introduce comments. @cindex @code{dnl} If you have some special comments about pure M4 code, comments that make no sense in @file{configure} and in the header comment, then use the builtin @code{dnl}: it causes M4 to discard the text through the next newline. Keep in mind that @code{dnl} is rarely needed to introduce comments; @code{dnl} is more useful to get rid of the newlines following macros that produce no output, such as @code{AC_REQUIRE}. @node Macro Names @section Macro Names All of the Autoconf macros have all-uppercase names starting with @samp{AC_} to prevent them from accidentally conflicting with other text. All shell variables that they use for internal purposes have mostly-lowercase names starting with @samp{ac_}. To ensure that your macros don't conflict with present or future Autoconf macros, you should prefix your own macro names and any shell variables they use with some other sequence. Possibilities include your initials, or an abbreviation for the name of your organization or software package. Most of the Autoconf macros' names follow a structured naming convention that indicates the kind of feature check by the name. The macro names consist of several words, separated by underscores, going from most general to most specific. The names of their cache variables use the same convention (@pxref{Cache Variable Names}, for more information on them). The first word of the name after @samp{AC_} usually tells the category of the feature being tested. Here are the categories used in Autoconf for specific test macros, the kind of macro that you are more likely to write. They are also used for cache variables, in all-lowercase. Use them where applicable; where they're not, invent your own categories. @table @code @item C C language builtin features. @item DECL Declarations of C variables in header files. @item FUNC Functions in libraries. @item GROUP Posix group owners of files. @item HEADER Header files. @item LIB C libraries. @item PATH Absolute names of files, including programs. @item PROG The base names of programs. @item MEMBER Members of aggregates. @item SYS Operating system features. @item TYPE C builtin or declared types. @item VAR C variables in libraries. @end table After the category comes the name of the particular feature being tested. Any further words in the macro name indicate particular aspects of the feature. For example, @code{AC_PROG_CC_STDC} checks whether the C compiler supports @acronym{ISO} Standard C. An internal macro should have a name that starts with an underscore; Autoconf internals should therefore start with @samp{_AC_}. Additionally, a macro that is an internal subroutine of another macro should have a name that starts with an underscore and the name of that other macro, followed by one or more words saying what the internal macro does. For example, @code{AC_PATH_X} has internal macros @code{_AC_PATH_X_XMKMF} and @code{_AC_PATH_X_DIRECT}. @node Reporting Messages @section Reporting Messages @cindex Messages, from @command{autoconf} When macros statically diagnose abnormal situations, benign or fatal, they should report them using these macros. For dynamic issues, i.e., when @command{configure} is run, see @ref{Printing Messages}. @defmac AC_DIAGNOSE (@var{category}, @var{message}) @acindex{DIAGNOSE} Report @var{message} as a warning (or as an error if requested by the user) if warnings of the @var{category} are turned on. You are encouraged to use standard categories, which currently include: @table @samp @item all messages that don't fall into one of the following categories. Use of an empty @var{category} is equivalent. @item cross related to cross compilation issues. @item obsolete use of an obsolete construct. @item syntax dubious syntactic constructs, incorrectly ordered macro calls. @end table @end defmac @defmac AC_WARNING (@var{message}) @acindex{WARNING} Equivalent to @samp{AC_DIAGNOSE([syntax], @var{message})}, but you are strongly encouraged to use a finer grained category. @end defmac @defmac AC_FATAL (@var{message}) @acindex{FATAL} Report a severe error @var{message}, and have @command{autoconf} die. @end defmac When the user runs @samp{autoconf -W error}, warnings from @code{AC_DIAGNOSE} and @code{AC_WARNING} are reported as error, see @ref{autoconf Invocation}. @node Dependencies Between Macros @section Dependencies Between Macros @cindex Dependencies between macros Some Autoconf macros depend on other macros having been called first in order to work correctly. Autoconf provides a way to ensure that certain macros are called if needed and a way to warn the user if macros are called in an order that might cause incorrect operation. @menu * Prerequisite Macros:: Ensuring required information * Suggested Ordering:: Warning about possible ordering problems * One-Shot Macros:: Ensuring a macro is called only once @end menu @node Prerequisite Macros @subsection Prerequisite Macros @cindex Prerequisite macros @cindex Macros, prerequisites A macro that you write might need to use values that have previously been computed by other macros. For example, @code{AC_DECL_YYTEXT} examines the output of @code{flex} or @code{lex}, so it depends on @code{AC_PROG_LEX} having been called first to set the shell variable @code{LEX}. Rather than forcing the user of the macros to keep track of the dependencies between them, you can use the @code{AC_REQUIRE} macro to do it automatically. @code{AC_REQUIRE} can ensure that a macro is only called if it is needed, and only called once. @defmac AC_REQUIRE (@var{macro-name}) @acindex{REQUIRE} If the M4 macro @var{macro-name} has not already been called, call it (without any arguments). Make sure to quote @var{macro-name} with square brackets. @var{macro-name} must have been defined using @code{AC_DEFUN} or else contain a call to @code{AC_PROVIDE} to indicate that it has been called. @code{AC_REQUIRE} must be used inside a macro defined by @code{AC_DEFUN}; it must not be called from the top level. @end defmac @code{AC_REQUIRE} is often misunderstood. It really implements dependencies between macros in the sense that if one macro depends upon another, the latter is expanded @emph{before} the body of the former. To be more precise, the required macro is expanded before the outermost defined macro in the current expansion stack. In particular, @samp{AC_REQUIRE([FOO])} is not replaced with the body of @code{FOO}. For instance, this definition of macros: @example @group AC_DEFUN([TRAVOLTA], [test "$body_temperature_in_celsius" -gt "38" && dance_floor=occupied]) AC_DEFUN([NEWTON_JOHN], [test "$hair_style" = "curly" && dance_floor=occupied]) @end group @group AC_DEFUN([RESERVE_DANCE_FLOOR], [if date | grep '^Sat.*pm' >/dev/null 2>&1; then AC_REQUIRE([TRAVOLTA]) AC_REQUIRE([NEWTON_JOHN]) fi]) @end group @end example @noindent with this @file{configure.ac} @example AC_INIT([Dance Manager], [1.0], [bug-dance@@example.org]) RESERVE_DANCE_FLOOR if test "$dance_floor" = occupied; then AC_MSG_ERROR([cannot pick up here, let's move]) fi @end example @noindent does not leave you with a better chance to meet a kindred soul at other times than Saturday night since it expands into: @example @group test "$body_temperature_in_Celsius" -gt "38" && dance_floor=occupied test "$hair_style" = "curly" && dance_floor=occupied fi if date | grep '^Sat.*pm' >/dev/null 2>&1; then fi @end group @end example This behavior was chosen on purpose: (i) it prevents messages in required macros from interrupting the messages in the requiring macros; (ii) it avoids bad surprises when shell conditionals are used, as in: @example @group if @dots{}; then AC_REQUIRE([SOME_CHECK]) fi @dots{} SOME_CHECK @end group @end example The helper macros @code{AS_IF} and @code{AS_CASE} may be used to enforce expansion of required macros outside of shell conditional constructs. You are furthermore encouraged to put all @code{AC_REQUIRE} calls at the beginning of a macro. You can use @code{dnl} to avoid the empty lines they leave. @node Suggested Ordering @subsection Suggested Ordering @cindex Macros, ordering @cindex Ordering macros Some macros should be run before another macro if both are called, but neither @emph{requires} that the other be called. For example, a macro that changes the behavior of the C compiler should be called before any macros that run the C compiler. Many of these dependencies are noted in the documentation. Autoconf provides the @code{AC_BEFORE} macro to warn users when macros with this kind of dependency appear out of order in a @file{configure.ac} file. The warning occurs when creating @command{configure} from @file{configure.ac}, not when running @command{configure}. For example, @code{AC_PROG_CPP} checks whether the C compiler can run the C preprocessor when given the @option{-E} option. It should therefore be called after any macros that change which C compiler is being used, such as @code{AC_PROG_CC}. So @code{AC_PROG_CC} contains: @example AC_BEFORE([$0], [AC_PROG_CPP])dnl @end example @noindent This warns the user if a call to @code{AC_PROG_CPP} has already occurred when @code{AC_PROG_CC} is called. @defmac AC_BEFORE (@var{this-macro-name}, @var{called-macro-name}) @acindex{BEFORE} Make M4 print a warning message to the standard error output if @var{called-macro-name} has already been called. @var{this-macro-name} should be the name of the macro that is calling @code{AC_BEFORE}. The macro @var{called-macro-name} must have been defined using @code{AC_DEFUN} or else contain a call to @code{AC_PROVIDE} to indicate that it has been called. @end defmac @node One-Shot Macros @subsection One-Shot Macros @cindex One-shot macros @cindex Macros, called once Some macros should be called only once, either because calling them multiple time is unsafe, or because it is bad style. For instance Autoconf ensures that @code{AC_CANONICAL_BUILD} and cousins (@pxref{Canonicalizing}) are evaluated only once, because it makes no sense to run these expensive checks more than once. Such one-shot macros can be defined using @code{AC_DEFUN_ONCE}. @defmac AC_DEFUN_ONCE (@var{macro-name}, @var{macro-body}) @acindex{DEFUN_ONCE} Declare macro @var{macro-name} like @code{AC_DEFUN} would (@pxref{Macro Definitions}), and emit a warning any time the macro is called more than once. @end defmac Obviously it is not sensible to evaluate a macro defined by @code{AC_DEFUN_ONCE} in a macro defined by @code{AC_DEFUN}. Most of the time you want to use @code{AC_REQUIRE} (@pxref{Prerequisite Macros}). @node Obsoleting Macros @section Obsoleting Macros @cindex Obsoleting macros @cindex Macros, obsoleting Configuration and portability technology has evolved over the years. Often better ways of solving a particular problem are developed, or ad-hoc approaches are systematized. This process has occurred in many parts of Autoconf. One result is that some of the macros are now considered @dfn{obsolete}; they still work, but are no longer considered the best thing to do, hence they should be replaced with more modern macros. Ideally, @command{autoupdate} should replace the old macro calls with their modern implementation. Autoconf provides a simple means to obsolete a macro. @defmac AU_DEFUN (@var{old-macro}, @var{implementation}, @ovar{message}) @auindex{DEFUN} Define @var{old-macro} as @var{implementation}. The only difference with @code{AC_DEFUN} is that the user is warned that @var{old-macro} is now obsolete. If she then uses @command{autoupdate}, the call to @var{old-macro} is replaced by the modern @var{implementation}. @var{message} should include information on what to do after running @command{autoupdate}; @command{autoupdate} prints it as a warning, and includes it in the updated @file{configure.ac} file. The details of this macro are hairy: if @command{autoconf} encounters an @code{AU_DEFUN}ed macro, all macros inside its second argument are expanded as usual. However, when @command{autoupdate} is run, only M4 and M4sugar macros are expanded here, while all other macros are disabled and appear literally in the updated @file{configure.ac}. @end defmac @defmac AU_ALIAS (@var{old-name}, @var{new-name}) @auindex{ALIAS} Used if the @var{old-name} is to be replaced by a call to @var{new-macro} with the same parameters. This happens for example if the macro was renamed. @end defmac @node Coding Style @section Coding Style @cindex Coding style The Autoconf macros follow a strict coding style. You are encouraged to follow this style, especially if you intend to distribute your macro, either by contributing it to Autoconf itself, or via other means. The first requirement is to pay great attention to the quotation. For more details, see @ref{Autoconf Language}, and @ref{M4 Quotation}. Do not try to invent new interfaces. It is likely that there is a macro in Autoconf that resembles the macro you are defining: try to stick to this existing interface (order of arguments, default values, etc.). We @emph{are} conscious that some of these interfaces are not perfect; nevertheless, when harmless, homogeneity should be preferred over creativity. Be careful about clashes both between M4 symbols and between shell variables. If you stick to the suggested M4 naming scheme (@pxref{Macro Names}), you are unlikely to generate conflicts. Nevertheless, when you need to set a special value, @emph{avoid using a regular macro name}; rather, use an ``impossible'' name. For instance, up to version 2.13, the macro @code{AC_SUBST} used to remember what @var{symbol} macros were already defined by setting @code{AC_SUBST_@var{symbol}}, which is a regular macro name. But since there is a macro named @code{AC_SUBST_FILE}, it was just impossible to @samp{AC_SUBST(FILE)}! In this case, @code{AC_SUBST(@var{symbol})} or @code{_AC_SUBST(@var{symbol})} should have been used (yes, with the parentheses). @c or better yet, high-level macros such as @code{m4_expand_once} No Autoconf macro should ever enter the user-variable name space; i.e., except for the variables that are the actual result of running the macro, all shell variables should start with @code{ac_}. In addition, small macros or any macro that is likely to be embedded in other macros should be careful not to use obvious names. @cindex @code{dnl} Do not use @code{dnl} to introduce comments: most of the comments you are likely to write are either header comments which are not output anyway, or comments that should make their way into @file{configure}. There are exceptional cases where you do want to comment special M4 constructs, in which case @code{dnl} is right, but keep in mind that it is unlikely. M4 ignores the leading blanks and newlines before each argument. Use this feature to indent in such a way that arguments are (more or less) aligned with the opening parenthesis of the macro being called. For instance, instead of @example AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2, [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) @end example @noindent write @example AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) @end example @noindent or even @example AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) @end example When using @code{AC_RUN_IFELSE} or any macro that cannot work when cross-compiling, provide a pessimistic value (typically @samp{no}). Feel free to use various tricks to prevent auxiliary tools, such as syntax-highlighting editors, from behaving improperly. For instance, instead of: @example m4_bpatsubst([$1], [$"]) @end example @noindent use @example m4_bpatsubst([$1], [$""]) @end example @noindent so that Emacsen do not open an endless ``string'' at the first quote. For the same reasons, avoid: @example test $[#] != 0 @end example @noindent and use: @example test $[@@%:@@] != 0 @end example @noindent Otherwise, the closing bracket would be hidden inside a @samp{#}-comment, breaking the bracket-matching highlighting from Emacsen. Note the preferred style to escape from M4: @samp{$[1]}, @samp{$[@@]}, etc. Do not escape when it is unnecessary. Common examples of useless quotation are @samp{[$]$1} (write @samp{$$1}), @samp{[$]var} (use @samp{$var}), etc. If you add portability issues to the picture, you'll prefer @samp{$@{1+"$[@@]"@}} to @samp{"[$]@@"}, and you'll prefer do something better than hacking Autoconf @code{:-)}. When using @command{sed}, don't use @option{-e} except for indenting purposes. With the @code{s} and @code{y} commands, the preferred separator is @samp{/} unless @samp{/} itself might appear in the pattern or replacement, in which case you should use @samp{|}, or optionally @samp{,} if you know the pattern and replacement cannot contain a file name. If none of these characters will do, choose a printable character that cannot appear in the pattern or replacement. Characters from the set @samp{"#$&'()*;<=>?`|~} are good choices if the pattern or replacement might contain a file name, since they have special meaning to the shell and are less likely to occur in file names. @xref{Macro Definitions}, for details on how to define a macro. If a macro doesn't use @code{AC_REQUIRE}, is expected to never be the object of an @code{AC_REQUIRE} directive, and macros required by other macros inside arguments do not need to be expanded before this macro, then use @code{m4_define}. In case of doubt, use @code{AC_DEFUN}. All the @code{AC_REQUIRE} statements should be at the beginning of the macro, and each statement should be followed by @code{dnl}. You should not rely on the number of arguments: instead of checking whether an argument is missing, test that it is not empty. It provides both a simpler and a more predictable interface to the user, and saves room for further arguments. Unless the macro is short, try to leave the closing @samp{])} at the beginning of a line, followed by a comment that repeats the name of the macro being defined. This introduces an additional newline in @command{configure}; normally, that is not a problem, but if you want to remove it you can use @samp{[]dnl} on the last line. You can similarly use @samp{[]dnl} after a macro call to remove its newline. @samp{[]dnl} is recommended instead of @samp{dnl} to ensure that M4 does not interpret the @samp{dnl} as being attached to the preceding text or macro output. For example, instead of: @example AC_DEFUN([AC_PATH_X], [AC_MSG_CHECKING([for X]) AC_REQUIRE_CPP() @r{# @dots{}omitted@dots{}} AC_MSG_RESULT([libraries $x_libraries, headers $x_includes]) fi]) @end example @noindent you would write: @example AC_DEFUN([AC_PATH_X], [AC_REQUIRE_CPP()[]dnl AC_MSG_CHECKING([for X]) @r{# @dots{}omitted@dots{}} AC_MSG_RESULT([libraries $x_libraries, headers $x_includes]) fi[]dnl ])# AC_PATH_X @end example If the macro is long, try to split it into logical chunks. Typically, macros that check for a bug in a function and prepare its @code{AC_LIBOBJ} replacement should have an auxiliary macro to perform this setup. Do not hesitate to introduce auxiliary macros to factor your code. In order to highlight the recommended coding style, here is a macro written the old way: @example dnl Check for EMX on OS/2. dnl _AC_EMXOS2 AC_DEFUN(_AC_EMXOS2, [AC_CACHE_CHECK(for EMX OS/2 environment, ac_cv_emxos2, [AC_COMPILE_IFELSE([AC_LANG_PROGRAM(, return __EMX__;)], ac_cv_emxos2=yes, ac_cv_emxos2=no)]) test "$ac_cv_emxos2" = yes && EMXOS2=yes]) @end example @noindent and the new way: @example # _AC_EMXOS2 # ---------- # Check for EMX on OS/2. m4_define([_AC_EMXOS2], [AC_CACHE_CHECK([for EMX OS/2 environment], [ac_cv_emxos2], [AC_COMPILE_IFELSE([AC_LANG_PROGRAM([], [return __EMX__;])], [ac_cv_emxos2=yes], [ac_cv_emxos2=no])]) test "$ac_cv_emxos2" = yes && EMXOS2=yes[]dnl ])# _AC_EMXOS2 @end example @c ============================================= Portable Shell Programming @node Portable Shell @chapter Portable Shell Programming @cindex Portable shell programming When writing your own checks, there are some shell-script programming techniques you should avoid in order to make your code portable. The Bourne shell and upward-compatible shells like the Korn shell and Bash have evolved over the years, but to prevent trouble, do not take advantage of features that were added after Unix version 7, circa 1977 (@pxref{Systemology}). You should not use shell functions, aliases, negated character classes, or other features that are not found in all Bourne-compatible shells; restrict yourself to the lowest common denominator. Even @code{unset} is not supported by all shells! Some ancient systems have quite small limits on the length of the @samp{#!} line; for instance, 32 bytes (not including the newline) on SunOS 4. A few ancient 4.2@acronym{BSD} based systems (such as Dynix circa 1984) required a single space between the @samp{#!} and the @samp{/}. However, these ancient systems are no longer of practical concern. The set of external programs you should run in a @command{configure} script is fairly small. @xref{Utilities in Makefiles, , Utilities in Makefiles, standards, @acronym{GNU} Coding Standards}, for the list. This restriction allows users to start out with a fairly small set of programs and build the rest, avoiding too many interdependencies between packages. Some of these external utilities have a portable subset of features; see @ref{Limitations of Usual Tools}. There are other sources of documentation about shells. The specification for the Posix @uref{http://www.opengroup.org/@/susv3/@/utilities/@/xcu_chap02.html, Shell Command Language}, though more generous than the restrictive shell subset described above, is fairly portable nowadays. Also please see @uref{http://www.faqs.org/@/faqs/@/unix-faq/@/shell/, the Shell FAQs}. @menu * Shellology:: A zoology of shells * Here-Documents:: Quirks and tricks * File Descriptors:: FDs and redirections * File System Conventions:: File names * Shell Substitutions:: Variable and command expansions * Assignments:: Varying side effects of assignments * Parentheses:: Parentheses in shell scripts * Slashes:: Slashes in shell scripts * Special Shell Variables:: Variables you should not change * Limitations of Builtins:: Portable use of not so portable /bin/sh * Limitations of Usual Tools:: Portable use of portable tools @end menu @node Shellology @section Shellology @cindex Shellology There are several families of shells, most prominently the Bourne family and the C shell family which are deeply incompatible. If you want to write portable shell scripts, avoid members of the C shell family. The @uref{http://www.faqs.org/@/faqs/@/unix-faq/@/shell/@/shell-differences/, the Shell difference FAQ} includes a small history of Posix shells, and a comparison between several of them. Below we describe some of the members of the Bourne shell family. @table @asis @item Ash @cindex Ash Ash is often used on @acronym{GNU}/Linux and @acronym{BSD} systems as a light-weight Bourne-compatible shell. Ash 0.2 has some bugs that are fixed in the 0.3.x series, but portable shell scripts should work around them, since version 0.2 is still shipped with many @acronym{GNU}/Linux distributions. To be compatible with Ash 0.2: @itemize @minus @item don't use @samp{$?} after expanding empty or unset variables, or at the start of an @command{eval}: @example foo= false $foo echo "Do not use it: $?" false eval 'echo "Do not use it: $?"' @end example @item don't use command substitution within variable expansion: @example cat $@{FOO=`bar`@} @end example @item beware that single builtin substitutions are not performed by a subshell, hence their effect applies to the current shell! @xref{Shell Substitutions}, item ``Command Substitution''. @end itemize @item Bash @cindex Bash To detect whether you are running Bash, test whether @code{BASH_VERSION} is set. To require Posix compatibility, run @samp{set -o posix}. @xref{Bash POSIX Mode, , Bash Posix Mode, bash, The @acronym{GNU} Bash Reference Manual}, for details. @item Bash 2.05 and later @cindex Bash 2.05 and later Versions 2.05 and later of Bash use a different format for the output of the @command{set} builtin, designed to make evaluating its output easier. However, this output is not compatible with earlier versions of Bash (or with many other shells, probably). So if you use Bash 2.05 or higher to execute @command{configure}, you'll need to use Bash 2.05 for all other build tasks as well. @item Ksh @cindex Ksh @cindex Korn shell @prindex @samp{ksh} @prindex @samp{ksh88} @prindex @samp{ksh93} The Korn shell is compatible with the Bourne family and it mostly conforms to Posix. It has two major variants commonly called @samp{ksh88} and @samp{ksh93}, named after the years of initial release. It is usually called @command{ksh}, but is called @command{sh} on some hosts if you set your path appropriately. Solaris systems have three variants: @prindex @command{/usr/bin/ksh} on Solaris @command{/usr/bin/ksh} is @samp{ksh88}; it is standard on Solaris 2.0 and later. @prindex @command{/usr/xpg4/bin/sh} on Solaris @command{/usr/xpg4/bin/sh} is a Posix-compliant variant of @samp{ksh88}; it is standard on Solaris 9 and later. @prindex @command{/usr/dt/bin/dtksh} on Solaris @command{/usr/dt/bin/dtksh} is @samp{ksh93}. Variants that are not standard may be parts of optional packages. There is no extra charge for these packages, but they are not part of a minimal OS install and therefore some installations may not have it. Starting with Tru64 Version 4.0, the Korn shell @command{/usr/bin/ksh} is also available as @command{/usr/bin/posix/sh}. If the environment variable @env{BIN_SH} is set to @code{xpg4}, subsidiary invocations of the standard shell conform to Posix. @item Pdksh @prindex @samp{pdksh} A public-domain clone of the Korn shell called @command{pdksh} is widely available: it has most of the @samp{ksh88} features along with a few of its own. It usually sets @code{KSH_VERSION}, except if invoked as @command{/bin/sh} on Open@acronym{BSD}, and similarly to Bash you can require Posix compatibility by running @samp{set -o posix}. Unfortunately, with @command{pdksh} 5.2.14 (the latest stable version as of February 2006) Posix mode is buggy and causes @command{pdksh} to depart from Posix in at least one respect: @example $ @kbd{echo "`echo \"hello\"`"} hello $ @kbd{set -o posix} $ @kbd{echo "`echo \"hello\"`"} "hello" @end example The last line of output contains spurious quotes. This is yet another reason why portable shell code should not contain @code{"`@dots{}\"@dots{}\"@dots{}`"} constructs (@pxref{Shell Substitutions}). @item Zsh @cindex Zsh To detect whether you are running @command{zsh}, test whether @code{ZSH_VERSION} is set. By default @command{zsh} is @emph{not} compatible with the Bourne shell: you must execute @samp{emulate sh}, and for @command{zsh} versions before 3.1.6-dev-18 you must also set @code{NULLCMD} to @samp{:}. @xref{Compatibility, , Compatibility, zsh, The Z Shell Manual}, for details. The default Mac OS X @command{sh} was originally Zsh; it was changed to Bash in Mac OS X 10.2. @end table The following discussion between Russ Allbery and Robert Lipe is worth reading: @noindent Russ Allbery: @quotation The @acronym{GNU} assumption that @command{/bin/sh} is the one and only shell leads to a permanent deadlock. Vendors don't want to break users' existing shell scripts, and there are some corner cases in the Bourne shell that are not completely compatible with a Posix shell. Thus, vendors who have taken this route will @emph{never} (OK@dots{}``never say never'') replace the Bourne shell (as @command{/bin/sh}) with a Posix shell. @end quotation @noindent Robert Lipe: @quotation This is exactly the problem. While most (at least most System V's) do have a Bourne shell that accepts shell functions most vendor @command{/bin/sh} programs are not the Posix shell. So while most modern systems do have a shell @emph{somewhere} that meets the Posix standard, the challenge is to find it. @end quotation @node Here-Documents @section Here-Documents @cindex Here-documents @cindex Shell here-documents Don't rely on @samp{\} being preserved just because it has no special meaning together with the next symbol. In the native @command{sh} on Open@acronym{BSD} 2.7 @samp{\"} expands to @samp{"} in here-documents with unquoted delimiter. As a general rule, if @samp{\\} expands to @samp{\} use @samp{\\} to get @samp{\}. With Open@acronym{BSD} 2.7's @command{sh} @example @group $ @kbd{cat < \" \\ > EOF} " \ @end group @end example @noindent and with Bash: @example @group bash-2.04$ @kbd{cat < \" \\ > EOF} \" \ @end group @end example Some shells mishandle large here-documents: for example, Solaris 10 @command{dtksh} and the UnixWare 7.1.1 Posix shell, which are derived from Korn shell version M-12/28/93d, mishandle braced variable expansion that crosses a 1024- or 4096-byte buffer boundary within a here-document. Only the part of the variable name after the boundary is used. For example, @code{$@{variable@}} could be replaced by the expansion of @code{$@{ble@}}. If the end of the variable name is aligned with the block boundary, the shell reports an error, as if you used @code{$@{@}}. Instead of @code{$@{variable-default@}}, the shell may expand @code{$@{riable-default@}}, or even @code{$@{fault@}}. This bug can often be worked around by omitting the braces: @code{$variable}. The bug was fixed in @samp{ksh93g} (1998-04-30) but as of 2006 many operating systems were still shipping older versions with the bug. Many older shells (including the Bourne shell) implement here-documents inefficiently. In particular, some shells can be extremely inefficient when a single statement contains many here-documents. For instance if your @file{configure.ac} includes something like: @example @group if ; then assume this and that else check this check that check something else @dots{} on and on forever @dots{} fi @end group @end example A shell parses the whole @code{if}/@code{fi} construct, creating temporary files for each here-document in it. Some shells create links for such here-documents on every @code{fork}, so that the clean-up code they had installed correctly removes them. It is creating the links that can take the shell forever. Moving the tests out of the @code{if}/@code{fi}, or creating multiple @code{if}/@code{fi} constructs, would improve the performance significantly. Anyway, this kind of construct is not exactly the typical use of Autoconf. In fact, it's even not recommended, because M4 macros can't look into shell conditionals, so we may fail to expand a macro when it was expanded before in a conditional path, and the condition turned out to be false at runtime, and we end up not executing the macro at all. @node File Descriptors @section File Descriptors @cindex Descriptors @cindex File descriptors @cindex Shell file descriptors Most shells, if not all (including Bash, Zsh, Ash), output traces on stderr, even for subshells. This might result in undesirable content if you meant to capture the standard-error output of the inner command: @example $ @kbd{ash -x -c '(eval "echo foo >&2") 2>stderr'} $ @kbd{cat stderr} + eval echo foo >&2 + echo foo foo $ @kbd{bash -x -c '(eval "echo foo >&2") 2>stderr'} $ @kbd{cat stderr} + eval 'echo foo >&2' ++ echo foo foo $ @kbd{zsh -x -c '(eval "echo foo >&2") 2>stderr'} @i{# Traces on startup files deleted here.} $ @kbd{cat stderr} +zsh:1> eval echo foo >&2 +zsh:1> echo foo foo @end example @noindent One workaround is to grep out uninteresting lines, hoping not to remove good ones. If you intend to redirect both standard error and standard output, redirect standard output first. This works better with @acronym{HP-UX}, since its shell mishandles tracing if standard error is redirected first: @example $ @kbd{sh -x -c ': 2>err >out'} + : + 2> err $ @kbd{cat err} 1> out @end example Don't try to redirect the standard error of a command substitution. It must be done @emph{inside} the command substitution. When running @samp{: `cd /zorglub` 2>/dev/null} expect the error message to escape, while @samp{: `cd /zorglub 2>/dev/null`} works properly. It is worth noting that Zsh (but not Ash nor Bash) makes it possible in assignments though: @samp{foo=`cd /zorglub` 2>/dev/null}. Don't redirect the same file descriptor several times, as you are doomed to failure under Ultrix. @example ULTRIX V4.4 (Rev. 69) System #31: Thu Aug 10 19:42:23 GMT 1995 UWS V4.4 (Rev. 11) $ @kbd{eval 'echo matter >fullness' >void} illegal io $ @kbd{eval '(echo matter >fullness)' >void} illegal io $ @kbd{(eval '(echo matter >fullness)') >void} Ambiguous output redirect. @end example @noindent In each case the expected result is of course @file{fullness} containing @samp{matter} and @file{void} being empty. Don't rely on file descriptors 0, 1, and 2 remaining closed in a subsidiary program. If any of these descriptors is closed, the operating system may open an unspecified file for the descriptor in the new process image. Posix says this may be done only if the subsidiary program is set-user-ID or set-group-ID, but @acronym{HP-UX} 11.23 does it even for ordinary programs. Don't rely on open file descriptors being open in child processes. In @command{ksh}, file descriptors above 2 which are opened using @samp{exec @var{n}>file} are closed by a subsequent @samp{exec} (such as that involved in the fork-and-exec which runs a program or script). Thus, using @command{sh}, we have: @example $ @kbd{cat ./descrips} #!/bin/sh - echo hello >&5 $ @kbd{exec 5>t} $ @kbd{./descrips} $ @kbd{cat t} $ hello @end example @noindent But using ksh: @example $ @kbd{exec 5>t} $ @kbd{./descrips} hello $ @kbd{cat t} $ @end example @noindent Within the process which runs the @samp{descrips} script, file descriptor 5 is closed. @acronym{DOS} variants cannot rename or remove open files, such as in @samp{mv foo bar >foo} or @samp{rm foo >foo}, even though this is perfectly portable among Posix hosts. A few ancient systems reserved some file descriptors. By convention, file descriptor 3 was opened to @file{/dev/tty} when you logged into Eighth Edition (1985) through Tenth Edition Unix (1989). File descriptor 4 had a special use on the Stardent/Kubota Titan (circa 1990), though we don't now remember what it was. Both these systems are obsolete, so it's now safe to treat file descriptors 3 and 4 like any other file descriptors. @node File System Conventions @section File System Conventions @cindex File system conventions Autoconf uses shell-script processing extensively, so the file names that it processes should not contain characters that are special to the shell. Special characters include space, tab, newline, @sc{nul}, and the following: @example " # $ & ' ( ) * ; < = > ? [ \ ` | @end example Also, file names should not begin with @samp{~} or @samp{-}, and should contain neither @samp{-} immediately after @samp{/} nor @samp{~} immediately after @samp{:}. On Posix-like platforms, directory names should not contain @samp{:}, as this runs afoul of @samp{:} used as the path separator. These restrictions apply not only to the files that you distribute, but also to the absolute file names of your source, build, and destination directories. On some Posix-like platforms, @samp{!} and @samp{^} are special too, so they should be avoided. Posix lets implementations treat leading @file{//} specially, but requires leading @file{///} and beyond to be equivalent to @file{/}. Most Unix variants treat @file{//} like @file{/}. However, some treat @file{//} as a ``super-root'' that can provide access to files that are not otherwise reachable from @file{/}. The super-root tradition began with Apollo Domain/OS, which died out long ago, but unfortunately Cygwin has revived it. While @command{autoconf} and friends are usually run on some Posix variety, they can be used on other systems, most notably @acronym{DOS} variants. This impacts several assumptions regarding file names. @noindent For example, the following code: @example case $foo_dir in /*) # Absolute ;; *) foo_dir=$dots$foo_dir ;; esac @end example @noindent fails to properly detect absolute file names on those systems, because they can use a drivespec, and usually use a backslash as directory separator. If you want to be portable to @acronym{DOS} variants (at the price of rejecting valid but oddball Posix file names like @file{a:\b}), you can check for absolute file names like this: @example case $foo_dir in [\\/]* | ?:[\\/]* ) # Absolute ;; *) foo_dir=$dots$foo_dir ;; esac @end example @noindent Make sure you quote the brackets if appropriate and keep the backslash as first character (@pxref{Limitations of Builtins}). Also, because the colon is used as part of a drivespec, these systems don't use it as path separator. When creating or accessing paths, you can use the @code{PATH_SEPARATOR} output variable instead. @command{configure} sets this to the appropriate value (@samp{:} or @samp{;}) when it starts up. File names need extra care as well. While @acronym{DOS} variants that are Posixy enough to run @command{autoconf} (such as @acronym{DJGPP}) are usually able to handle long file names properly, there are still limitations that can seriously break packages. Several of these issues can be easily detected by the @uref{ftp://ftp.gnu.org/gnu/non-gnu/doschk/doschk-1.1.tar.gz, doschk} package. A short overview follows; problems are marked with @sc{sfn}/@sc{lfn} to indicate where they apply: @sc{sfn} means the issues are only relevant to plain @acronym{DOS}, not to @acronym{DOS} under Microsoft Windows variants, while @sc{lfn} identifies problems that exist even under Microsoft Windows variants. @table @asis @item No multiple dots (@sc{sfn}) @acronym{DOS} cannot handle multiple dots in file names. This is an especially important thing to remember when building a portable configure script, as @command{autoconf} uses a .in suffix for template files. This is perfectly OK on Posix variants: @example AC_CONFIG_HEADERS([config.h]) AC_CONFIG_FILES([source.c foo.bar]) AC_OUTPUT @end example @noindent but it causes problems on @acronym{DOS}, as it requires @samp{config.h.in}, @samp{source.c.in} and @samp{foo.bar.in}. To make your package more portable to @acronym{DOS}-based environments, you should use this instead: @example AC_CONFIG_HEADERS([config.h:config.hin]) AC_CONFIG_FILES([source.c:source.cin foo.bar:foobar.in]) AC_OUTPUT @end example @item No leading dot (@sc{sfn}) @acronym{DOS} cannot handle file names that start with a dot. This is usually not important for @command{autoconf}. @item Case insensitivity (@sc{lfn}) @acronym{DOS} is case insensitive, so you cannot, for example, have both a file called @samp{INSTALL} and a directory called @samp{install}. This also affects @command{make}; if there's a file called @samp{INSTALL} in the directory, @samp{make install} does nothing (unless the @samp{install} target is marked as PHONY). @item The 8+3 limit (@sc{sfn}) Because the @acronym{DOS} file system only stores the first 8 characters of the file name and the first 3 of the extension, those must be unique. That means that @file{foobar-part1.c}, @file{foobar-part2.c} and @file{foobar-prettybird.c} all resolve to the same file name (@file{FOOBAR-P.C}). The same goes for @file{foo.bar} and @file{foo.bartender}. The 8+3 limit is not usually a problem under Microsoft Windows, as it uses numeric tails in the short version of file names to make them unique. However, a registry setting can turn this behavior off. While this makes it possible to share file trees containing long file names between @sc{sfn} and @sc{lfn} environments, it also means the above problem applies there as well. @item Invalid characters (@sc{lfn}) Some characters are invalid in @acronym{DOS} file names, and should therefore be avoided. In a @sc{lfn} environment, these are @samp{/}, @samp{\}, @samp{?}, @samp{*}, @samp{:}, @samp{<}, @samp{>}, @samp{|} and @samp{"}. In a @sc{sfn} environment, other characters are also invalid. These include @samp{+}, @samp{,}, @samp{[} and @samp{]}. @item Invalid names (@sc{lfn}) Some @acronym{DOS} file names are reserved, and cause problems if you try to use files with those names. These names include @file{CON}, @file{AUX}, @file{COM1}, @file{COM2}, @file{COM3}, @file{COM4}, @file{LPT1}, @file{LPT2}, @file{LPT3}, @file{NUL}, and @file{PRN}. File names are case insensitive, so even names like @file{aux/config.guess} are disallowed. @end table @node Shell Substitutions @section Shell Substitutions @cindex Shell substitutions Contrary to a persistent urban legend, the Bourne shell does not systematically split variables and back-quoted expressions, in particular on the right-hand side of assignments and in the argument of @code{case}. For instance, the following code: @example case "$given_srcdir" in .) top_srcdir="`echo "$dots" | sed 's,/$,,'`" ;; *) top_srcdir="$dots$given_srcdir" ;; esac @end example @noindent is more readable when written as: @example case $given_srcdir in .) top_srcdir=`echo "$dots" | sed 's,/$,,'` ;; *) top_srcdir=$dots$given_srcdir ;; esac @end example @noindent and in fact it is even @emph{more} portable: in the first case of the first attempt, the computation of @code{top_srcdir} is not portable, since not all shells properly understand @code{"`@dots{}"@dots{}"@dots{}`"}. Worse yet, not all shells understand @code{"`@dots{}\"@dots{}\"@dots{}`"} the same way. There is just no portable way to use double-quoted strings inside double-quoted back-quoted expressions (pfew!). @table @code @item $@@ @cindex @samp{"$@@"} One of the most famous shell-portability issues is related to @samp{"$@@"}. When there are no positional arguments, Posix says that @samp{"$@@"} is supposed to be equivalent to nothing, but the original Unix version 7 Bourne shell treated it as equivalent to @samp{""} instead, and this behavior survives in later implementations like Digital Unix 5.0. The traditional way to work around this portability problem is to use @samp{$@{1+"$@@"@}}. Unfortunately this method does not work with Zsh (3.x and 4.x), which is used on Mac OS X@. When emulating the Bourne shell, Zsh performs word splitting on @samp{$@{1+"$@@"@}}: @example zsh $ @kbd{emulate sh} zsh $ @kbd{for i in "$@@"; do echo $i; done} Hello World ! zsh $ @kbd{for i in $@{1+"$@@"@}; do echo $i; done} Hello World ! @end example @noindent Zsh handles plain @samp{"$@@"} properly, but we can't use plain @samp{"$@@"} because of the portability problems mentioned above. One workaround relies on Zsh's ``global aliases'' to convert @samp{$@{1+"$@@"@}} into @samp{"$@@"} by itself: @example test "$@{ZSH_VERSION+set@}" = set && alias -g '$@{1+"$@@"@}'='"$@@"' @end example A more conservative workaround is to avoid @samp{"$@@"} if it is possible that there may be no positional arguments. For example, instead of: @example cat conftest.c "$@@" @end example you can use this instead: @example case $# in 0) cat conftest.c;; *) cat conftest.c "$@@";; esac @end example Autoconf macros often use the @command{set} command to update @samp{$@@}, so if you are writing shell code intended for @command{configure} you should not assume that the value of @samp{$@@} persists for any length of time. @item $@{10@} @cindex positional parameters The 10th, 11th, @dots{} positional parameters can be accessed only after a @code{shift}. The 7th Edition shell reported an error if given @code{$@{10@}}, and Solaris 10 @command{/bin/sh} still acts that way: @example $ @kbd{set 1 2 3 4 5 6 7 8 9 10} $ @kbd{echo $@{10@}} bad substitution @end example @item $@{@var{var}:-@var{value}@} @c Info cannot handle `:' in index entries. @c @cindex $@{@var{var}:-@var{value}@} Old @acronym{BSD} shells, including the Ultrix @code{sh}, don't accept the colon for any shell substitution, and complain and die. @item $@{@var{var}=@var{literal}@} @cindex $@{@var{var}=@var{literal}@} Be sure to quote: @example : $@{var='Some words'@} @end example @noindent otherwise some shells, such as on Digital Unix V 5.0, die because of a ``bad substitution''. @sp 1 Solaris @command{/bin/sh} has a frightening bug in its interpretation of this. Imagine you need set a variable to a string containing @samp{@}}. This @samp{@}} character confuses Solaris @command{/bin/sh} when the affected variable was already set. This bug can be exercised by running: @example $ @kbd{unset foo} $ @kbd{foo=$@{foo='@}'@}} $ @kbd{echo $foo} @} $ @kbd{foo=$@{foo='@}' # no error; this hints to what the bug is} $ @kbd{echo $foo} @} $ @kbd{foo=$@{foo='@}'@}} $ @kbd{echo $foo} @}@} ^ ugh! @end example It seems that @samp{@}} is interpreted as matching @samp{$@{}, even though it is enclosed in single quotes. The problem doesn't happen using double quotes. @item $@{@var{var}=@var{expanded-value}@} @cindex $@{@var{var}=@var{expanded-value}@} On Ultrix, running @example default="yu,yaa" : $@{var="$default"@} @end example @noindent sets @var{var} to @samp{M-yM-uM-,M-yM-aM-a}, i.e., the 8th bit of each char is set. You don't observe the phenomenon using a simple @samp{echo $var} since apparently the shell resets the 8th bit when it expands $var. Here are two means to make this shell confess its sins: @example $ @kbd{cat -v < broken} $ @kbd{echo "`printf 'foo\r\n'`"" bar" | cmp - broken} - broken differ: char 4, line 1 @end example @item $(@var{commands}) @cindex $(@var{commands}) This construct is meant to replace @samp{`@var{commands}`}, and it has most of the problems listed under @code{`@var{commands}`}. This construct can be nested while this is impossible to do portably with back quotes. Unfortunately it is not yet universally supported. Most notably, even recent releases of Solaris don't support it: @example $ @kbd{showrev -c /bin/sh | grep version} Command version: SunOS 5.10 Generic 121004-01 Oct 2005 $ @kbd{echo $(echo blah)} syntax error: `(' unexpected @end example @noindent nor does @sc{irix} 6.5's Bourne shell: @example $ @kbd{uname -a} IRIX firebird-image 6.5 07151432 IP22 $ @kbd{echo $(echo blah)} $(echo blah) @end example If you do use @samp{$(@var{commands})}, make sure that the commands do not start with a parenthesis, as that would cause confusion with a different notation @samp{$((@var{expression}))} that in modern shells is an arithmetic expression not a command. To avoid the confusion, insert a space between the two opening parentheses. Avoid @var{commands} that contain unbalanced parentheses in here-documents, comments, or case statement patterns, as many shells mishandle them. For example, Bash 3.1, @samp{ksh88}, @command{pdksh} 5.2.14, and Zsh 4.2.6 all mishandle the following valid command: @example echo $(case x in x) echo hello;; esac) @end example @item ^ @cindex ^ quoting Always quote @samp{^}, otherwise traditional shells such as @command{/bin/sh} on Solaris 10 treat this like @samp{|}. @end table @node Assignments @section Assignments @cindex Shell assignments When setting several variables in a row, be aware that the order of the evaluation is undefined. For instance @samp{foo=1 foo=2; echo $foo} gives @samp{1} with Solaris @command{/bin/sh}, but @samp{2} with Bash. You must use @samp{;} to enforce the order: @samp{foo=1; foo=2; echo $foo}. Don't rely on the following to find @file{subdir/program}: @example PATH=subdir$PATH_SEPARATOR$PATH program @end example @noindent as this does not work with Zsh 3.0.6. Use something like this instead: @example (PATH=subdir$PATH_SEPARATOR$PATH; export PATH; exec program) @end example Don't rely on the exit status of an assignment: Ash 0.2 does not change the status and propagates that of the last statement: @example $ @kbd{false || foo=bar; echo $?} 1 $ @kbd{false || foo=`:`; echo $?} 0 @end example @noindent and to make things even worse, @acronym{QNX} 4.25 just sets the exit status to 0 in any case: @example $ @kbd{foo=`exit 1`; echo $?} 0 @end example To assign default values, follow this algorithm: @enumerate @item If the default value is a literal and does not contain any closing brace, use: @example : $@{var='my literal'@} @end example @item If the default value contains no closing brace, has to be expanded, and the variable being initialized is not intended to be IFS-split (i.e., it's not a list), then use: @example : $@{var="$default"@} @end example @item If the default value contains no closing brace, has to be expanded, and the variable being initialized is intended to be IFS-split (i.e., it's a list), then use: @example var=$@{var="$default"@} @end example @item If the default value contains a closing brace, then use: @example test "$@{var+set@}" = set || var="has a '@}'" @end example @end enumerate In most cases @samp{var=$@{var="$default"@}} is fine, but in case of doubt, just use the last form. @xref{Shell Substitutions}, items @samp{$@{@var{var}:-@var{value}@}} and @samp{$@{@var{var}=@var{value}@}} for the rationale. @node Parentheses @section Parentheses in Shell Scripts @cindex Shell parentheses Beware of two opening parentheses in a row, as some shell implementations mishandle them. For example, @samp{pdksh} 5.2.14 misparses the following code: @example if ((true) || false); then echo ok fi @end example @noindent To work around this problem, insert a space between the two opening parentheses. There is a similar problem and workaround with @samp{$((}; see @ref{Shell Substitutions}. Posix requires support for @code{case} patterns with opening parentheses like this: @example case $file_name in (*.c) echo "C source code";; esac @end example @noindent but the @code{(} in this example is not portable to many older Bourne shell implementations. It can be omitted safely. @node Slashes @section Slashes in Shell Scripts @cindex Shell slashes Unpatched Tru64 5.1 @command{sh} omits the last slash of command-line arguments that contain two trailing slashes: @example $ @kbd{echo / // /// //// .// //.} / / // /// ./ //. $ @kbd{x=//} $ @kbd{eval "echo \$x"} / $ @kbd{set -x} $ @kbd{echo abc | tr -t ab //} + echo abc + tr -t ab / /bc @end example Unpatched Tru64 4.0 @command{sh} adds a slash after @samp{"$var"} if the variable is empty and the second double-quote is followed by a word that begins and ends with slash: @example $ @kbd{sh -xc 'p=; echo "$p"/ouch/'} p= + echo //ouch/ //ouch/ @end example However, our understanding is that patches are available, so perhaps it's not worth worrying about working around these horrendous bugs. @node Special Shell Variables @section Special Shell Variables @cindex Shell variables @cindex Special shell variables Some shell variables should not be used, since they can have a deep influence on the behavior of the shell. In order to recover a sane behavior from the shell, some variables should be unset, but @command{unset} is not portable (@pxref{Limitations of Builtins}) and a fallback value is needed. As a general rule, shell variable names containing a lower-case letter are safe; you can define and use these variables without worrying about their effect on the underlying system, and without worrying about whether the shell changes them unexpectedly. (The exception is the shell variable @code{status}, as described below.) Here is a list of names that are known to cause trouble. This list is not exhaustive, but you should be safe if you avoid the name @code{status} and names containing only upper-case letters and underscores. @c Alphabetical order, case insensitive, `A' before `a'. @table @code @item _ Many shells reserve @samp{$_} for various purposes, e.g., the name of the last command executed. @item BIN_SH @evindex BIN_SH In Tru64, if @env{BIN_SH} is set to @code{xpg4}, subsidiary invocations of the standard shell conform to Posix. @item CDPATH @evindex CDPATH When this variable is set it specifies a list of directories to search when invoking @code{cd} with a relative file name that did not start with @samp{./} or @samp{../}. Posix 1003.1-2001 says that if a nonempty directory name from @env{CDPATH} is used successfully, @code{cd} prints the resulting absolute file name. Unfortunately this output can break idioms like @samp{abs=`cd src && pwd`} because @code{abs} receives the name twice. Also, many shells do not conform to this part of Posix; for example, @command{zsh} prints the result only if a directory name other than @file{.} was chosen from @env{CDPATH}. In practice the shells that have this problem also support @command{unset}, so you can work around the problem as follows: @example (unset CDPATH) >/dev/null 2>&1 && unset CDPATH @end example You can also avoid output by ensuring that your directory name is absolute or anchored at @samp{./}, as in @samp{abs=`cd ./src && pwd`}. Autoconf-generated scripts automatically unset @env{CDPATH} if possible, so you need not worry about this problem in those scripts. @item DUALCASE @evindex DUALCASE In the MKS shell, case statements and file name generation are case-insensitive unless @env{DUALCASE} is nonzero. Autoconf-generated scripts export this variable when they start up. @item ENV @itemx MAIL @itemx MAILPATH @itemx PS1 @itemx PS2 @itemx PS4 @evindex ENV @evindex MAIL @evindex MAILPATH @evindex PS1 @evindex PS2 @evindex PS4 These variables should not matter for shell scripts, since they are supposed to affect only interactive shells. However, at least one shell (the pre-3.0 @sc{uwin} Korn shell) gets confused about whether it is interactive, which means that (for example) a @env{PS1} with a side effect can unexpectedly modify @samp{$?}. To work around this bug, Autoconf-generated scripts do something like this: @example (unset ENV) >/dev/null 2>&1 && unset ENV MAIL MAILPATH PS1='$ ' PS2='> ' PS4='+ ' @end example @item IFS @evindex IFS Long ago, shell scripts inherited @env{IFS} from the environment, but this caused many problems so modern shells ignore any environment settings for @env{IFS}. Don't set the first character of @code{IFS} to backslash. Indeed, Bourne shells use the first character (backslash) when joining the components in @samp{"$@@"} and some shells then reinterpret (!)@: the backslash escapes, so you can end up with backspace and other strange characters. The proper value for @code{IFS} (in regular code, not when performing splits) is @samp{@key{SPC}@key{TAB}@key{RET}}. The first character is especially important, as it is used to join the arguments in @samp{$*}; however, note that traditional shells, but also bash-2.04, fail to adhere to this and join with a space anyway. @item LANG @itemx LC_ALL @itemx LC_COLLATE @itemx LC_CTYPE @itemx LC_MESSAGES @itemx LC_MONETARY @itemx LC_NUMERIC @itemx LC_TIME @evindex LANG @evindex LC_ALL @evindex LC_COLLATE @evindex LC_CTYPE @evindex LC_MESSAGES @evindex LC_MONETARY @evindex LC_NUMERIC @evindex LC_TIME Autoconf-generated scripts normally set all these variables to @samp{C} because so much configuration code assumes the C locale and Posix requires that locale environment variables be set to @samp{C} if the C locale is desired. However, some older, nonstandard systems (notably @acronym{SCO}) break if locale environment variables are set to @samp{C}, so when running on these systems Autoconf-generated scripts unset the variables instead. @item LANGUAGE @evindex LANGUAGE @env{LANGUAGE} is not specified by Posix, but it is a @acronym{GNU} extension that overrides @env{LC_ALL} in some cases, so Autoconf-generated scripts set it too. @item LC_ADDRESS @itemx LC_IDENTIFICATION @itemx LC_MEASUREMENT @itemx LC_NAME @itemx LC_PAPER @itemx LC_TELEPHONE @evindex LC_ADDRESS @evindex LC_IDENTIFICATION @evindex LC_MEASUREMENT @evindex LC_NAME @evindex LC_PAPER @evindex LC_TELEPHONE These locale environment variables are @acronym{GNU} extensions. They are treated like their Posix brethren (@env{LC_COLLATE}, etc.)@: as described above. @item LINENO Most modern shells provide the current line number in @code{LINENO}. Its value is the line number of the beginning of the current command. Autoconf attempts to execute @command{configure} with a shell that supports @code{LINENO}. If no such shell is available, it attempts to implement @code{LINENO} with a Sed prepass that replaces each instance of the string @code{$LINENO} (not followed by an alphanumeric character) with the line's number. You should not rely on @code{LINENO} within @command{eval}, as the behavior differs in practice. Also, the possibility of the Sed prepass means that you should not rely on @code{$LINENO} when quoted, when in here-documents, or when in long commands that cross line boundaries. Subshells should be OK, though. In the following example, lines 1, 6, and 9 are portable, but the other instances of @code{LINENO} are not: @example @group $ @kbd{cat lineno} echo 1. $LINENO cat < @kbd{ N} > @kbd{ s,$,-,} > @kbd{ t loop} > @kbd{ :loop} > @kbd{ s,^\([0-9]*\)\(.*\)[$]LINENO\([^a-zA-Z0-9_]\),\1\2\1\3,} > @kbd{ t loop} > @kbd{ s,-$,,} > @kbd{ s,^[0-9]*\n,,} > @kbd{ ' |} > @kbd{ sh} 1. 1 3. 3 4. 4 6. 6 7. 7 8. 8 9. 9 10. 10 @end group @end example @item NULLCMD @evindex NULLCMD When executing the command @samp{>foo}, @command{zsh} executes @samp{$NULLCMD >foo} unless it is operating in Bourne shell compatibility mode and the @command{zsh} version is newer than 3.1.6-dev-18. If you are using an older @command{zsh} and forget to set @env{NULLCMD}, your script might be suspended waiting for data on its standard input. @item PATH_SEPARATOR @evindex PATH_SEPARATOR On @acronym{DJGPP} systems, the @env{PATH_SEPARATOR} environment variable can be set to either @samp{:} or @samp{;} to control the path separator Bash uses to set up certain environment variables (such as @env{PATH}). You can set this variable to @samp{;} if you want @command{configure} to use @samp{;} as a separator; this might be useful if you plan to use non-Posix shells to execute files. @xref{File System Conventions}, for more information about @code{PATH_SEPARATOR}. @item PWD @evindex PWD Posix 1003.1-2001 requires that @command{cd} and @command{pwd} must update the @env{PWD} environment variable to point to the logical name of the current directory, but traditional shells do not support this. This can cause confusion if one shell instance maintains @env{PWD} but a subsidiary and different shell does not know about @env{PWD} and executes @command{cd}; in this case @env{PWD} points to the wrong directory. Use @samp{`pwd`} rather than @samp{$PWD}. @item RANDOM Many shells provide @code{RANDOM}, a variable that returns a different integer each time it is used. Most of the time, its value does not change when it is not used, but on @sc{irix} 6.5 the value changes all the time. This can be observed by using @command{set}. It is common practice to use @code{$RANDOM} as part of a file name, but code shouldn't rely on @code{$RANDOM} expanding to a nonempty string. @item status This variable is an alias to @samp{$?} for @code{zsh} (at least 3.1.6), hence read-only. Do not use it. @end table @node Limitations of Builtins @section Limitations of Shell Builtins @cindex Shell builtins @cindex Limitations of shell builtins No, no, we are serious: some shells do have limitations! :) You should always keep in mind that any builtin or command may support options, and therefore differ in behavior with arguments starting with a dash. For instance, the innocent @samp{echo "$word"} can give unexpected results when @code{word} starts with a dash. It is often possible to avoid this problem using @samp{echo "x$word"}, taking the @samp{x} into account later in the pipe. @table @asis @item @command{.} @prindex @command{.} Use @command{.} only with regular files (use @samp{test -f}). Bash 2.03, for instance, chokes on @samp{. /dev/null}. Also, remember that @command{.} uses @env{PATH} if its argument contains no slashes, so if you want to use @command{.} on a file @file{foo} in the current directory, you must use @samp{. ./foo}. @item @command{!} @prindex @command{!} The Unix version 7 shell did not support negating the exit status of commands with @command{!}, and this feature is still absent from some shells (e.g., Solaris @command{/bin/sh}). Shell code like this: @example if ! cmp file1 file2 >/dev/null 2>&1; then echo files differ or trouble fi @end example is therefore not portable in practice. Typically it is easy to rewrite such code, e.g.: @example cmp file1 file2 >/dev/null 2>&1 || echo files differ or trouble @end example More generally, one can always rewrite @samp{! @var{command}} as: @example if @var{command}; then (exit 1); else :; fi @end example @item @command{break} @c ------------------ @prindex @command{break} The use of @samp{break 2} etc.@: is safe. @item @command{case} @c ----------------- @prindex @command{case} You don't need to quote the argument; no splitting is performed. You don't need the final @samp{;;}, but you should use it. Because of a bug in its @code{fnmatch}, Bash fails to properly handle backslashes in character classes: @example bash-2.02$ @kbd{case /tmp in [/\\]*) echo OK;; esac} bash-2.02$ @end example @noindent This is extremely unfortunate, since you are likely to use this code to handle Posix or @sc{ms-dos} absolute file names. To work around this bug, always put the backslash first: @example bash-2.02$ @kbd{case '\TMP' in [\\/]*) echo OK;; esac} OK bash-2.02$ @kbd{case /tmp in [\\/]*) echo OK;; esac} OK @end example Many Bourne shells cannot handle closing brackets in character classes correctly. Some shells also have problems with backslash escaping in case you do not want to match the backslash: both a backslash and the escaped character match this pattern. To work around this, specify the character class in a variable, so that quote removal does not apply afterwards, and the special characters don't have to be backslash-escaped: @example $ @kbd{case '\' in [\<]) echo OK;; esac} OK $ @kbd{scanset='[<]'; case '\' in $scanset) echo OK;; esac} $ @end example Even with this, Solaris @command{ksh} matches a backslash if the set contains any of the characters @samp{|}, @samp{&}, @samp{(}, or @samp{)}. Conversely, Tru64 @command{ksh} (circa 2003) erroneously always matches a closing parenthesis if not specified in a character class: @example $ @kbd{case foo in *\)*) echo fail ;; esac} fail $ @kbd{case foo in *')'*) echo fail ;; esac} fail @end example Some shells, such as Ash 0.3.8, are confused by an empty @code{case}/@code{esac}: @example ash-0.3.8 $ @kbd{case foo in esac;} @error{}Syntax error: ";" unexpected (expecting ")") @end example Many shells still do not support parenthesized cases, which is a pity for those of us using tools that rely on balanced parentheses. For instance, Solaris @command{/bin/sh}: @example $ @kbd{case foo in (foo) echo foo;; esac} @error{}syntax error: `(' unexpected @end example @item @command{cd} @c --------------- @prindex @command{cd} Posix 1003.1-2001 requires that @command{cd} must support the @option{-L} (``logical'') and @option{-P} (``physical'') options, with @option{-L} being the default. However, traditional shells do not support these options, and their @command{cd} command has the @option{-P} behavior. Portable scripts should assume neither option is supported, and should assume neither behavior is the default. This can be a bit tricky, since the Posix default behavior means that, for example, @samp{ls ..} and @samp{cd ..} may refer to different directories if the current logical directory is a symbolic link. It is safe to use @command{cd @var{dir}} if @var{dir} contains no @file{..} components. Also, Autoconf-generated scripts check for this problem when computing variables like @code{ac_top_srcdir} (@pxref{Configuration Actions}), so it is safe to @command{cd} to these variables. See @xref{Special Shell Variables}, for portability problems involving @command{cd} and the @env{CDPATH} environment variable. Also please see the discussion of the @command{pwd} command. @item @command{echo} @c ----------------- @prindex @command{echo} The simple @command{echo} is probably the most surprising source of portability troubles. It is not possible to use @samp{echo} portably unless both options and escape sequences are omitted. New applications which are not aiming at portability should use @samp{printf} instead of @samp{echo}. Don't expect any option. @xref{Preset Output Variables}, @code{ECHO_N} etc.@: for a means to simulate @option{-n}. Do not use backslashes in the arguments, as there is no consensus on their handling. For @samp{echo '\n' | wc -l}, the @command{sh} of Solaris outputs 2, but Bash and Zsh (in @command{sh} emulation mode) output 1. The problem is truly @command{echo}: all the shells understand @samp{'\n'} as the string composed of a backslash and an @samp{n}. Because of these problems, do not pass a string containing arbitrary characters to @command{echo}. For example, @samp{echo "$foo"} is safe if you know that @var{foo}'s value cannot contain backslashes and cannot start with @samp{-}, but otherwise you should use a here-document like this: @example cat </dev/null 2>&1 && @var{action} @end example @noindent Use @code{case} where possible since it is faster, being a shell builtin: @example case $ac_feature in *[!-a-zA-Z0-9_]*) @var{action};; esac @end example Alas, negated character classes are probably not portable, although no shell is known to not support the Posix syntax @samp{[!@dots{}]} (when in interactive mode, @command{zsh} is confused by the @samp{[!@dots{}]} syntax and looks for an event in its history because of @samp{!}). Many shells do not support the alternative syntax @samp{[^@dots{}]} (Solaris, Digital Unix, etc.). One solution can be: @example expr "$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null && @var{action} @end example @noindent or better yet @example expr "X$ac_feature" : '.*[^-a-zA-Z0-9_]' >/dev/null && @var{action} @end example @samp{expr "X@var{foo}" : "X@var{bar}"} is more robust than @samp{echo "X@var{foo}" | grep "^X@var{bar}"}, because it avoids problems when @samp{@var{foo}} contains backslashes. @item @command{trap} @c ----------------- @prindex @command{trap} It is safe to trap at least the signals 1, 2, 13, and 15. You can also trap 0, i.e., have the @command{trap} run when the script ends (either via an explicit @command{exit}, or the end of the script). The trap for 0 should be installed outside of a shell function, or @acronym{AIX} 5.3 @command{/bin/sh} will invoke the trap at the end of this function. Posix says that @samp{trap - 1 2 13 15} resets the traps for the specified signals to their default values, but many common shells (e.g., Solaris @command{/bin/sh}) misinterpret this and attempt to execute a ``command'' named @command{-} when the specified conditions arise. There is no portable workaround, except for @samp{trap - 0}, for which @samp{trap '' 0} is a portable substitute. Although Posix is not absolutely clear on this point, it is widely admitted that when entering the trap @samp{$?} should be set to the exit status of the last command run before the trap. The ambiguity can be summarized as: ``when the trap is launched by an @command{exit}, what is the @emph{last} command run: that before @command{exit}, or @command{exit} itself?'' Bash considers @command{exit} to be the last command, while Zsh and Solaris @command{/bin/sh} consider that when the trap is run it is @emph{still} in the @command{exit}, hence it is the previous exit status that the trap receives: @example $ @kbd{cat trap.sh} trap 'echo $?' 0 (exit 42); exit 0 $ @kbd{zsh trap.sh} 42 $ @kbd{bash trap.sh} 0 @end example The portable solution is then simple: when you want to @samp{exit 42}, run @samp{(exit 42); exit 42}, the first @command{exit} being used to set the exit status to 42 for Zsh, and the second to trigger the trap and pass 42 as exit status for Bash. The shell in Free@acronym{BSD} 4.0 has the following bug: @samp{$?} is reset to 0 by empty lines if the code is inside @command{trap}. @example $ @kbd{trap 'false} echo $?' 0 $ @kbd{exit} 0 @end example @noindent Fortunately, this bug only affects @command{trap}. @item @command{true} @c ----------------- @prindex @command{true} @c Info cannot handle `:' in index entries. @c @prindex @command{:} Don't worry: as far as we know @command{true} is portable. Nevertheless, it's not always a builtin (e.g., Bash 1.x), and the portable shell community tends to prefer using @command{:}. This has a funny side effect: when asked whether @command{false} is more portable than @command{true} Alexandre Oliva answered: @quotation In a sense, yes, because if it doesn't exist, the shell will produce an exit status of failure, which is correct for @command{false}, but not for @command{true}. @end quotation @item @command{unset} @c ------------------ @prindex @command{unset} In some nonconforming shells (e.g., Bash 2.05a), @code{unset FOO} fails when @code{FOO} is not set. Also, Bash 2.01 mishandles @code{unset MAIL} in some cases and dumps core. A few ancient shells lack @command{unset} entirely. Nevertheless, because it is extremely useful to disable embarrassing variables such as @code{PS1}, you can test for its existence and use it @emph{provided} you give a neutralizing value when @command{unset} is not supported: @smallexample # "|| exit" suppresses any "Segmentation fault" message. if ( (MAIL=60; unset MAIL) || exit) >/dev/null 2>&1; then unset=unset else unset=false fi $unset PS1 || PS1='$ ' @end smallexample @noindent @xref{Special Shell Variables}, for some neutralizing values. Also, see @ref{Limitations of Builtins}, documentation of @command{export}, for the case of environment variables. @end table @node Limitations of Usual Tools @section Limitations of Usual Tools @cindex Limitations of usual tools The small set of tools you can expect to find on any machine can still include some limitations you should be aware of. @table @asis @item Awk @c ------ @prindex Awk Don't leave white space before the opening parenthesis in a user function call. Posix does not allow this and @acronym{GNU} Awk rejects it: @example $ @kbd{gawk 'function die () @{ print "Aaaaarg!" @} BEGIN @{ die () @}'} gawk: cmd. line:2: BEGIN @{ die () @} gawk: cmd. line:2: ^ parse error $ @kbd{gawk 'function die () @{ print "Aaaaarg!" @} BEGIN @{ die() @}'} Aaaaarg! @end example If you want your program to be deterministic, don't depend on @code{for} on arrays: @example $ @kbd{cat for.awk} END @{ arr["foo"] = 1 arr["bar"] = 1 for (i in arr) print i @} $ @kbd{gawk -f for.awk printf "foo\n|foo\n" | $EGREP '^(|foo|bar)$' |foo > printf "bar\nbar|\n" | $EGREP '^(foo|bar|)$' bar| > printf "foo\nfoo|\n|bar\nbar\n" | $EGREP '^(foo||bar)$' foo |bar @end example @command{$EGREP} also suffers the limitations of @command{grep}. @item @command{expr} @c ----------------- @prindex @command{expr} No @command{expr} keyword starts with @samp{X}, so use @samp{expr X"@var{word}" : 'X@var{regex}'} to keep @command{expr} from misinterpreting @var{word}. Don't use @code{length}, @code{substr}, @code{match} and @code{index}. @item @command{expr} (@samp{|}) @prindex @command{expr} (@samp{|}) You can use @samp{|}. Although Posix does require that @samp{expr ''} return the empty string, it does not specify the result when you @samp{|} together the empty string (or zero) with the empty string. For example: @example expr '' \| '' @end example Posix 1003.2-1992 returns the empty string for this case, but traditional Unix returns @samp{0} (Solaris is one such example). In Posix 1003.1-2001, the specification was changed to match traditional Unix's behavior (which is bizarre, but it's too late to fix this). Please note that the same problem does arise when the empty string results from a computation, as in: @example expr bar : foo \| foo : bar @end example @noindent Avoid this portability problem by avoiding the empty string. @item @command{expr} (@samp{:}) @c ---------------------------- @prindex @command{expr} Portable @command{expr} regular expressions should use @samp{\} to escape only characters in the string @samp{$()*.0123456789[\^n@{@}}. For example, alternation, @samp{\|}, is common but Posix does not require its support, so it should be avoided in portable scripts. Similarly, @samp{\+} and @samp{\?} should be avoided. Portable @command{expr} regular expressions should not begin with @samp{^}. Patterns are automatically anchored so leading @samp{^} is not needed anyway. The Posix standard is ambiguous as to whether @samp{expr 'a' : '\(b\)'} outputs @samp{0} or the empty string. In practice, it outputs the empty string on most platforms, but portable scripts should not assume this. For instance, the @acronym{QNX} 4.25 native @command{expr} returns @samp{0}. One might think that a way to get a uniform behavior would be to use the empty string as a default value: @example expr a : '\(b\)' \| '' @end example @noindent Unfortunately this behaves exactly as the original expression; see the @command{expr} (@samp{|}) entry for more information. Ancient @command{expr} implementations (e.g., SunOS 4 @command{expr} and Solaris 8 @command{/usr/ucb/expr}) have a silly length limit that causes @command{expr} to fail if the matched substring is longer than 120 bytes. In this case, you might want to fall back on @samp{echo|sed} if @command{expr} fails. Nowadays this is of practical importance only for the rare installer who mistakenly puts @file{/usr/ucb} before @file{/usr/bin} in @env{PATH}. On Mac OS X 10.4, @command{expr} mishandles the pattern @samp{[^-]} in some cases. For example, the command @example expr Xpowerpc-apple-darwin8.1.0 : 'X[^-]*-[^-]*-\(.*\)' @end example @noindent outputs @samp{apple-darwin8.1.0} rather than the correct @samp{darwin8.1.0}. This particular case can be worked around by substituting @samp{[^--]} for @samp{[^-]}. Don't leave, there is some more! The @acronym{QNX} 4.25 @command{expr}, in addition of preferring @samp{0} to the empty string, has a funny behavior in its exit status: it's always 1 when parentheses are used! @example $ @kbd{val=`expr 'a' : 'a'`; echo "$?: $val"} 0: 1 $ @kbd{val=`expr 'a' : 'b'`; echo "$?: $val"} 1: 0 $ @kbd{val=`expr 'a' : '\(a\)'`; echo "?: $val"} 1: a $ @kbd{val=`expr 'a' : '\(b\)'`; echo "?: $val"} 1: 0 @end example @noindent In practice this can be a big problem if you are ready to catch failures of @command{expr} programs with some other method (such as using @command{sed}), since you may get twice the result. For instance @example $ @kbd{expr 'a' : '\(a\)' || echo 'a' | sed 's/^\(a\)$/\1/'} @end example @noindent outputs @samp{a} on most hosts, but @samp{aa} on @acronym{QNX} 4.25. A simple workaround consists of testing @command{expr} and using a variable set to @command{expr} or to @command{false} according to the result. Tru64 @command{expr} incorrectly treats the result as a number, if it can be interpreted that way: @example $ @kbd{expr 00001 : '.*\(...\)'} 1 @end example @item @command{fgrep} @c ------------------ @prindex @command{fgrep} Posix 1003.1-2001 no longer requires @command{fgrep}, but many older hosts do not yet support the Posix replacement @code{grep -F}. Also, some traditional implementations do not work on long input lines. To work around these problems, invoke @code{AC_PROG_FGREP} and then use @code{$FGREP}. @item @command{find} @c ----------------- @prindex @command{find} The option @option{-maxdepth} seems to be @acronym{GNU} specific. Tru64 v5.1, Net@acronym{BSD} 1.5 and Solaris @command{find} commands do not understand it. The replacement of @samp{@{@}} is guaranteed only if the argument is exactly @emph{@{@}}, not if it's only a part of an argument. For instance on DU, and @acronym{HP-UX} 10.20 and @acronym{HP-UX} 11: @example $ @kbd{touch foo} $ @kbd{find . -name foo -exec echo "@{@}-@{@}" \;} @{@}-@{@} @end example @noindent while @acronym{GNU} @command{find} reports @samp{./foo-./foo}. @item @command{grep} @c ----------------- @prindex @command{grep} Portable scripts can rely on the @command{grep} options @option{-c}, @option{-l}, @option{-n}, and @option{-v}, but should avoid other options. For example, don't use @option{-w}, as Posix does not require it and Irix 6.5.16m's @command{grep} does not support it. Also, portable scripts should not combine @option{-c} with @option{-l}, as Posix does not allow this. Some of the options required by Posix are not portable in practice. Don't use @samp{grep -q} to suppress output, because many @command{grep} implementations (e.g., Solaris) do not support @option{-q}. Don't use @samp{grep -s} to suppress output either, because Posix says @option{-s} does not suppress output, only some error messages; also, the @option{-s} option of traditional @command{grep} behaved like @option{-q} does in most modern implementations. Instead, redirect the standard output and standard error (in case the file doesn't exist) of @code{grep} to @file{/dev/null}. Check the exit status of @code{grep} to determine whether it found a match. Some traditional @command{grep} implementations do not work on long input lines. On AIX the default @code{grep} silently truncates long lines on the input before matching. Also, many implementations do not support multiple regexps with @option{-e}: they either reject @option{-e} entirely (e.g., Solaris) or honor only the last pattern (e.g., @acronym{IRIX} 6.5 and NeXT). To work around these problems, invoke @code{AC_PROG_GREP} and then use @code{$GREP}. Another possible workaround for the multiple @option{-e} problem is to separate the patterns by newlines, for example: @example grep 'foo bar' in.txt @end example @noindent except that this fails with traditional @command{grep} implementations and with Open@acronym{BSD} 3.8 @command{grep}. Traditional @command{grep} implementations (e.g., Solaris) do not support the @option{-E} or @option{-F} options. To work around these problems, invoke @code{AC_PROG_EGREP} and then use @code{$EGREP}, and similarly for @code{AC_PROG_FGREP} and @code{$FGREP}. Even if you are willing to require support for Posix @command{grep}, your script should not use both @option{-E} and @option{-F}, since Posix does not allow this combination. Portable @command{grep} regular expressions should use @samp{\} only to escape characters in the string @samp{$()*.0123456789[\^@{@}}. For example, alternation, @samp{\|}, is common but Posix does not require its support in basic regular expressions, so it should be avoided in portable scripts. Solaris @command{grep} does not support it. Similarly, @samp{\+} and @samp{\?} should be avoided. @item @command{join} @c ----------------- @prindex @command{join} Solaris 8 @command{join} has bugs when the second operand is standard input, and when standard input is a pipe. For example, the following shell script causes Solaris 8 @command{join} to loop forever: @example cat >file <<'EOF' 1 x 2 y EOF cat file | join file - @end example Use @samp{join - file} instead. @item @command{ln} @c --------------- @prindex @command{ln} @cindex Symbolic links Don't rely on @command{ln} having a @option{-f} option. Symbolic links are not available on old systems; use @samp{$(LN_S)} as a portable substitute. For versions of the @acronym{DJGPP} before 2.04, @command{ln} emulates symbolic links to executables by generating a stub that in turn calls the real program. This feature also works with nonexistent files like in the Posix spec. So @samp{ln -s file link} generates @file{link.exe}, which attempts to call @file{file.exe} if run. But this feature only works for executables, so @samp{cp -p} is used instead for these systems. @acronym{DJGPP} versions 2.04 and later have full support for symbolic links. @item @command{ls} @c --------------- @prindex @command{ls} @cindex Listing directories The portable options are @option{-acdilrtu}. Current practice is for @option{-l} to output both owner and group, even though ancient versions of @command{ls} omitted the group. On ancient hosts, @samp{ls foo} sent the diagnostic @samp{foo not found} to standard output if @file{foo} did not exist. Hence a shell command like @samp{sources=`ls *.c 2>/dev/null`} did not always work, since it was equivalent to @samp{sources='*.c not found'} in the absence of @samp{.c} files. This is no longer a practical problem, since current @command{ls} implementations send diagnostics to standard error. @item @command{mkdir} @c ------------------ @prindex @command{mkdir} @cindex Making directories No @command{mkdir} option is portable to older systems. Instead of @samp{mkdir -p @var{file-name}}, you should use @code{AS_MKDIR_P(@var{file-name})} (@pxref{Programming in M4sh}) or @code{AC_PROG_MKDIR_P} (@pxref{Particular Programs}). Combining the @option{-m} and @option{-p} options, as in @samp{mkdir -m go-w -p @var{dir}}, often leads to trouble. Free@acronym{BSD} @command{mkdir} incorrectly attempts to change the permissions of @var{dir} even if it already exists. @acronym{HP-UX} 11.23 and @acronym{IRIX} 6.5 @command{mkdir} often assign the wrong permissions to any newly-created parents of @var{dir}. Posix does not clearly specify whether @samp{mkdir -p foo} should succeed when @file{foo} is a symbolic link to an already-existing directory. The @acronym{GNU} Core Utilities 5.1.0 @command{mkdir} succeeds, but Solaris @command{mkdir} fails. Traditional @code{mkdir -p} implementations suffer from race conditions. For example, if you invoke @code{mkdir -p a/b} and @code{mkdir -p a/c} at the same time, both processes might detect that @file{a} is missing, one might create @file{a}, then the other might try to create @file{a} and fail with a @code{File exists} diagnostic. The @acronym{GNU} Core Utilities (@samp{fileutils} version 4.1), Free@acronym{BSD} 5.0, Net@acronym{BSD} 2.0.2, and Open@acronym{BSD} 2.4 are known to be race-free when two processes invoke @code{mkdir -p} simultaneously, but earlier versions are vulnerable. Solaris @command{mkdir} is still vulnerable as of Solaris 10, and other traditional Unix systems are probably vulnerable too. This possible race is harmful in parallel builds when several Make rules call @code{mkdir -p} to construct directories. You may use @code{install-sh -d} as a safe replacement, provided this script is recent enough; the copy shipped with Autoconf 2.60 and Automake 1.10 is OK, but copies from older versions are vulnerable. @item @command{mktemp} @c ------------------- @prindex @command{mktemp} @cindex Creating temporary files Shell scripts can use temporary files safely with @command{mktemp}, but it does not exist on all systems. A portable way to create a safe temporary file name is to create a temporary directory with mode 700 and use a file inside this directory. Both methods prevent attackers from gaining control, though @command{mktemp} is far less likely to fail gratuitously under attack. Here is sample code to create a new temporary directory safely: @example # Create a temporary directory $tmp in $TMPDIR (default /tmp). # Use mktemp if possible; otherwise fall back on mkdir, # with $RANDOM to make collisions less likely. : $@{TMPDIR=/tmp@} @{ tmp=` (umask 077 && mktemp -d "$TMPDIR/fooXXXXXX") 2>/dev/null ` && test -n "$tmp" && test -d "$tmp" @} || @{ tmp=$TMPDIR/foo$$-$RANDOM (umask 077 && mkdir "$tmp") @} || exit $? @end example @item @command{mv} @c --------------- @prindex @command{mv} @cindex Moving open files The only portable options are @option{-f} and @option{-i}. Moving individual files between file systems is portable (it was in Unix version 6), but it is not always atomic: when doing @samp{mv new existing}, there's a critical section where neither the old nor the new version of @file{existing} actually exists. On some systems moving files from @file{/tmp} can sometimes cause undesirable (but perfectly valid) warnings, even if you created these files. This is because @file{/tmp} belongs to a group that ordinary users are not members of, and files created in @file{/tmp} inherit the group of @file{/tmp}. When the file is copied, @command{mv} issues a diagnostic without failing: @smallexample $ @kbd{touch /tmp/foo} $ @kbd{mv /tmp/foo .} @error{}mv: ./foo: set owner/group (was: 100/0): Operation not permitted $ @kbd{echo $?} 0 $ @kbd{ls foo} foo @end smallexample @noindent This annoying behavior conforms to Posix, unfortunately. Moving directories across mount points is not portable, use @command{cp} and @command{rm}. @acronym{DOS} variants cannot rename or remove open files, and do not support commands like @samp{mv foo bar >foo}, even though this is perfectly portable among Posix hosts. @item @command{od} @c --------------- @prindex @command{od} In Mac OS X 10.3, @command{od} does not support the standard Posix options @option{-A}, @option{-j}, @option{-N}, or @option{-t}, or the @acronym{XSI} option @option{-s}. The only supported Posix option is @option{-v}, and the only supported @acronym{XSI} options are those in @option{-bcdox}. The @acronym{BSD} @command{hexdump} program can be used instead. This problem no longer exists in Mac OS X 10.4.3. @item @command{rm} @c --------------- @prindex @command{rm} The @option{-f} and @option{-r} options are portable. It is not portable to invoke @command{rm} without operands. For example, on many systems @samp{rm -f -r} (with no other arguments) silently succeeds without doing anything, but it fails with a diagnostic on Net@acronym{BSD} 2.0.2. A file might not be removed even if its parent directory is writable and searchable. Many Posix hosts cannot remove a mount point, a named stream, a working directory, or a last link to a file that is being executed. @acronym{DOS} variants cannot rename or remove open files, and do not support commands like @samp{rm foo >foo}, even though this is perfectly portable among Posix hosts. @item @command{sed} @c ---------------- @prindex @command{sed} Patterns should not include the separator (unless escaped), even as part of a character class. In conformance with Posix, the Cray @command{sed} rejects @samp{s/[^/]*$//}: use @samp{s,[^/]*$,,}. Avoid empty patterns within parentheses (i.e., @samp{\(\)}). Posix does not require support for empty patterns, and Unicos 9 @command{sed} rejects them. Unicos 9 @command{sed} loops endlessly on patterns like @samp{.*\n.*}. Sed scripts should not use branch labels longer than 8 characters and should not contain comments. @acronym{HP-UX} sed has a limit of 99 commands (not counting @samp{:} commands) and 48 labels, which can not be circumvented by using more than one script file. It can execute up to 19 reads with the @samp{r} command per cycle. Solaris @command{/usr/ucb/sed} rejects usages that exceed an limit of about 6000 bytes for the internal representation of commands. Avoid redundant @samp{;}, as some @command{sed} implementations, such as Net@acronym{BSD} 1.4.2's, incorrectly try to interpret the second @samp{;} as a command: @example $ @kbd{echo a | sed 's/x/x/;;s/x/x/'} sed: 1: "s/x/x/;;s/x/x/": invalid command code ; @end example Input should not have unreasonably long lines, since some @command{sed} implementations have an input buffer limited to 4000 bytes. Portable @command{sed} regular expressions should use @samp{\} only to escape characters in the string @samp{$()*.0123456789[\^n@{@}}. For example, alternation, @samp{\|}, is common but Posix does not require its support, so it should be avoided in portable scripts. Solaris @command{sed} does not support alternation; e.g., @samp{sed '/a\|b/d'} deletes only lines that contain the literal string @samp{a|b}. Similarly, @samp{\+} and @samp{\?} should be avoided. Anchors (@samp{^} and @samp{$}) inside groups are not portable. Nested parenthesization in patterns (e.g., @samp{\(\(a*\)b*)\)}) is quite portable to current hosts, but was not supported by some ancient @command{sed} implementations like SVR3. Some @command{sed} implementations, e.g., Solaris, restrict the special role of the asterisk to one-character regular expressions. This may lead to unexpected behavior: @example $ @kbd{echo '1*23*4' | /usr/bin/sed 's/\(.\)*/x/g'} x2x4 $ @kbd{echo '1*23*4' | /usr/xpg4/bin/sed 's/\(.\)*/x/g'} x @end example The @option{-e} option is portable, so long as its argument does not begin with @samp{a}, @samp{c}, or @samp{i} (as this runs afoul of a Tru64 5.1 bug). Some people prefer to use @samp{-e}: @example sed -e '@var{command-1}' \ -e '@var{command-2}' @end example @noindent as opposed to the equivalent: @example sed ' @var{command-1} @var{command-2} ' @end example @noindent The following usage is sometimes equivalent: @example sed '@var{command-1};@var{command-2}' @end example but Posix says that this use of a semicolon has undefined effect if @var{command-1}'s verb is @samp{@{}, @samp{a}, @samp{b}, @samp{c}, @samp{i}, @samp{r}, @samp{t}, @samp{w}, @samp{:}, or @samp{#}, so you should use semicolon only with simple scripts that do not use these verbs. Commands inside @{ @} brackets are further restricted. Posix says that they cannot be preceded by addresses, @samp{!}, or @samp{;}, and that each command must be followed immediately by a newline, without any intervening blanks or semicolons. The closing bracket must be alone on a line, other than white space preceding or following it. Contrary to yet another urban legend, you may portably use @samp{&} in the replacement part of the @code{s} command to mean ``what was matched''. All descendants of Unix version 7 @command{sed} (at least; we don't have first hand experience with older @command{sed} implementations) have supported it. Posix requires that you must not have any white space between @samp{!} and the following command. It is OK to have blanks between the address and the @samp{!}. For instance, on Solaris: @example $ @kbd{echo "foo" | sed -n '/bar/ ! p'} @error{}Unrecognized command: /bar/ ! p $ @kbd{echo "foo" | sed -n '/bar/! p'} @error{}Unrecognized command: /bar/! p $ @kbd{echo "foo" | sed -n '/bar/ !p'} foo @end example Posix also says that you should not combine @samp{!} and @samp{;}. If you use @samp{!}, it is best to put it on a command that is delimited by newlines rather than @samp{;}. Also note that Posix requires that the @samp{b}, @samp{t}, @samp{r}, and @samp{w} commands be followed by exactly one space before their argument. On the other hand, no white space is allowed between @samp{:} and the subsequent label name. If a sed script is specified on the command line and ends in an @samp{a}, @samp{c}, or @samp{i} command, the last line of inserted text should be followed by a newline. Otherwise some @command{sed} implementations (e.g., Open@acronym{BSD} 3.9) do not append a newline to the inserted text. Many @command{sed} implementations (e.g., MacOS X 10.4, Open@acronym{BSD} 3.9, Solaris 10 @command{/usr/ucb/sed}) strip leading white space from the text of @samp{a}, @samp{c}, and @samp{i} commands. Prepend a backslash to work around this incompatibility with Posix: @example $ @kbd{echo flushleft | sed 'a\} > @kbd{ indented} > @kbd{'} flushleft indented $ @kbd{echo foo | sed 'a\} > @kbd{\ indented} > @kbd{'} flushleft indented @end example @item @command{sed} (@samp{t}) @c --------------------------- @prindex @command{sed} (@samp{t}) Some old systems have @command{sed} that ``forget'' to reset their @samp{t} flag when starting a new cycle. For instance on @acronym{MIPS RISC/OS}, and on @sc{irix} 5.3, if you run the following @command{sed} script (the line numbers are not actual part of the texts): @example s/keep me/kept/g # a t end # b s/.*/deleted/g # c :end # d @end example @noindent on @example delete me # 1 delete me # 2 keep me # 3 delete me # 4 @end example @noindent you get @example deleted delete me kept deleted @end example @noindent instead of @example deleted deleted kept deleted @end example Why? When processing line 1, (c) matches, therefore sets the @samp{t} flag, and the output is produced. When processing line 2, the @samp{t} flag is still set (this is the bug). Command (a) fails to match, but @command{sed} is not supposed to clear the @samp{t} flag when a substitution fails. Command (b) sees that the flag is set, therefore it clears it, and jumps to (d), hence you get @samp{delete me} instead of @samp{deleted}. When processing line (3), @samp{t} is clear, (a) matches, so the flag is set, hence (b) clears the flags and jumps. Finally, since the flag is clear, line 4 is processed properly. There are two things one should remember about @samp{t} in @command{sed}. Firstly, always remember that @samp{t} jumps if @emph{some} substitution succeeded, not only the immediately preceding substitution. Therefore, always use a fake @samp{t clear} followed by a @samp{:clear} on the next line, to reset the @samp{t} flag where needed. Secondly, you cannot rely on @command{sed} to clear the flag at each new cycle. One portable implementation of the script above is: @example t clear :clear s/keep me/kept/g t end s/.*/deleted/g :end @end example @item @command{touch} @c ------------------ @prindex @command{touch} @cindex timestamp resolution If you specify the desired timestamp (e.g., with the @option{-r} option), @command{touch} typically uses the @code{utime} or @code{utimes} system call, which can result in the same kind of timestamp truncation problems that @samp{cp -p} has. On ancient @acronym{BSD} systems, @command{touch} or any command that results in an empty file does not update the timestamps, so use a command like @command{echo} as a workaround. Also, @acronym{GNU} @command{touch} 3.16r (and presumably all before that) fails to work on SunOS 4.1.3 when the empty file is on an @acronym{NFS}-mounted 4.2 volume. However, these problems are no longer of practical concern. @end table @node Portable Make @chapter Portable Make Programming @prindex @command{make} @cindex Limitations of @command{make} Writing portable makefiles is an art. Since a makefile's commands are executed by the shell, you must consider the shell portability issues already mentioned. However, other issues are specific to @command{make} itself. @menu * $< in Ordinary Make Rules:: $< in ordinary rules * Failure in Make Rules:: Failing portably in rules * Special Chars in Names:: Special Characters in Macro Names * Backslash-Newline-Newline:: Empty last lines in macro definitions * Backslash-Newline Comments:: Spanning comments across line boundaries * Long Lines in Makefiles:: Line length limitations * Macros and Submakes:: @code{make macro=value} and submakes * The Make Macro MAKEFLAGS:: @code{$(MAKEFLAGS)} portability issues * The Make Macro SHELL:: @code{$(SHELL)} portability issues * Comments in Make Rules:: Other problems with Make comments * obj/ and Make:: Don't name a subdirectory @file{obj} * make -k Status:: Exit status of @samp{make -k} * VPATH and Make:: @code{VPATH} woes * Single Suffix Rules:: Single suffix rules and separated dependencies * Timestamps and Make:: Subsecond timestamp resolution @end menu @node $< in Ordinary Make Rules @section @code{$<} in Ordinary Make Rules Posix says that the @samp{$<} construct in makefiles can be used only in inference rules and in the @samp{.DEFAULT} rule; its meaning in ordinary rules is unspecified. Solaris @command{make} for instance replaces it with the empty string. Open@acronym{BSD} (3.0 and later) @command{make} diagnoses these uses and errors out. @node Failure in Make Rules @section Failure in Make Rules Since 1992 Posix has required that @command{make} must invoke each command with the equivalent of a @samp{sh -c} subshell. However, many @command{make} implementations, including @acronym{BSD} make through 2004, use @samp{sh -e -c} instead, and the @option{-e} option causes the subshell to exit immediately if a subsidiary simple-command fails. For example, the command @samp{touch T; rm -f U} always attempts to remove @file{U} with Posix make, but incompatible @command{make} implementations skip the @command{rm} if the @command{touch} fails. One way to work around this is to reword the affected simple-commands so that they always succeed, e.g., @samp{touch T || :; rm -f U}. However, even this approach can run into common bugs in @acronym{BSD} implementations of the @option{-e} option of @command{sh} and @command{set} (@pxref{Limitations of Builtins}), so if you are worried about porting to buggy @acronym{BSD} shells it may be simpler to migrate complicated @command{make} actions into separate scripts. @node Special Chars in Names @section Special Characters in Make Macro Names Posix limits macro names to nonempty strings containing only @acronym{ASCII} letters and digits, @samp{.}, and @samp{_}. Many @command{make} implementations allow a wider variety of characters, but portable makefiles should avoid them. It is portable to start a name with a special character, e.g., @samp{$(.FOO)}. Some ancient @command{make} implementations don't support leading underscores in macro names. An example is @acronym{NEWS-OS} 4.2R. @example $ @kbd{cat Makefile} _am_include = # _am_quote = all:; @@echo this is test $ @kbd{make} Make: Must be a separator on rules line 2. Stop. $ @kbd{cat Makefile2} am_include = # am_quote = all:; @@echo this is test $ @kbd{make -f Makefile2} this is test @end example @noindent However, this problem is no longer of practical concern. @node Backslash-Newline-Newline @section Backslash-Newline-Newline in Make Macro Values @c This has been seen on ia64 hpux 11.20, and on one hppa hpux 10.20, @c but another hppa hpux 10.20 didn't have it. Bob Proulx @c thinks it was in hpux 8.0 too. On some versions of @acronym{HP-UX}, @command{make} reads multiple newlines following a backslash, continuing to the next non-empty line. For example, @example FOO = one \ BAR = two test: : FOO is "$(FOO)" : BAR is "$(BAR)" @end example @noindent shows @code{FOO} equal to @code{one BAR = two}. Other implementations sensibly let a backslash continue only to the immediately following line. @node Backslash-Newline Comments @section Backslash-Newline in Make Comments According to Posix, Make comments start with @code{#} and continue until an unescaped newline is reached. @example $ @kbd{cat Makefile} # A = foo \ bar \ baz all: @@echo ok $ @kbd{make} # GNU make ok @end example @noindent However this is not always the case. Some implementations discard everything from @code{#} through the end of the line, ignoring any trailing backslash. @example $ @kbd{pmake} # BSD make "Makefile", line 3: Need an operator Fatal errors encountered -- cannot continue @end example @noindent Therefore, if you want to comment out a multi-line definition, prefix each line with @code{#}, not only the first. @example # A = foo \ # bar \ # baz @end example @node Long Lines in Makefiles @section Long Lines in Makefiles Tru64 5.1's @command{make} has been reported to crash when given a makefile with lines longer than around 20 kB. Earlier versions are reported to exit with @code{Line too long} diagnostics. @node Macros and Submakes @section @code{make macro=value} and Submakes A command-line variable definition such as @code{foo=bar} overrides any definition of @code{foo} in a makefile. Some @command{make} implementations (such as @acronym{GNU} @command{make}) propagate this override to subsidiary invocations of @command{make}. Some other implementations do not pass the substitution along to submakes. @example $ @kbd{cat Makefile} foo = foo one: @@echo $(foo) $(MAKE) two two: @@echo $(foo) $ @kbd{make foo=bar} # GNU make 3.79.1 bar make two make[1]: Entering directory `/home/adl' bar make[1]: Leaving directory `/home/adl' $ @kbd{pmake foo=bar} # BSD make bar pmake two foo @end example You have a few possibilities if you do want the @code{foo=bar} override to propagate to submakes. One is to use the @option{-e} option, which causes all environment variables to have precedence over the makefile macro definitions, and declare foo as an environment variable: @example $ @kbd{env foo=bar make -e} @end example The @option{-e} option is propagated to submakes automatically, and since the environment is inherited between @command{make} invocations, the @code{foo} macro is overridden in submakes as expected. This syntax (@code{foo=bar make -e}) is portable only when used outside of a makefile, for instance from a script or from the command line. When run inside a @command{make} rule, @acronym{GNU} @command{make} 3.80 and prior versions forget to propagate the @option{-e} option to submakes. Moreover, using @option{-e} could have unexpected side effects if your environment contains some other macros usually defined by the makefile. (See also the note about @code{make -e} and @code{SHELL} below.) Another way to propagate overrides to submakes is to do it manually, from your makefile: @example foo = foo one: @@echo $(foo) $(MAKE) foo=$(foo) two two: @@echo $(foo) @end example You need to foresee all macros that a user might want to override if you do that. @node The Make Macro MAKEFLAGS @section The Make Macro MAKEFLAGS @cindex @code{MAKEFLAGS} and @command{make} @cindex @command{make} and @code{MAKEFLAGS} Posix requires @command{make} to use @code{MAKEFLAGS} to affect the current and recursive invocations of make, but allows implementations several formats for the variable. It is tricky to parse @code{$MAKEFLAGS} to determine whether @option{-s} for silent execution or @option{-k} for continued execution are in effect. For example, you cannot assume that the first space-separated word in @code{$MAKEFLAGS} contains single-letter options, since in the Cygwin version of @acronym{GNU} @command{make} it is either @option{--unix} or @option{--win32} with the second word containing single-letter options. @example $ @kbd{cat Makefile} all: @@echo MAKEFLAGS = $(MAKEFLAGS) $ @kbd{make} MAKEFLAGS = --unix $ @kbd{make -k} MAKEFLAGS = --unix -k @end example @node The Make Macro SHELL @section The Make Macro @code{SHELL} @cindex @code{SHELL} and @command{make} @cindex @command{make} and @code{SHELL} Posix-compliant @command{make} internally uses the @code{$(SHELL)} macro to spawn shell processes and execute Make rules. This is a builtin macro supplied by @command{make}, but it can be modified by a makefile or by a command-line argument. Not all @command{make} implementations define this @code{SHELL} macro. Tru64 @command{make} is an example; this implementation always uses @code{/bin/sh}. So it's a good idea to always define @code{SHELL} in your makefiles. If you use Autoconf, do @example SHELL = @@SHELL@@ @end example Do not force @code{SHELL = /bin/sh} because that is not correct everywhere. For instance @acronym{DJGPP} lacks @code{/bin/sh}, and when its @acronym{GNU} @code{make} port sees such a setting it enters a special emulation mode where features like pipes and redirections are emulated on top of DOS's @command{command.com}. Unfortunately this emulation is incomplete; for instance it does not handle command substitutions. On @acronym{DJGPP} @code{SHELL} should point to Bash. Posix-compliant @command{make} should never acquire the value of $(SHELL) from the environment, even when @code{make -e} is used (otherwise, think about what would happen to your rules if @code{SHELL=/bin/tcsh}). However not all @command{make} implementations have this exception. For instance it's not surprising that Tru64 @command{make} doesn't protect @code{SHELL}, since it doesn't use it. @example $ @kbd{cat Makefile} SHELL = /bin/sh FOO = foo all: @@echo $(SHELL) @@echo $(FOO) $ @kbd{env SHELL=/bin/tcsh FOO=bar make -e} # Tru64 Make /bin/tcsh bar $ @kbd{env SHELL=/bin/tcsh FOO=bar gmake -e} # GNU make /bin/sh bar @end example @node Comments in Make Rules @section Comments in Make Rules @cindex Comments in @file{Makefile} rules @cindex @file{Makefile} rules and comments Never put comments in a rule. Some @command{make} treat anything starting with a tab as a command for the current rule, even if the tab is immediately followed by a @code{#}. The @command{make} from Tru64 Unix V5.1 is one of them. The following makefile runs @code{# foo} through the shell. @example all: # foo @end example @node obj/ and Make @section The @file{obj/} Subdirectory and Make @cindex @file{obj/}, subdirectory @cindex @acronym{BSD} @command{make} and @file{obj/} Never name one of your subdirectories @file{obj/} if you don't like surprises. If an @file{obj/} directory exists, @acronym{BSD} @command{make} enters it before reading the makefile. Hence the makefile in the current directory is not read. @example $ @kbd{cat Makefile} all: echo Hello $ @kbd{cat obj/Makefile} all: echo World $ @kbd{make} # GNU make echo Hello Hello $ @kbd{pmake} # BSD make echo World World @end example @node make -k Status @section Exit Status of @code{make -k} @cindex @code{make -k} Do not rely on the exit status of @code{make -k}. Some implementations reflect whether they encountered an error in their exit status; other implementations always succeed. @example $ @kbd{cat Makefile} all: false $ @kbd{make -k; echo exit status: $?} # GNU make false make: *** [all] Error 1 exit status: 2 $ @kbd{pmake -k; echo exit status: $?} # BSD make false *** Error code 1 (continuing) exit status: 0 @end example @node VPATH and Make @section @code{VPATH} and Make @cindex @code{VPATH} Posix does not specify the semantics of @code{VPATH}. Typically, @command{make} supports @code{VPATH}, but its implementation is not consistent. Autoconf and Automake support makefiles whose usages of @code{VPATH} are portable to recent-enough popular implementations of @command{make}, but to keep the resulting makefiles portable, a package's makefile prototypes must take the following issues into account. These issues are complicated and are often poorly understood, and installers who use @code{VPATH} should expect to find many bugs in this area. If you use @code{VPATH}, the simplest way to avoid these portability bugs is to stick with @acronym{GNU} @command{make}, since it is the most commonly-used @command{make} among Autoconf users. Here are some known issues with some @code{VPATH} implementations. @menu * VPATH and Double-colon:: Problems with @samp{::} on ancient hosts * $< in Explicit Rules:: @code{$<} does not work in ordinary rules * Automatic Rule Rewriting:: @code{VPATH} goes wild on Solaris * Tru64 Directory Magic:: @command{mkdir} goes wild on Tru64 * Make Target Lookup:: More details about @code{VPATH} lookup @end menu @node VPATH and Double-colon @subsection @code{VPATH} and Double-colon Rules @cindex @code{VPATH} and double-colon rules @cindex double-colon rules and @code{VPATH} With ancient versions of Sun @command{make}, any assignment to @code{VPATH} causes @command{make} to execute only the first set of double-colon rules. However, this problem is no longer of practical concern. @node $< in Explicit Rules @subsection @code{$<} Not Supported in Explicit Rules @cindex explicit rules, @code{$<}, and @code{VPATH} @cindex @code{$<}, explicit rules, and @code{VPATH} @cindex @code{VPATH}, explicit rules, and @code{$<} Using @code{$<} in explicit rules is not portable. The prerequisite file must be named explicitly in the rule. If you want to find the prerequisite via a @code{VPATH} search, you have to code the whole thing manually. @xref{Build Directories}. @node Automatic Rule Rewriting @subsection Automatic Rule Rewriting @cindex @code{VPATH} and automatic rule rewriting @cindex automatic rule rewriting and @code{VPATH} Some @command{make} implementations, such as Solaris and Tru64, search for prerequisites in @code{VPATH} and then rewrite each occurrence as a plain word in the rule. For instance: @example # This isn't portable to GNU make. VPATH = ../pkg/src f.c: if.c cp if.c f.c @end example @noindent executes @code{cp ../pkg/src/if.c f.c} if @file{if.c} is found in @file{../pkg/src}. However, this rule leads to real problems in practice. For example, if the source directory contains an ordinary file named @file{test} that is used in a dependency, Solaris @command{make} rewrites commands like @samp{if test -r foo; @dots{}} to @samp{if ../pkg/src/test -r foo; @dots{}}, which is typically undesirable. To avoid this problem, portable makefiles should never mention a source file whose name is that of a shell keyword like @file{until} or a shell command like @command{cat} or @command{gcc} or @command{test}. Because of these problems @acronym{GNU} @command{make} and many other @command{make} implementations do not rewrite commands, so portable makefiles should search @code{VPATH} manually. It is tempting to write this: @smallexample # This isn't portable to Solaris make. VPATH = ../pkg/src f.c: if.c cp `test -f if.c || echo $(VPATH)/`if.c f.c @end smallexample @noindent However, the ``prerequisite rewriting'' still applies here. So if @file{if.c} is in @file{../pkg/src}, Solaris and Tru64 @command{make} execute @smallexample cp `test -f ../pkg/src/if.c || echo ../pkg/src/`if.c f.c @end smallexample @noindent which reduces to @example cp if.c f.c @end example @noindent and thus fails. Oops. A simple workaround, and good practice anyway, is to use @samp{$?} and @samp{$@@} when possible: @smallexample VPATH = ../pkg/src f.c: if.c cp $? $@@ @end smallexample @noindent but this does not generalize well to commands with multiple prerequisites. A more general workaround is to rewrite the rule so that the prerequisite @file{if.c} never appears as a plain word. For example, these three rules would be safe, assuming @file{if.c} is in @file{../pkg/src} and the other files are in the working directory: @smallexample VPATH = ../pkg/src f.c: if.c f1.c cat `test -f ./if.c || echo $(VPATH)/`if.c f1.c >$@@ g.c: if.c g1.c cat `test -f 'if.c' || echo $(VPATH)/`if.c g1.c >$@@ h.c: if.c h1.c cat `test -f "if.c" || echo $(VPATH)/`if.c h1.c >$@@ @end smallexample Things get worse when your prerequisites are in a macro. @example VPATH = ../pkg/src HEADERS = f.h g.h h.h install-HEADERS: $(HEADERS) for i in $(HEADERS); do \ $(INSTALL) -m 644 \ `test -f $$i || echo $(VPATH)/`$$i \ $(DESTDIR)$(includedir)/$$i; \ done @end example The above @code{install-HEADERS} rule is not Solaris-proof because @code{for i in $(HEADERS);} is expanded to @code{for i in f.h g.h h.h;} where @code{f.h} and @code{g.h} are plain words and are hence subject to @code{VPATH} adjustments. If the three files are in @file{../pkg/src}, the rule is run as: @example for i in ../pkg/src/f.h ../pkg/src/g.h h.h; do \ install -m 644 \ `test -f $i || echo ../pkg/src/`$i \ /usr/local/include/$i; \ done @end example where the two first @command{install} calls fail. For instance, consider the @code{f.h} installation: @example install -m 644 \ `test -f ../pkg/src/f.h || \ echo ../pkg/src/ \ `../pkg/src/f.h \ /usr/local/include/../pkg/src/f.h; @end example @noindent It reduces to: @example install -m 644 \ ../pkg/src/f.h \ /usr/local/include/../pkg/src/f.h; @end example Note that the manual @code{VPATH} search did not cause any problems here; however this command installs @file{f.h} in an incorrect directory. Trying to quote @code{$(HEADERS)} in some way, as we did for @code{foo.c} a few makefiles ago, does not help: @example install-HEADERS: $(HEADERS) headers='$(HEADERS)'; \ for i in $$headers; do \ $(INSTALL) -m 644 \ `test -f $$i || echo $(VPATH)/`$$i \ $(DESTDIR)$(includedir)/$$i; \ done @end example Now, @code{headers='$(HEADERS)'} macroexpands to: @example headers='f.h g.h h.h' @end example @noindent but @code{g.h} is still a plain word. (As an aside, the idiom @code{headers='$(HEADERS)'; for i in $$headers;} is a good idea if @code{$(HEADERS)} can be empty, because some shells diagnose a syntax error on @code{for i in;}.) One workaround is to strip this unwanted @file{../pkg/src/} prefix manually: @example VPATH = ../pkg/src HEADERS = f.h g.h h.h install-HEADERS: $(HEADERS) headers='$(HEADERS)'; \ for i in $$headers; do \ i=`expr "$$i" : '$(VPATH)/\(.*\)'`; $(INSTALL) -m 644 \ `test -f $$i || echo $(VPATH)/`$$i \ $(DESTDIR)$(includedir)/$$i; \ done @end example Automake does something similar. However the above hack works only if the files listed in @code{HEADERS} are in the current directory or a subdirectory; they should not be in an enclosing directory. If we had @code{HEADERS = ../f.h}, the above fragment would fail in a VPATH build with Tru64 @command{make}. The reason is that not only does Tru64 @command{make} rewrite dependencies, but it also simplifies them. Hence @code{../f.h} becomes @code{../pkg/f.h} instead of @code{../pkg/src/../f.h}. This obviously defeats any attempt to strip a leading @file{../pkg/src/} component. The following example makes the behavior of Tru64 @command{make} more apparent. @example $ @kbd{cat Makefile} VPATH = sub all: ../foo echo ../foo $ @kbd{ls} Makefile foo $ @kbd{make} echo foo foo @end example @noindent Dependency @file{../foo} was found in @file{sub/../foo}, but Tru64 @command{make} simplified it as @file{foo}. (Note that the @file{sub/} directory does not even exist, this just means that the simplification occurred before the file was checked for.) For the record here is how SunOS 4 @command{make} behaves on this example. @smallexample $ @kbd{make} make: Fatal error: Don't know how to make target `../foo' $ @kbd{mkdir sub} $ @kbd{make} echo sub/../foo sub/../foo @end smallexample @node Tru64 Directory Magic @subsection Tru64 @command{make} Creates Prerequisite Directories Magically @cindex @code{VPATH} and prerequisite directories @cindex prerequisite directories and @code{VPATH} When a prerequisite is a subdirectory of @code{VPATH}, Tru64 @command{make} creates it in the current directory. @example $ @kbd{mkdir -p foo/bar build} $ @kbd{cd build} $ @kbd{cat >Makefile <dest-stamp @end example @c ======================================== Portable C and C++ Programming @node Portable C and C++ @chapter Portable C and C++ Programming @cindex Portable C and C++ programming C and C++ programs often use low-level features of the underlying system, and therefore are often more difficult to make portable to other platforms. Several standards have been developed to help make your programs more portable. If you write programs with these standards in mind, you can have greater confidence that your programs work on a wide variety of systems. @xref{Standards, , Language Standards Supported by @acronym{GCC}, gcc, Using the @acronym{GNU} Compiler Collection (@acronym{GCC})}, for a list of C-related standards. Many programs also assume the @uref{http://www.opengroup.org/susv3, Posix standard}. Some old code is written to be portable to K&R C, which predates any C standard. K&R C compilers are no longer of practical interest, though, and the rest of section assumes at least C89, the first C standard. Program portability is a huge topic, and this section can only briefly introduce common pitfalls. @xref{System Portability, , Portability between System Types, standards, @acronym{GNU} Coding Standards}, for more information. @menu * Varieties of Unportability:: How to make your programs unportable * Integer Overflow:: When integers get too large * Null Pointers:: Properties of null pointers * Buffer Overruns:: Subscript errors and the like * Volatile Objects:: @code{volatile} and signals * Floating Point Portability:: Portable floating-point arithmetic * Exiting Portably:: Exiting and the exit status @end menu @node Varieties of Unportability @section Varieties of Unportability @cindex portability Autoconf tests and ordinary programs often need to test what is allowed on a system, and therefore they may need to deliberately exceed the boundaries of what the standards allow, if only to see whether an optional feature is present. When you write such a program, you should keep in mind the difference between constraints, unspecified behavior, and undefined behavior. In C, a @dfn{constraint} is a rule that the compiler must enforce. An example constraint is that C programs must not declare a bit-field with negative width. Tests can therefore reliably assume that programs with negative-width bit-fields are rejected by a compiler that conforms to the standard. @dfn{Unspecified behavior} is valid behavior, where the standard allows multiple possibilities. For example, the order of evaluation of function arguments is unspecified. Some unspecified behavior is @dfn{implementation-defined}, i.e., documented by the implementation, but since Autoconf tests cannot read the documentation they cannot distinguish between implementation-defined and other unspecified behavior. It is common for Autoconf tests to probe implementations to determine otherwise-unspecified behavior. @dfn{Undefined behavior} is invalid behavior, where the standard allows the implementation to do anything it pleases. For example, dereferencing a null pointer leads to undefined behavior. If possible, test programs should avoid undefined behavior, since a program with undefined behavior might succeed on a test that should fail. The above rules apply to programs that are intended to conform to the standard. However, strictly-conforming programs are quite rare, since the standards are so limiting. A major goal of Autoconf is to support programs that use implementation features not described by the standard, and it is fairly common for test programs to violate the above rules, if the programs work well enough in practice. @node Integer Overflow @section Integer Overflow @cindex overflow, arithmetic In C, signed integer overflow leads to undefined behavior. However, many programs and Autoconf tests assume that signed integer overflow after addition, subtraction, or multiplication silently wraps around modulo a power of two, using two's complement arithmetic, so long as you cast the resulting value to an integer type or store it into an integer variable. Such programs are portable to the vast majority of modern platforms. However, signed integer division is not always harmless: for example, on CPUs of the i386 family, dividing @code{INT_MIN} by @code{-1} yields a SIGFPE signal which by default terminates the program. Worse, taking the remainder of these two values typically yields the same signal on these CPUs, even though the C standard requires @code{INT_MIN % -1} to yield zero because the expression does not overflow. @acronym{GCC} users might consider using the @option{-ftrapv} option if they are worried about porting their code to the rare platforms where signed integer overflow does not wrap around after addition, subtraction, or multiplication. Unsigned integer overflow reliably wraps around modulo the word size. This is guaranteed by the C standard and is portable in practice. @node Null Pointers @section Properties of Null Pointers @cindex null pointers Most modern hosts reliably fail when you attempt to dereference a null pointer. On almost all modern hosts, null pointers use an all-bits-zero internal representation, so you can reliably use @code{memset} with 0 to set all the pointers in an array to null values. If @code{p} is a null pointer to an object type, the C expression @code{p + 0} always evaluates to @code{p} on modern hosts, even though the standard says that it has undefined behavior. @node Buffer Overruns @section Buffer Overruns and Subscript Errors @cindex buffer overruns Buffer overruns and subscript errors are the most common dangerous errors in C programs. They result in undefined behavior because storing outside an array typically modifies storage that is used by some other object, and most modern systems lack runtime checks to catch these errors. Programs should not rely on buffer overruns being caught. There is one exception to the usual rule that a portable program cannot address outside an array. In C, it is valid to compute the address just past an object, e.g., @code{&a[N]} where @code{a} has @code{N} elements, so long as you do not dereference the resulting pointer. But it is not valid to compute the address just before an object, e.g., @code{&a[-1]}; nor is it valid to compute two past the end, e.g., @code{&a[N+1]}. On most platforms @code{&a[-1] < &a[0] && &a[N] < &a[N+1]}, but this is not reliable in general, and it is usually easy enough to avoid the potential portability problem, e.g., by allocating an extra unused array element at the start or end. @uref{http://valgrind.org/, Valgrind} can catch many overruns. @acronym{GCC} users might also consider using the @option{-fmudflap} option to catch overruns. Buffer overruns are usually caused by off-by-one errors, but there are more subtle ways to get them. Using @code{int} values to index into an array or compute array sizes causes problems on typical 64-bit hosts where an array index might be @math{2^31} or larger. Index values of type @code{size_t} avoid this problem, but cannot be negative. Index values of type @code{ptrdiff_t} are signed, and are wide enough in practice. If you add or multiply two numbers to calculate an array size, e.g., @code{malloc (x * sizeof y + z)}, havoc ensues if the addition or multiplication overflows. Many implementations of the @code{alloca} function silently misbehave and can generate buffer overflows if given sizes that are too large. The size limits are implementation dependent, but are at least 4000 bytes on all platforms that we know about. The standard functions @code{asctime}, @code{asctime_r}, @code{ctime}, @code{ctime_r}, and @code{gets} are prone to buffer overflows, and portable code should not use them unless the inputs are known to be within certain limits. The time-related functions can overflow their buffers if given timestamps out of range (e.g., a year less than -999 or greater than 9999). Time-related buffer overflows cannot happen with recent-enough versions of the @acronym{GNU} C library, but are possible with other implementations. The @code{gets} function is the worst, since it almost invariably overflows its buffer when presented with an input line larger than the buffer. @node Volatile Objects @section Volatile Objects @cindex volatile objects The keyword @code{volatile} is often misunderstood in portable code. Its use inhibits some memory-access optimizations, but programmers often wish that it had a different meaning than it actually does. @code{volatile} was designed for code that accesses special objects like memory-mapped device registers whose contents spontaneously change. Such code is inherently low-level, and it is difficult to specify portably what @code{volatile} means in these cases. The C standard says, ``What constitutes an access to an object that has volatile-qualified type is implementation-defined,'' so in theory each implementation is supposed to fill in the gap by documenting what @code{volatile} means for that implementation. In practice, though, this documentation is usually absent or incomplete. One area of confusion is the distinction between objects defined with volatile types, and volatile lvalues. From the C standard's point of view, an object defined with a volatile type has externally visible behavior. You can think of such objects as having little oscilloscope probes attached to them, so that the user can observe some properties of accesses to them, just as the user can observe data written to output files. However, the standard does not make it clear whether users can observe accesses by volatile lvalues to ordinary objects. For example: @example /* Declare and access a volatile object. Accesses to X are "visible" to users. */ static int volatile x; x = 1; /* Access two ordinary objects via a volatile lvalue. It's not clear whether accesses to *P are "visible". */ int y; int *z = malloc (sizeof (int)); int volatile *p; p = &y; *p = 1; p = z; *p = 1; @end example Programmers often wish that @code{volatile} meant ``Perform the memory access here and now, without merging several memory accesses, without changing the memory word size, and without reordering.'' But the C standard does not require this. For objects defined with a volatile type, accesses must be done before the next sequence point; but otherwise merging, reordering, and word-size change is allowed. Worse, it is not clear from the standard whether volatile lvalues provide more guarantees in general than nonvolatile lvalues, if the underlying objects are ordinary. Even when accessing objects defined with a volatile type, the C standard allows only extremely limited signal handlers: the behavior is undefined if a signal handler reads any nonlocal object, or writes to any nonlocal object whose type is not @code{sig_atomic_t volatile}, or calls any standard library function other than @code{abort}, @code{signal}, and (if C99) @code{_Exit}. Hence C compilers need not worry about a signal handler disturbing ordinary computation, unless the computation accesses a @code{sig_atomic_t volatile} lvalue that is not a local variable. (There is an obscure exception for accesses via a pointer to a volatile character, since it may point into part of a @code{sig_atomic_t volatile} object.) Posix adds to the list of library functions callable from a portable signal handler, but otherwise is like the C standard in this area. Some C implementations allow memory-access optimizations within each translation unit, such that actual behavior agrees with the behavior required by the standard only when calling a function in some other translation unit, and a signal handler acts like it was called from a different translation unit. The C standard hints that in these implementations, objects referred to by signal handlers ``would require explicit specification of @code{volatile} storage, as well as other implementation-defined restrictions.'' But unfortunately even for this special case these other restrictions are often not documented well. @xref{Volatiles, , When is a Volatile Object Accessed?, gcc, Using the @acronym{GNU} Compiler Collection (@acronym{GCC})}, for some restrictions imposed by @acronym{GCC}. @xref{Defining Handlers, , Defining Signal Handlers, libc, The @acronym{GNU} C Library}, for some restrictions imposed by the @acronym{GNU} C library. Restrictions differ on other platforms. If possible, it is best to use a signal handler that fits within the limits imposed by the C and Posix standards. If this is not practical, you can try the following rules of thumb. A signal handler should access only volatile lvalues, preferably lvalues that refer to objects defined with a volatile type, and should not assume that the accessed objects have an internally consistent state if they are larger than a machine word. Furthermore, installers should employ compilers and compiler options that are commonly used for building operating system kernels, because kernels often need more from @code{volatile} than the C Standard requires, and installers who compile an application in a similar environment can sometimes benefit from the extra constraints imposed by kernels on compilers. Admittedly we are handwaving somewhat here, as there are few guarantees in this area; the rules of thumb may help to fix some bugs but there is a good chance that they will not fix them all. For @code{volatile}, C++ has the same problems that C does. Multithreaded applications have even more problems with @code{volatile}, but they are beyond the scope of this section. The bottom line is that using @code{volatile} typically hurts performance but should not hurt correctness. In some cases its use does help correctness, but these cases are often so poorly understood that all too often adding @code{volatile} to a data structure merely alleviates some symptoms of a bug while not fixing the bug in general. @node Floating Point Portability @section Floating Point Portability @cindex floating point Almost all modern systems use IEEE-754 floating point, and it is safe to assume IEEE-754 in most portable code these days. For more information, please see David Goldberg's classic paper @uref{http://www.validlab.com/goldberg/paper.pdf, What Every Computer Scientist Should Know About Floating-Point Arithmetic}. @node Exiting Portably @section Exiting Portably @cindex exiting portably A C or C++ program can exit with status @var{N} by returning @var{N} from the @code{main} function. Portable programs are supposed to exit either with status 0 or @code{EXIT_SUCCESS} to succeed, or with status @code{EXIT_FAILURE} to fail, but in practice it is portable to fail by exiting with status 1, and test programs that assume Posix can fail by exiting with status values from 1 through 255. Programs on SunOS 2.0 (1985) through 3.5.2 (1988) incorrectly exited with zero status when @code{main} returned nonzero, but ancient systems like these are no longer of practical concern. A program can also exit with status @var{N} by passing @var{N} to the @code{exit} function, and a program can fail by calling the @code{abort} function. If a program is specialized to just some platforms, it can fail by calling functions specific to those platforms, e.g., @code{_exit} (Posix) and @code{_Exit} (C99). However, like other functions, an exit function should be declared, typically by including a header. For example, if a C program calls @code{exit}, it should include @file{stdlib.h} either directly or via the default includes (@pxref{Default Includes}). A program can fail due to undefined behavior such as dereferencing a null pointer, but this is not recommended as undefined behavior allows an implementation to do whatever it pleases and this includes exiting successfully. @c ================================================== Manual Configuration @node Manual Configuration @chapter Manual Configuration A few kinds of features can't be guessed automatically by running test programs. For example, the details of the object-file format, or special options that need to be passed to the compiler or linker. You can check for such features using ad-hoc means, such as having @command{configure} check the output of the @code{uname} program, or looking for libraries that are unique to particular systems. However, Autoconf provides a uniform method for handling unguessable features. @menu * Specifying Names:: Specifying the system type * Canonicalizing:: Getting the canonical system type * Using System Type:: What to do with the system type @end menu @node Specifying Names @section Specifying the System Type @cindex System type Like other @acronym{GNU} @command{configure} scripts, Autoconf-generated @command{configure} scripts can make decisions based on a canonical name for the system type, which has the form: @samp{@var{cpu}-@var{vendor}-@var{os}}, where @var{os} can be @samp{@var{system}} or @samp{@var{kernel}-@var{system}} @command{configure} can usually guess the canonical name for the type of system it's running on. To do so it runs a script called @command{config.guess}, which infers the name using the @code{uname} command or symbols predefined by the C preprocessor. Alternately, the user can specify the system type with command line arguments to @command{configure}. Doing so is necessary when cross-compiling. In the most complex case of cross-compiling, three system types are involved. The options to specify them are: @table @option @item --build=@var{build-type} the type of system on which the package is being configured and compiled. It defaults to the result of running @command{config.guess}. @item --host=@var{host-type} the type of system on which the package runs. By default it is the same as the build machine. Specifying it enables the cross-compilation mode. @item --target=@var{target-type} the type of system for which any compiler tools in the package produce code (rarely needed). By default, it is the same as host. @end table If you mean to override the result of @command{config.guess}, use @option{--build}, not @option{--host}, since the latter enables cross-compilation. For historical reasons, passing @option{--host} also changes the build type. Therefore, whenever you specify @option{--host}, be sure to specify @option{--build} too; this will be fixed in the future. So, to enter cross-compilation mode, use a command like this @example ./configure --build=i686-pc-linux-gnu --host=m68k-coff @end example @noindent Note that if you do not specify @option{--host}, @command{configure} fails if it can't run the code generated by the specified compiler. For example, configuring as follows fails: @example ./configure CC=m68k-coff-gcc @end example In the future, when cross-compiling Autoconf will @emph{not} accept tools (compilers, linkers, assemblers) whose name is not prefixed with the host type. The only case when this may be useful is when you really are not cross-compiling, but only building for a least-common-denominator architecture: an example is building for @code{i386-pc-linux-gnu} while running on an @code{i686-pc-linux-gnu} architecture. In this case, some particular pairs might be similar enough to let you get away with the system compilers, but in general the compiler might make bogus assumptions on the host: if you know what you are doing, please create symbolic links from the host compiler to the build compiler. @cindex @command{config.sub} @command{configure} recognizes short aliases for many system types; for example, @samp{decstation} can be used instead of @samp{mips-dec-ultrix4.2}. @command{configure} runs a script called @command{config.sub} to canonicalize system type aliases. This section deliberately omits the description of the obsolete interface; see @ref{Hosts and Cross-Compilation}. @node Canonicalizing @section Getting the Canonical System Type @cindex System type @cindex Canonical system type The following macros make the system type available to @command{configure} scripts. @ovindex build_alias @ovindex host_alias @ovindex target_alias The variables @samp{build_alias}, @samp{host_alias}, and @samp{target_alias} are always exactly the arguments of @option{--build}, @option{--host}, and @option{--target}; in particular, they are left empty if the user did not use them, even if the corresponding @code{AC_CANONICAL} macro was run. Any configure script may use these variables anywhere. These are the variables that should be used when in interaction with the user. If you need to recognize some special environments based on their system type, run the following macros to get canonical system names. These variables are not set before the macro call. If you use these macros, you must distribute @command{config.guess} and @command{config.sub} along with your source code. @xref{Output}, for information about the @code{AC_CONFIG_AUX_DIR} macro which you can use to control in which directory @command{configure} looks for those scripts. @defmac AC_CANONICAL_BUILD @acindex{CANONICAL_BUILD} @ovindex build @ovindex build_cpu @ovindex build_vendor @ovindex build_os Compute the canonical build-system type variable, @code{build}, and its three individual parts @code{build_cpu}, @code{build_vendor}, and @code{build_os}. If @option{--build} was specified, then @code{build} is the canonicalization of @code{build_alias} by @command{config.sub}, otherwise it is determined by the shell script @command{config.guess}. @end defmac @defmac AC_CANONICAL_HOST @acindex{CANONICAL_HOST} @ovindex host @ovindex host_cpu @ovindex host_vendor @ovindex host_os Compute the canonical host-system type variable, @code{host}, and its three individual parts @code{host_cpu}, @code{host_vendor}, and @code{host_os}. If @option{--host} was specified, then @code{host} is the canonicalization of @code{host_alias} by @command{config.sub}, otherwise it defaults to @code{build}. @end defmac @defmac AC_CANONICAL_TARGET @acindex{CANONICAL_TARGET} @ovindex target @ovindex target_cpu @ovindex target_vendor @ovindex target_os Compute the canonical target-system type variable, @code{target}, and its three individual parts @code{target_cpu}, @code{target_vendor}, and @code{target_os}. If @option{--target} was specified, then @code{target} is the canonicalization of @code{target_alias} by @command{config.sub}, otherwise it defaults to @code{host}. @end defmac Note that there can be artifacts due to the backward compatibility code. See @xref{Hosts and Cross-Compilation}, for more. @node Using System Type @section Using the System Type In @file{configure.ac} the system type is generally used by one or more @code{case} statements to select system-specifics. Shell wildcards can be used to match a group of system types. For example, an extra assembler code object file could be chosen, giving access to a CPU cycle counter register. @code{$(CYCLE_OBJ)} in the following would be used in a makefile to add the object to a program or library. @example case $host in alpha*-*-*) CYCLE_OBJ=rpcc.o ;; i?86-*-*) CYCLE_OBJ=rdtsc.o ;; *) CYCLE_OBJ= ;; esac AC_SUBST([CYCLE_OBJ]) @end example @code{AC_CONFIG_LINKS} (@pxref{Configuration Links}) is another good way to select variant source files, for example optimized code for some CPUs. The configured CPU type doesn't always indicate exact CPU types, so some runtime capability checks may be necessary too. @example case $host in alpha*-*-*) AC_CONFIG_LINKS([dither.c:alpha/dither.c]) ;; powerpc*-*-*) AC_CONFIG_LINKS([dither.c:powerpc/dither.c]) ;; *-*-*) AC_CONFIG_LINKS([dither.c:generic/dither.c]) ;; esac @end example The host system type can also be used to find cross-compilation tools with @code{AC_CHECK_TOOL} (@pxref{Generic Programs}). The above examples all show @samp{$host}, since this is where the code is going to run. Only rarely is it necessary to test @samp{$build} (which is where the build is being done). Whenever you're tempted to use @samp{$host} it's worth considering whether some sort of probe would be better. New system types come along periodically or previously missing features are added. Well-written probes can adapt themselves to such things, but hard-coded lists of names can't. Here are some guidelines, @itemize @bullet @item Availability of libraries and library functions should always be checked by probing. @item Variant behavior of system calls is best identified with runtime tests if possible, but bug workarounds or obscure difficulties might have to be driven from @samp{$host}. @item Assembler code is inevitably highly CPU-specific and is best selected according to @samp{$host_cpu}. @item Assembler variations like underscore prefix on globals or ELF versus COFF type directives are however best determined by probing, perhaps even examining the compiler output. @end itemize @samp{$target} is for use by a package creating a compiler or similar. For ordinary packages it's meaningless and should not be used. It indicates what the created compiler should generate code for, if it can cross-compile. @samp{$target} generally selects various hard-coded CPU and system conventions, since usually the compiler or tools under construction themselves determine how the target works. @c ===================================================== Site Configuration. @node Site Configuration @chapter Site Configuration @command{configure} scripts support several kinds of local configuration decisions. There are ways for users to specify where external software packages are, include or exclude optional features, install programs under modified names, and set default values for @command{configure} options. @menu * Help Formatting:: Customizing @samp{configure --help} * External Software:: Working with other optional software * Package Options:: Selecting optional features * Pretty Help Strings:: Formatting help string * Site Details:: Configuring site details * Transforming Names:: Changing program names when installing * Site Defaults:: Giving @command{configure} local defaults @end menu @node Help Formatting @section Controlling Help Output Users consult @samp{configure --help} to learn of configuration decisions specific to your package. By default, @command{configure} breaks this output into sections for each type of option; within each section, help strings appear in the order @file{configure.ac} defines them: @example Optional Features: @dots{} --enable-bar include bar Optional Packages: @dots{} --with-foo use foo @end example @defmac AC_PRESERVE_HELP_ORDER @acindex{PRESERVE_HELP_ORDER} Request an alternate @option{--help} format, in which options of all types appear together, in the order defined. Call this macro before any @code{AC_ARG_ENABLE} or @code{AC_ARG_WITH}. @example Optional Features and Packages: @dots{} --enable-bar include bar --with-foo use foo @end example @end defmac @node External Software @section Working With External Software @cindex External software Some packages require, or can optionally use, other software packages that are already installed. The user can give @command{configure} command line options to specify which such external software to use. The options have one of these forms: @c FIXME: Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something @c awful. @example --with-@var{package}[=@var{arg}] --without-@var{package} @end example For example, @option{--with-gnu-ld} means work with the @acronym{GNU} linker instead of some other linker. @option{--with-x} means work with The X Window System. The user can give an argument by following the package name with @samp{=} and the argument. Giving an argument of @samp{no} is for packages that are used by default; it says to @emph{not} use the package. An argument that is neither @samp{yes} nor @samp{no} could include a name or number of a version of the other package, to specify more precisely which other package this program is supposed to work with. If no argument is given, it defaults to @samp{yes}. @option{--without-@var{package}} is equivalent to @option{--with-@var{package}=no}. @command{configure} scripts do not complain about @option{--with-@var{package}} options that they do not support. This behavior permits configuring a source tree containing multiple packages with a top-level @command{configure} script when the packages support different options, without spurious error messages about options that some of the packages support. An unfortunate side effect is that option spelling errors are not diagnosed. No better approach to this problem has been suggested so far. For each external software package that may be used, @file{configure.ac} should call @code{AC_ARG_WITH} to detect whether the @command{configure} user asked to use it. Whether each package is used or not by default, and which arguments are valid, is up to you. @defmac AC_ARG_WITH (@var{package}, @var{help-string}, @ovar{action-if-given}, @ovar{action-if-not-given}) @acindex{ARG_WITH} If the user gave @command{configure} the option @option{--with-@var{package}} or @option{--without-@var{package}}, run shell commands @var{action-if-given}. If neither option was given, run shell commands @var{action-if-not-given}. The name @var{package} indicates another software package that this program should work with. It should consist only of alphanumeric characters, dashes, and dots. The option's argument is available to the shell commands @var{action-if-given} in the shell variable @code{withval}, which is actually just the value of the shell variable @code{with_@var{package}}, with any non-alphanumeric characters changed into @samp{_}. You may use that variable instead, if you wish. The argument @var{help-string} is a description of the option that looks like this: @example --with-readline support fancy command line editing @end example @noindent @var{help-string} may be more than one line long, if more detail is needed. Just make sure the columns line up in @samp{configure --help}. Avoid tabs in the help string. You'll need to enclose the help string in @samp{[} and @samp{]} in order to produce the leading blanks. You should format your @var{help-string} with the macro @code{AS_HELP_STRING} (@pxref{Pretty Help Strings}). The following example shows how to use the @code{AC_ARG_WITH} macro in a common situation. You want to let the user decide whether to enable support for an external library (e.g., the readline library); if the user specified neither @option{--with-readline} nor @option{--without-readline}, you want to enable support for readline only if the library is available on the system. @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is solved. @example AC_ARG_WITH([readline], [AS_HELP_STRING([--with-readline], [support fancy command line editing @@<:@@default=check@@:>@@])], [], [with_readline=check]) LIBREADLINE= AS_IF([test "x$with_readline" != xno], [AC_CHECK_LIB([readline], [main], [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) AC_DEFINE([HAVE_LIBREADLINE], [1], [Define if you have libreadline]) ], [if test "x$with_readline" != xcheck; then AC_MSG_FAILURE( [--with-readline was given, but test for readline failed]) fi ], -lncurses)]) @end example The next example shows how to use @code{AC_ARG_WITH} to give the user the possibility to enable support for the readline library, in case it is still experimental and not well tested, and is therefore disabled by default. @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is solved. @example AC_ARG_WITH([readline], [AS_HELP_STRING([--with-readline], [enable experimental support for readline])], [], [with_readline=no]) LIBREADLINE= AS_IF([test "x$with_readline" != xno], [AC_CHECK_LIB([readline], [main], [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) AC_DEFINE([HAVE_LIBREADLINE], [1], [Define if you have libreadline]) ], [AC_MSG_FAILURE( [--with-readline was given, but test for readline failed])], [-lncurses])]) @end example The last example shows how to use @code{AC_ARG_WITH} to give the user the possibility to disable support for the readline library, given that it is an important feature and that it should be enabled by default. @c FIXME: Remove AS_IF when the problem of AC_REQUIRE within `if' is solved. @example AC_ARG_WITH([readline], [AS_HELP_STRING([--without-readline], [disable support for readline])], [], [with_readline=yes]) LIBREADLINE= AS_IF([test "x$with_readline" != xno], [AC_CHECK_LIB([readline], [main], [AC_SUBST([LIBREADLINE], ["-lreadline -lncurses"]) AC_DEFINE([HAVE_LIBREADLINE], [1], [Define if you have libreadline]) ], [AC_MSG_FAILURE( [readline test failed (--without-readline to disable)])], [-lncurses])]) @end example These three examples can be easily adapted to the case where @code{AC_ARG_ENABLE} should be preferred to @code{AC_ARG_WITH} (see @ref{Package Options}). @end defmac @defmac AC_WITH (@var{package}, @var{action-if-given}, @ovar{action-if-not-given}) @acindex{WITH} This is an obsolete version of @code{AC_ARG_WITH} that does not support providing a help string. @end defmac @node Package Options @section Choosing Package Options @cindex Package options @cindex Options, package If a software package has optional compile-time features, the user can give @command{configure} command line options to specify whether to compile them. The options have one of these forms: @c FIXME: Can't use @ovar here, Texinfo 4.0 goes lunatic and emits something @c awful. @example --enable-@var{feature}[=@var{arg}] --disable-@var{feature} @end example These options allow users to choose which optional features to build and install. @option{--enable-@var{feature}} options should never make a feature behave differently or cause one feature to replace another. They should only cause parts of the program to be built rather than left out. The user can give an argument by following the feature name with @samp{=} and the argument. Giving an argument of @samp{no} requests that the feature @emph{not} be made available. A feature with an argument looks like @option{--enable-debug=stabs}. If no argument is given, it defaults to @samp{yes}. @option{--disable-@var{feature}} is equivalent to @option{--enable-@var{feature}=no}. @command{configure} scripts do not complain about @option{--enable-@var{feature}} options that they do not support. This behavior permits configuring a source tree containing multiple packages with a top-level @command{configure} script when the packages support different options, without spurious error messages about options that some of the packages support. An unfortunate side effect is that option spelling errors are not diagnosed. No better approach to this problem has been suggested so far. For each optional feature, @file{configure.ac} should call @code{AC_ARG_ENABLE} to detect whether the @command{configure} user asked to include it. Whether each feature is included or not by default, and which arguments are valid, is up to you. @defmac AC_ARG_ENABLE (@var{feature}, @var{help-string}, @ovar{action-if-given}, @ovar{action-if-not-given}) @acindex{ARG_ENABLE} If the user gave @command{configure} the option @option{--enable-@var{feature}} or @option{--disable-@var{feature}}, run shell commands @var{action-if-given}. If neither option was given, run shell commands @var{action-if-not-given}. The name @var{feature} indicates an optional user-level facility. It should consist only of alphanumeric characters, dashes, and dots. The option's argument is available to the shell commands @var{action-if-given} in the shell variable @code{enableval}, which is actually just the value of the shell variable @code{enable_@var{feature}}, with any non-alphanumeric characters changed into @samp{_}. You may use that variable instead, if you wish. The @var{help-string} argument is like that of @code{AC_ARG_WITH} (@pxref{External Software}). You should format your @var{help-string} with the macro @code{AS_HELP_STRING} (@pxref{Pretty Help Strings}). See the examples suggested with the definition of @code{AC_ARG_WITH} (@pxref{External Software}) to get an idea of possible applications of @code{AC_ARG_ENABLE}. @end defmac @defmac AC_ENABLE (@var{feature}, @var{action-if-given}, @ovar{action-if-not-given}) @acindex{ENABLE} This is an obsolete version of @code{AC_ARG_ENABLE} that does not support providing a help string. @end defmac @node Pretty Help Strings @section Making Your Help Strings Look Pretty @cindex Help strings Properly formatting the @samp{help strings} which are used in @code{AC_ARG_WITH} (@pxref{External Software}) and @code{AC_ARG_ENABLE} (@pxref{Package Options}) can be challenging. Specifically, you want your own @samp{help strings} to line up in the appropriate columns of @samp{configure --help} just like the standard Autoconf @samp{help strings} do. This is the purpose of the @code{AS_HELP_STRING} macro. @defmac AS_HELP_STRING (@var{left-hand-side}, @var{right-hand-side}) @acindex{HELP_STRING} Expands into an help string that looks pretty when the user executes @samp{configure --help}. It is typically used in @code{AC_ARG_WITH} (@pxref{External Software}) or @code{AC_ARG_ENABLE} (@pxref{Package Options}). The following example makes this clearer. @example AC_ARG_WITH([foo], [AS_HELP_STRING([--with-foo], [use foo (default is no)])], [use_foo=$withval], [use_foo=no]) @end example The second argument of @code{AS_HELP_STRING} is not a literal, and should not be double quoted. @xref{Autoconf Language}, for a more detailed explanation. Then the last few lines of @samp{configure --help} appear like this: @example --enable and --with options recognized: --with-foo use foo (default is no) @end example The @code{AS_HELP_STRING} macro is particularly helpful when the @var{left-hand-side} and/or @var{right-hand-side} are composed of macro arguments, as shown in the following example. @example AC_DEFUN([MY_ARG_WITH], [AC_ARG_WITH([$1], [AS_HELP_STRING([--with-$1], [use $1 (default is $2)])], [use_[]$1=$withval], [use_[]$1=$2])]) @end example @end defmac @node Site Details @section Configuring Site Details @cindex Site details Some software packages require complex site-specific information. Some examples are host names to use for certain services, company names, and email addresses to contact. Since some configuration scripts generated by Metaconfig ask for such information interactively, people sometimes wonder how to get that information in Autoconf-generated configuration scripts, which aren't interactive. Such site configuration information should be put in a file that is edited @emph{only by users}, not by programs. The location of the file can either be based on the @code{prefix} variable, or be a standard location such as the user's home directory. It could even be specified by an environment variable. The programs should examine that file at runtime, rather than at compile time. Runtime configuration is more convenient for users and makes the configuration process simpler than getting the information while configuring. @xref{Directory Variables, , Variables for Installation Directories, standards, @acronym{GNU} Coding Standards}, for more information on where to put data files. @node Transforming Names @section Transforming Program Names When Installing @cindex Transforming program names @cindex Program names, transforming Autoconf supports changing the names of programs when installing them. In order to use these transformations, @file{configure.ac} must call the macro @code{AC_ARG_PROGRAM}. @defmac AC_ARG_PROGRAM @acindex{ARG_PROGRAM} @ovindex program_transform_name Place in output variable @code{program_transform_name} a sequence of @code{sed} commands for changing the names of installed programs. If any of the options described below are given to @command{configure}, program names are transformed accordingly. Otherwise, if @code{AC_CANONICAL_TARGET} has been called and a @option{--target} value is given, the target type followed by a dash is used as a prefix. Otherwise, no program name transformation is done. @end defmac @menu * Transformation Options:: @command{configure} options to transform names * Transformation Examples:: Sample uses of transforming names * Transformation Rules:: Makefile uses of transforming names @end menu @node Transformation Options @subsection Transformation Options You can specify name transformations by giving @command{configure} these command line options: @table @option @item --program-prefix=@var{prefix} prepend @var{prefix} to the names; @item --program-suffix=@var{suffix} append @var{suffix} to the names; @item --program-transform-name=@var{expression} perform @code{sed} substitution @var{expression} on the names. @end table @node Transformation Examples @subsection Transformation Examples These transformations are useful with programs that can be part of a cross-compilation development environment. For example, a cross-assembler running on a Sun 4 configured with @option{--target=i960-vxworks} is normally installed as @file{i960-vxworks-as}, rather than @file{as}, which could be confused with a native Sun 4 assembler. You can force a program name to begin with @file{g}, if you don't want @acronym{GNU} programs installed on your system to shadow other programs with the same name. For example, if you configure @acronym{GNU} @code{diff} with @option{--program-prefix=g}, then when you run @samp{make install} it is installed as @file{/usr/local/bin/gdiff}. As a more sophisticated example, you could use @example --program-transform-name='s/^/g/; s/^gg/g/; s/^gless/less/' @end example @noindent to prepend @samp{g} to most of the program names in a source tree, excepting those like @code{gdb} that already have one and those like @code{less} and @code{lesskey} that aren't @acronym{GNU} programs. (That is assuming that you have a source tree containing those programs that is set up to use this feature.) One way to install multiple versions of some programs simultaneously is to append a version number to the name of one or both. For example, if you want to keep Autoconf version 1 around for awhile, you can configure Autoconf version 2 using @option{--program-suffix=2} to install the programs as @file{/usr/local/bin/autoconf2}, @file{/usr/local/bin/autoheader2}, etc. Nevertheless, pay attention that only the binaries are renamed, therefore you'd have problems with the library files which might overlap. @node Transformation Rules @subsection Transformation Rules Here is how to use the variable @code{program_transform_name} in a @file{Makefile.in}: @example PROGRAMS = cp ls rm transform = @@program_transform_name@@ install: for p in $(PROGRAMS); do \ $(INSTALL_PROGRAM) $$p $(DESTDIR)$(bindir)/`echo $$p | \ sed '$(transform)'`; \ done uninstall: for p in $(PROGRAMS); do \ rm -f $(DESTDIR)$(bindir)/`echo $$p | sed '$(transform)'`; \ done @end example It is guaranteed that @code{program_transform_name} is never empty, and that there are no useless separators. Therefore you may safely embed @code{program_transform_name} within a sed program using @samp{;}: @example transform = @@program_transform_name@@ transform_exe = s/$(EXEEXT)$$//;$(transform);s/$$/$(EXEEXT)/ @end example Whether to do the transformations on documentation files (Texinfo or @code{man}) is a tricky question; there seems to be no perfect answer, due to the several reasons for name transforming. Documentation is not usually particular to a specific architecture, and Texinfo files do not conflict with system documentation. But they might conflict with earlier versions of the same files, and @code{man} pages sometimes do conflict with system documentation. As a compromise, it is probably best to do name transformations on @code{man} pages but not on Texinfo manuals. @node Site Defaults @section Setting Site Defaults @cindex Site defaults Autoconf-generated @command{configure} scripts allow your site to provide default values for some configuration values. You do this by creating site- and system-wide initialization files. @evindex CONFIG_SITE If the environment variable @code{CONFIG_SITE} is set, @command{configure} uses its value as the name of a shell script to read. Otherwise, it reads the shell script @file{@var{prefix}/share/config.site} if it exists, then @file{@var{prefix}/etc/config.site} if it exists. Thus, settings in machine-specific files override those in machine-independent ones in case of conflict. Site files can be arbitrary shell scripts, but only certain kinds of code are really appropriate to be in them. Because @command{configure} reads any cache file after it has read any site files, a site file can define a default cache file to be shared between all Autoconf-generated @command{configure} scripts run on that system (@pxref{Cache Files}). If you set a default cache file in a site file, it is a good idea to also set the output variable @code{CC} in that site file, because the cache file is only valid for a particular compiler, but many systems have several available. You can examine or override the value set by a command line option to @command{configure} in a site file; options set shell variables that have the same names as the options, with any dashes turned into underscores. The exceptions are that @option{--without-} and @option{--disable-} options are like giving the corresponding @option{--with-} or @option{--enable-} option and the value @samp{no}. Thus, @option{--cache-file=localcache} sets the variable @code{cache_file} to the value @samp{localcache}; @option{--enable-warnings=no} or @option{--disable-warnings} sets the variable @code{enable_warnings} to the value @samp{no}; @option{--prefix=/usr} sets the variable @code{prefix} to the value @samp{/usr}; etc. Site files are also good places to set default values for other output variables, such as @code{CFLAGS}, if you need to give them non-default values: anything you would normally do, repetitively, on the command line. If you use non-default values for @var{prefix} or @var{exec_prefix} (wherever you locate the site file), you can set them in the site file if you specify it with the @code{CONFIG_SITE} environment variable. You can set some cache values in the site file itself. Doing this is useful if you are cross-compiling, where it is impossible to check features that require running a test program. You could ``prime the cache'' by setting those values correctly for that system in @file{@var{prefix}/etc/config.site}. To find out the names of the cache variables you need to set, look for shell variables with @samp{_cv_} in their names in the affected @command{configure} scripts, or in the Autoconf M4 source code for those macros. The cache file is careful to not override any variables set in the site files. Similarly, you should not override command-line options in the site files. Your code should check that variables such as @code{prefix} and @code{cache_file} have their default values (as set near the top of @command{configure}) before changing them. Here is a sample file @file{/usr/share/local/gnu/share/config.site}. The command @samp{configure --prefix=/usr/share/local/gnu} would read this file (if @code{CONFIG_SITE} is not set to a different file). @example # config.site for configure # # Change some defaults. test "$prefix" = NONE && prefix=/usr/share/local/gnu test "$exec_prefix" = NONE && exec_prefix=/usr/local/gnu test "$sharedstatedir" = '$prefix/com' && sharedstatedir=/var test "$localstatedir" = '$prefix/var' && localstatedir=/var # Give Autoconf 2.x generated configure scripts a shared default # cache file for feature test results, architecture-specific. if test "$cache_file" = /dev/null; then cache_file="$prefix/var/config.cache" # A cache file is only valid for one C compiler. CC=gcc fi @end example @c ============================================== Running configure Scripts. @node Running configure Scripts @chapter Running @command{configure} Scripts @cindex @command{configure} Below are instructions on how to configure a package that uses a @command{configure} script, suitable for inclusion as an @file{INSTALL} file in the package. A plain-text version of @file{INSTALL} which you may use comes with Autoconf. @menu * Basic Installation:: Instructions for typical cases * Compilers and Options:: Selecting compilers and optimization * Multiple Architectures:: Compiling for multiple architectures at once * Installation Names:: Installing in different directories * Optional Features:: Selecting optional features * System Type:: Specifying the system type * Sharing Defaults:: Setting site-wide defaults for @command{configure} * Defining Variables:: Specifying the compiler etc. * configure Invocation:: Changing how @command{configure} runs @end menu @set autoconf @include install.texi @c ============================================== Recreating a Configuration @node config.status Invocation @chapter Recreating a Configuration @cindex @command{config.status} The @command{configure} script creates a file named @file{config.status}, which actually configures, @dfn{instantiates}, the template files. It also records the configuration options that were specified when the package was last configured in case reconfiguring is needed. Synopsis: @example ./config.status @var{option}@dots{} [@var{file}@dots{}] @end example It configures the @var{files}; if none are specified, all the templates are instantiated. The files must be specified without their dependencies, as in @example ./config.status foobar @end example @noindent not @example ./config.status foobar:foo.in:bar.in @end example The supported options are: @table @option @item --help @itemx -h Print a summary of the command line options, the list of the template files, and exit. @item --version @itemx -V Print the version number of Autoconf and the configuration settings, and exit. @item --silent @itemx --quiet @itemx -q Do not print progress messages. @item --debug @itemx -d Don't remove the temporary files. @item --file=@var{file}[:@var{template}] Require that @var{file} be instantiated as if @samp{AC_CONFIG_FILES(@var{file}:@var{template})} was used. Both @var{file} and @var{template} may be @samp{-} in which case the standard output and/or standard input, respectively, is used. If a @var{template} file name is relative, it is first looked for in the build tree, and then in the source tree. @xref{Configuration Actions}, for more details. This option and the following ones provide one way for separately distributed packages to share the values computed by @command{configure}. Doing so can be useful if some of the packages need a superset of the features that one of them, perhaps a common library, does. These options allow a @file{config.status} file to create files other than the ones that its @file{configure.ac} specifies, so it can be used for a different package. @item --header=@var{file}[:@var{template}] Same as @option{--file} above, but with @samp{AC_CONFIG_HEADERS}. @item --recheck Ask @file{config.status} to update itself and exit (no instantiation). This option is useful if you change @command{configure}, so that the results of some tests might be different from the previous run. The @option{--recheck} option reruns @command{configure} with the same arguments you used before, plus the @option{--no-create} option, which prevents @command{configure} from running @file{config.status} and creating @file{Makefile} and other files, and the @option{--no-recursion} option, which prevents @command{configure} from running other @command{configure} scripts in subdirectories. (This is so other Make rules can run @file{config.status} when it changes; @pxref{Automatic Remaking}, for an example). @end table @file{config.status} checks several optional environment variables that can alter its behavior: @defvar CONFIG_SHELL @evindex CONFIG_SHELL The shell with which to run @command{configure} for the @option{--recheck} option. It must be Bourne-compatible. The default is a shell that supports @code{LINENO} if available, and @file{/bin/sh} otherwise. Invoking @command{configure} by hand bypasses this setting, so you may need to use a command like @samp{CONFIG_SHELL=/bin/bash /bin/bash ./configure} to insure that the same shell is used everywhere. The absolute name of the shell should be passed. @end defvar @defvar CONFIG_STATUS @evindex CONFIG_STATUS The file name to use for the shell script that records the configuration. The default is @file{./config.status}. This variable is useful when one package uses parts of another and the @command{configure} scripts shouldn't be merged because they are maintained separately. @end defvar You can use @file{./config.status} in your makefiles. For example, in the dependencies given above (@pxref{Automatic Remaking}), @file{config.status} is run twice when @file{configure.ac} has changed. If that bothers you, you can make each run only regenerate the files for that rule: @example @group config.h: stamp-h stamp-h: config.h.in config.status ./config.status config.h echo > stamp-h Makefile: Makefile.in config.status ./config.status Makefile @end group @end example The calling convention of @file{config.status} has changed; see @ref{Obsolete config.status Use}, for details. @c =================================================== Obsolete Constructs @node Obsolete Constructs @chapter Obsolete Constructs @cindex Obsolete constructs Autoconf changes, and throughout the years some constructs have been obsoleted. Most of the changes involve the macros, but in some cases the tools themselves, or even some concepts, are now considered obsolete. You may completely skip this chapter if you are new to Autoconf. Its intention is mainly to help maintainers updating their packages by understanding how to move to more modern constructs. @menu * Obsolete config.status Use:: Different calling convention * acconfig.h:: Additional entries in @file{config.h.in} * autoupdate Invocation:: Automatic update of @file{configure.ac} * Obsolete Macros:: Backward compatibility macros * Autoconf 1:: Tips for upgrading your files * Autoconf 2.13:: Some fresher tips @end menu @node Obsolete config.status Use @section Obsolete @file{config.status} Invocation @file{config.status} now supports arguments to specify the files to instantiate; see @ref{config.status Invocation}, for more details. Before, environment variables had to be used. @defvar CONFIG_COMMANDS @evindex CONFIG_COMMANDS The tags of the commands to execute. The default is the arguments given to @code{AC_OUTPUT} and @code{AC_CONFIG_COMMANDS} in @file{configure.ac}. @end defvar @defvar CONFIG_FILES @evindex CONFIG_FILES The files in which to perform @samp{@@@var{variable}@@} substitutions. The default is the arguments given to @code{AC_OUTPUT} and @code{AC_CONFIG_FILES} in @file{configure.ac}. @end defvar @defvar CONFIG_HEADERS @evindex CONFIG_HEADERS The files in which to substitute C @code{#define} statements. The default is the arguments given to @code{AC_CONFIG_HEADERS}; if that macro was not called, @file{config.status} ignores this variable. @end defvar @defvar CONFIG_LINKS @evindex CONFIG_LINKS The symbolic links to establish. The default is the arguments given to @code{AC_CONFIG_LINKS}; if that macro was not called, @file{config.status} ignores this variable. @end defvar In @ref{config.status Invocation}, using this old interface, the example would be: @example @group config.h: stamp-h stamp-h: config.h.in config.status CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_FILES= \ CONFIG_HEADERS=config.h ./config.status echo > stamp-h Makefile: Makefile.in config.status CONFIG_COMMANDS= CONFIG_LINKS= CONFIG_HEADERS= \ CONFIG_FILES=Makefile ./config.status @end group @end example @noindent (If @file{configure.ac} does not call @code{AC_CONFIG_HEADERS}, there is no need to set @code{CONFIG_HEADERS} in the @code{make} rules. Equally for @code{CONFIG_COMMANDS}, etc.) @node acconfig.h @section @file{acconfig.h} @cindex @file{acconfig.h} @cindex @file{config.h.top} @cindex @file{config.h.bot} In order to produce @file{config.h.in}, @command{autoheader} needs to build or to find templates for each symbol. Modern releases of Autoconf use @code{AH_VERBATIM} and @code{AH_TEMPLATE} (@pxref{Autoheader Macros}), but in older releases a file, @file{acconfig.h}, contained the list of needed templates. @command{autoheader} copied comments and @code{#define} and @code{#undef} statements from @file{acconfig.h} in the current directory, if present. This file used to be mandatory if you @code{AC_DEFINE} any additional symbols. Modern releases of Autoconf also provide @code{AH_TOP} and @code{AH_BOTTOM} if you need to prepend/append some information to @file{config.h.in}. Ancient versions of Autoconf had a similar feature: if @file{./acconfig.h} contains the string @samp{@@TOP@@}, @command{autoheader} copies the lines before the line containing @samp{@@TOP@@} into the top of the file that it generates. Similarly, if @file{./acconfig.h} contains the string @samp{@@BOTTOM@@}, @command{autoheader} copies the lines after that line to the end of the file it generates. Either or both of those strings may be omitted. An even older alternate way to produce the same effect in ancient versions of Autoconf is to create the files @file{@var{file}.top} (typically @file{config.h.top}) and/or @file{@var{file}.bot} in the current directory. If they exist, @command{autoheader} copies them to the beginning and end, respectively, of its output. In former versions of Autoconf, the files used in preparing a software package for distribution were: @example @group configure.ac --. .------> autoconf* -----> configure +---+ [aclocal.m4] --+ `---. [acsite.m4] ---' | +--> [autoheader*] -> [config.h.in] [acconfig.h] ----. | +-----' [config.h.top] --+ [config.h.bot] --' @end group @end example Using only the @code{AH_} macros, @file{configure.ac} should be self-contained, and should not depend upon @file{acconfig.h} etc. @node autoupdate Invocation @section Using @command{autoupdate} to Modernize @file{configure.ac} @cindex @command{autoupdate} The @command{autoupdate} program updates a @file{configure.ac} file that calls Autoconf macros by their old names to use the current macro names. In version 2 of Autoconf, most of the macros were renamed to use a more uniform and descriptive naming scheme. @xref{Macro Names}, for a description of the new scheme. Although the old names still work (@pxref{Obsolete Macros}, for a list of the old macros and the corresponding new names), you can make your @file{configure.ac} files more readable and make it easier to use the current Autoconf documentation if you update them to use the new macro names. @evindex SIMPLE_BACKUP_SUFFIX If given no arguments, @command{autoupdate} updates @file{configure.ac}, backing up the original version with the suffix @file{~} (or the value of the environment variable @code{SIMPLE_BACKUP_SUFFIX}, if that is set). If you give @command{autoupdate} an argument, it reads that file instead of @file{configure.ac} and writes the updated file to the standard output. @noindent @command{autoupdate} accepts the following options: @table @option @item --help @itemx -h Print a summary of the command line options and exit. @item --version @itemx -V Print the version number of Autoconf and exit. @item --verbose @itemx -v Report processing steps. @item --debug @itemx -d Don't remove the temporary files. @item --force @itemx -f Force the update even if the file has not changed. Disregard the cache. @item --include=@var{dir} @itemx -I @var{dir} Also look for input files in @var{dir}. Multiple invocations accumulate. Directories are browsed from last to first. @end table @node Obsolete Macros @section Obsolete Macros Several macros are obsoleted in Autoconf, for various reasons (typically they failed to quote properly, couldn't be extended for more recent issues, etc.). They are still supported, but deprecated: their use should be avoided. During the jump from Autoconf version 1 to version 2, most of the macros were renamed to use a more uniform and descriptive naming scheme, but their signature did not change. @xref{Macro Names}, for a description of the new naming scheme. Below, if there is just the mapping from old names to new names for these macros, the reader is invited to refer to the definition of the new macro for the signature and the description. @defmac AC_ALLOCA @acindex{ALLOCA} @code{AC_FUNC_ALLOCA} @end defmac @defmac AC_ARG_ARRAY @acindex{ARG_ARRAY} removed because of limited usefulness @end defmac @defmac AC_C_CROSS @acindex{C_CROSS} This macro is obsolete; it does nothing. @end defmac @defmac AC_C_LONG_DOUBLE @acindex{C_LONG_DOUBLE} @cvindex HAVE_LONG_DOUBLE If the C compiler supports a working @code{long double} type with more range or precision than the @code{double} type, define @code{HAVE_LONG_DOUBLE}. You should use @code{AC_TYPE_LONG_DOUBLE} or @code{AC_TYPE_LONG_DOUBLE_WIDER} instead. @xref{Particular Types}. @end defmac @defmac AC_CANONICAL_SYSTEM @acindex{CANONICAL_SYSTEM} Determine the system type and set output variables to the names of the canonical system types. @xref{Canonicalizing}, for details about the variables this macro sets. The user is encouraged to use either @code{AC_CANONICAL_BUILD}, or @code{AC_CANONICAL_HOST}, or @code{AC_CANONICAL_TARGET}, depending on the needs. Using @code{AC_CANONICAL_TARGET} is enough to run the two other macros. @end defmac @defmac AC_CHAR_UNSIGNED @acindex{CHAR_UNSIGNED} @code{AC_C_CHAR_UNSIGNED} @end defmac @defmac AC_CHECK_TYPE (@var{type}, @var{default}) @acindex{CHECK_TYPE} Autoconf, up to 2.13, used to provide this version of @code{AC_CHECK_TYPE}, deprecated because of its flaws. First, although it is a member of the @code{CHECK} clan, it does more than just checking. Secondly, missing types are defined using @code{#define}, not @code{typedef}, and this can lead to problems in the case of pointer types. This use of @code{AC_CHECK_TYPE} is obsolete and discouraged; see @ref{Generic Types}, for the description of the current macro. If the type @var{type} is not defined, define it to be the C (or C++) builtin type @var{default}, e.g., @samp{short int} or @samp{unsigned int}. This macro is equivalent to: @example AC_CHECK_TYPE([@var{type}], [], [AC_DEFINE_UNQUOTED([@var{type}], [@var{default}], [Define to `@var{default}' if does not define.])]) @end example In order to keep backward compatibility, the two versions of @code{AC_CHECK_TYPE} are implemented, selected by a simple heuristics: @enumerate @item If there are three or four arguments, the modern version is used. @item If the second argument appears to be a C or C++ type, then the obsolete version is used. This happens if the argument is a C or C++ @emph{builtin} type or a C identifier ending in @samp{_t}, optionally followed by one of @samp{[(* } and then by a string of zero or more characters taken from the set @samp{[]()* _a-zA-Z0-9}. @item If the second argument is spelled with the alphabet of valid C and C++ types, the user is warned and the modern version is used. @item Otherwise, the modern version is used. @end enumerate @noindent You are encouraged either to use a valid builtin type, or to use the equivalent modern code (see above), or better yet, to use @code{AC_CHECK_TYPES} together with @example #ifndef HAVE_LOFF_T typedef loff_t off_t; #endif @end example @end defmac @c end of AC_CHECK_TYPE @defmac AC_CHECKING (@var{feature-description}) @acindex{CHECKING} Same as @samp{AC_MSG_NOTICE([checking @var{feature-description}@dots{}]}. @end defmac @defmac AC_COMPILE_CHECK (@var{echo-text}, @var{includes}, @var{function-body}, @var{action-if-true}, @ovar{action-if-false}) @acindex{COMPILE_CHECK} This is an obsolete version of @code{AC_TRY_COMPILE} itself replaced by @code{AC_COMPILE_IFELSE} (@pxref{Running the Compiler}), with the addition that it prints @samp{checking for @var{echo-text}} to the standard output first, if @var{echo-text} is non-empty. Use @code{AC_MSG_CHECKING} and @code{AC_MSG_RESULT} instead to print messages (@pxref{Printing Messages}). @end defmac @defmac AC_CONST @acindex{CONST} @code{AC_C_CONST} @end defmac @defmac AC_CROSS_CHECK @acindex{CROSS_CHECK} Same as @code{AC_C_CROSS}, which is obsolete too, and does nothing @code{:-)}. @end defmac @defmac AC_CYGWIN @acindex{CYGWIN} Check for the Cygwin environment in which case the shell variable @code{CYGWIN} is set to @samp{yes}. Don't use this macro, the dignified means to check the nature of the host is using @code{AC_CANONICAL_HOST}. As a matter of fact this macro is defined as: @example AC_REQUIRE([AC_CANONICAL_HOST])[]dnl case $host_os in *cygwin* ) CYGWIN=yes;; * ) CYGWIN=no;; esac @end example Beware that the variable @code{CYGWIN} has a special meaning when running Cygwin, and should not be changed. That's yet another reason not to use this macro. @end defmac @defmac AC_DECL_SYS_SIGLIST @acindex{DECL_SYS_SIGLIST} @cvindex SYS_SIGLIST_DECLARED Same as: @example AC_CHECK_DECLS([sys_siglist], [], [], [#include /* NetBSD declares sys_siglist in unistd.h. */ #ifdef HAVE_UNISTD_H # include #endif ]) @end example @end defmac @defmac AC_DECL_YYTEXT @acindex{DECL_YYTEXT} Does nothing, now integrated in @code{AC_PROG_LEX}. @end defmac @defmac AC_DIR_HEADER @acindex{DIR_HEADER} @cvindex DIRENT @cvindex SYSNDIR @cvindex SYSDIR @cvindex NDIR Like calling @code{AC_FUNC_CLOSEDIR_VOID} and@code{AC_HEADER_DIRENT}, but defines a different set of C preprocessor macros to indicate which header file is found: @multitable {@file{sys/ndir.h}} {Old Symbol} {@code{HAVE_SYS_NDIR_H}} @item Header @tab Old Symbol @tab New Symbol @item @file{dirent.h} @tab @code{DIRENT} @tab @code{HAVE_DIRENT_H} @item @file{sys/ndir.h} @tab @code{SYSNDIR} @tab @code{HAVE_SYS_NDIR_H} @item @file{sys/dir.h} @tab @code{SYSDIR} @tab @code{HAVE_SYS_DIR_H} @item @file{ndir.h} @tab @code{NDIR} @tab @code{HAVE_NDIR_H} @end multitable @end defmac @defmac AC_DYNIX_SEQ @acindex{DYNIX_SEQ} If on DYNIX/ptx, add @option{-lseq} to output variable @code{LIBS}. This macro used to be defined as @example AC_CHECK_LIB([seq], [getmntent], [LIBS="-lseq $LIBS"]) @end example @noindent now it is just @code{AC_FUNC_GETMNTENT}. @end defmac @defmac AC_EXEEXT @acindex{EXEEXT} @ovindex EXEEXT Defined the output variable @code{EXEEXT} based on the output of the compiler, which is now done automatically. Typically set to empty string if Posix and @samp{.exe} if a @acronym{DOS} variant. @end defmac @defmac AC_EMXOS2 @acindex{EMXOS2} Similar to @code{AC_CYGWIN} but checks for the EMX environment on OS/2 and sets @code{EMXOS2}. @end defmac @defmac AC_ERROR @acindex{ERROR} @code{AC_MSG_ERROR} @end defmac @defmac AC_FIND_X @acindex{FIND_X} @code{AC_PATH_X} @end defmac @defmac AC_FIND_XTRA @acindex{FIND_XTRA} @code{AC_PATH_XTRA} @end defmac @defmac AC_FOREACH @acindex{FOREACH} @code{m4_foreach_w} @end defmac @defmac AC_FUNC_CHECK @acindex{FUNC_CHECK} @code{AC_CHECK_FUNC} @end defmac @defmac AC_FUNC_WAIT3 @acindex{FUNC_WAIT3} @cvindex HAVE_WAIT3 If @code{wait3} is found and fills in the contents of its third argument (a @samp{struct rusage *}), which @acronym{HP-UX} does not do, define @code{HAVE_WAIT3}. These days portable programs should use @code{waitpid}, not @code{wait3}, as @code{wait3} has been removed from Posix. @end defmac @defmac AC_GCC_TRADITIONAL @acindex{GCC_TRADITIONAL} @code{AC_PROG_GCC_TRADITIONAL} @end defmac @defmac AC_GETGROUPS_T @acindex{GETGROUPS_T} @code{AC_TYPE_GETGROUPS} @end defmac @defmac AC_GETLOADAVG @acindex{GETLOADAVG} @code{AC_FUNC_GETLOADAVG} @end defmac @defmac AC_HAVE_FUNCS @acindex{HAVE_FUNCS} @code{AC_CHECK_FUNCS} @end defmac @defmac AC_HAVE_HEADERS @acindex{HAVE_HEADERS} @code{AC_CHECK_HEADERS} @end defmac @defmac AC_HAVE_LIBRARY (@var{library}, @ovar{action-if-found}, @ovar{action-if-not-found}, @ovar{other-libraries}) @acindex{HAVE_LIBRARY} This macro is equivalent to calling @code{AC_CHECK_LIB} with a @var{function} argument of @code{main}. In addition, @var{library} can be written as any of @samp{foo}, @option{-lfoo}, or @samp{libfoo.a}. In all of those cases, the compiler is passed @option{-lfoo}. However, @var{library} cannot be a shell variable; it must be a literal name. @end defmac @defmac AC_HAVE_POUNDBANG @acindex{HAVE_POUNDBANG} @code{AC_SYS_INTERPRETER} (different calling convention) @end defmac @defmac AC_HEADER_CHECK @acindex{HEADER_CHECK} @code{AC_CHECK_HEADER} @end defmac @defmac AC_HEADER_EGREP @acindex{HEADER_EGREP} @code{AC_EGREP_HEADER} @end defmac @defmac AC_HELP_STRING @acindex{HELP_STRING} @code{AS_HELP_STRING} @end defmac @defmac AC_INIT (@var{unique-file-in-source-dir}) @acindex{INIT} Formerly @code{AC_INIT} used to have a single argument, and was equivalent to: @example AC_INIT AC_CONFIG_SRCDIR(@var{unique-file-in-source-dir}) @end example @end defmac @defmac AC_INLINE @acindex{INLINE} @code{AC_C_INLINE} @end defmac @defmac AC_INT_16_BITS @acindex{INT_16_BITS} @cvindex INT_16_BITS If the C type @code{int} is 16 bits wide, define @code{INT_16_BITS}. Use @samp{AC_CHECK_SIZEOF(int)} instead. @end defmac @defmac AC_IRIX_SUN @acindex{IRIX_SUN} If on @sc{irix} (Silicon Graphics Unix), add @option{-lsun} to output @code{LIBS}. If you were using it to get @code{getmntent}, use @code{AC_FUNC_GETMNTENT} instead. If you used it for the NIS versions of the password and group functions, use @samp{AC_CHECK_LIB(sun, getpwnam)}. Up to Autoconf 2.13, it used to be @example AC_CHECK_LIB([sun], [getmntent], [LIBS="-lsun $LIBS"]) @end example @noindent now it is defined as @example AC_FUNC_GETMNTENT AC_CHECK_LIB([sun], [getpwnam]) @end example @end defmac @defmac AC_LANG_C @acindex{LANG_C} Same as @samp{AC_LANG([C])}. @end defmac @defmac AC_LANG_CPLUSPLUS @acindex{LANG_CPLUSPLUS} Same as @samp{AC_LANG([C++])}. @end defmac @defmac AC_LANG_FORTRAN77 @acindex{LANG_FORTRAN77} Same as @samp{AC_LANG([Fortran 77])}. @end defmac @defmac AC_LANG_RESTORE @acindex{LANG_RESTORE} Select the @var{language} that is saved on the top of the stack, as set by @code{AC_LANG_SAVE}, remove it from the stack, and call @code{AC_LANG(@var{language})}. @end defmac @defmac AC_LANG_SAVE @acindex{LANG_SAVE} Remember the current language (as set by @code{AC_LANG}) on a stack. The current language does not change. @code{AC_LANG_PUSH} is preferred. @end defmac @defmac AC_LINK_FILES (@var{source}@dots{}, @var{dest}@dots{}) @acindex{LINK_FILES} This is an obsolete version of @code{AC_CONFIG_LINKS}. An updated version of: @example AC_LINK_FILES(config/$machine.h config/$obj_format.h, host.h object.h) @end example @noindent is: @example AC_CONFIG_LINKS([host.h:config/$machine.h object.h:config/$obj_format.h]) @end example @end defmac @defmac AC_LN_S @acindex{LN_S} @code{AC_PROG_LN_S} @end defmac @defmac AC_LONG_64_BITS @acindex{LONG_64_BITS} @cvindex LONG_64_BITS Define @code{LONG_64_BITS} if the C type @code{long int} is 64 bits wide. Use the generic macro @samp{AC_CHECK_SIZEOF([long int])} instead. @end defmac @defmac AC_LONG_DOUBLE @acindex{LONG_DOUBLE} If the C compiler supports a working @code{long double} type with more range or precision than the @code{double} type, define @code{HAVE_LONG_DOUBLE}. You should use @code{AC_TYPE_LONG_DOUBLE} or @code{AC_TYPE_LONG_DOUBLE_WIDER} instead. @xref{Particular Types}. @end defmac @defmac AC_LONG_FILE_NAMES @acindex{LONG_FILE_NAMES} @code{AC_SYS_LONG_FILE_NAMES} @end defmac @defmac AC_MAJOR_HEADER @acindex{MAJOR_HEADER} @code{AC_HEADER_MAJOR} @end defmac @defmac AC_MEMORY_H @acindex{MEMORY_H} @cvindex NEED_MEMORY_H Used to define @code{NEED_MEMORY_H} if the @code{mem} functions were defined in @file{memory.h}. Today it is equivalent to @samp{AC_CHECK_HEADERS([memory.h])}. Adjust your code to depend upon @code{HAVE_MEMORY_H}, not @code{NEED_MEMORY_H}; see @ref{Standard Symbols}. @end defmac @defmac AC_MINGW32 @acindex{MINGW32} Similar to @code{AC_CYGWIN} but checks for the MinGW compiler environment and sets @code{MINGW32}. @end defmac @defmac AC_MINUS_C_MINUS_O @acindex{MINUS_C_MINUS_O} @code{AC_PROG_CC_C_O} @end defmac @defmac AC_MMAP @acindex{MMAP} @code{AC_FUNC_MMAP} @end defmac @defmac AC_MODE_T @acindex{MODE_T} @code{AC_TYPE_MODE_T} @end defmac @defmac AC_OBJEXT @acindex{OBJEXT} @ovindex OBJEXT Defined the output variable @code{OBJEXT} based on the output of the compiler, after .c files have been excluded. Typically set to @samp{o} if Posix, @samp{obj} if a @acronym{DOS} variant. Now the compiler checking macros handle this automatically. @end defmac @defmac AC_OBSOLETE (@var{this-macro-name}, @ovar{suggestion}) @acindex{OBSOLETE} Make M4 print a message to the standard error output warning that @var{this-macro-name} is obsolete, and giving the file and line number where it was called. @var{this-macro-name} should be the name of the macro that is calling @code{AC_OBSOLETE}. If @var{suggestion} is given, it is printed at the end of the warning message; for example, it can be a suggestion for what to use instead of @var{this-macro-name}. For instance @example AC_OBSOLETE([$0], [; use AC_CHECK_HEADERS(unistd.h) instead])dnl @end example You are encouraged to use @code{AU_DEFUN} instead, since it gives better services to the user. @end defmac @defmac AC_OFF_T @acindex{OFF_T} @code{AC_TYPE_OFF_T} @end defmac @defmac AC_OUTPUT (@ovar{file}@dots{}, @ovar{extra-cmds}, @ovar{init-cmds}) @acindex{OUTPUT} The use of @code{AC_OUTPUT} with argument is deprecated. This obsoleted interface is equivalent to: @example @group AC_CONFIG_FILES(@var{file}@dots{}) AC_CONFIG_COMMANDS([default], @var{extra-cmds}, @var{init-cmds}) AC_OUTPUT @end group @end example @end defmac @defmac AC_OUTPUT_COMMANDS (@var{extra-cmds}, @ovar{init-cmds}) @acindex{OUTPUT_COMMANDS} Specify additional shell commands to run at the end of @file{config.status}, and shell commands to initialize any variables from @command{configure}. This macro may be called multiple times. It is obsolete, replaced by @code{AC_CONFIG_COMMANDS}. Here is an unrealistic example: @example fubar=27 AC_OUTPUT_COMMANDS([echo this is extra $fubar, and so on.], [fubar=$fubar]) AC_OUTPUT_COMMANDS([echo this is another, extra, bit], [echo init bit]) @end example Aside from the fact that @code{AC_CONFIG_COMMANDS} requires an additional key, an important difference is that @code{AC_OUTPUT_COMMANDS} is quoting its arguments twice, unlike @code{AC_CONFIG_COMMANDS}. This means that @code{AC_CONFIG_COMMANDS} can safely be given macro calls as arguments: @example AC_CONFIG_COMMANDS(foo, [my_FOO()]) @end example @noindent Conversely, where one level of quoting was enough for literal strings with @code{AC_OUTPUT_COMMANDS}, you need two with @code{AC_CONFIG_COMMANDS}. The following lines are equivalent: @example @group AC_OUTPUT_COMMANDS([echo "Square brackets: []"]) AC_CONFIG_COMMANDS([default], [[echo "Square brackets: []"]]) @end group @end example @end defmac @defmac AC_PID_T @acindex{PID_T} @code{AC_TYPE_PID_T} @end defmac @defmac AC_PREFIX @acindex{PREFIX} @code{AC_PREFIX_PROGRAM} @end defmac @defmac AC_PROGRAMS_CHECK @acindex{PROGRAMS_CHECK} @code{AC_CHECK_PROGS} @end defmac @defmac AC_PROGRAMS_PATH @acindex{PROGRAMS_PATH} @code{AC_PATH_PROGS} @end defmac @defmac AC_PROGRAM_CHECK @acindex{PROGRAM_CHECK} @code{AC_CHECK_PROG} @end defmac @defmac AC_PROGRAM_EGREP @acindex{PROGRAM_EGREP} @code{AC_EGREP_CPP} @end defmac @defmac AC_PROGRAM_PATH @acindex{PROGRAM_PATH} @code{AC_PATH_PROG} @end defmac @defmac AC_REMOTE_TAPE @acindex{REMOTE_TAPE} removed because of limited usefulness @end defmac @defmac AC_RESTARTABLE_SYSCALLS @acindex{RESTARTABLE_SYSCALLS} @code{AC_SYS_RESTARTABLE_SYSCALLS} @end defmac @defmac AC_RETSIGTYPE @acindex{RETSIGTYPE} @code{AC_TYPE_SIGNAL} @end defmac @defmac AC_RSH @acindex{RSH} removed because of limited usefulness @end defmac @defmac AC_SCO_INTL @acindex{SCO_INTL} @ovindex LIBS If on SCO Unix, add @option{-lintl} to output variable @code{LIBS}. This macro used to do this: @example AC_CHECK_LIB([intl], [strftime], [LIBS="-lintl $LIBS"]) @end example @noindent Now it just calls @code{AC_FUNC_STRFTIME} instead. @end defmac @defmac AC_SETVBUF_REVERSED @acindex{SETVBUF_REVERSED} @code{AC_FUNC_SETVBUF_REVERSED} @end defmac @defmac AC_SET_MAKE @acindex{SET_MAKE} @code{AC_PROG_MAKE_SET} @end defmac @defmac AC_SIZEOF_TYPE @acindex{SIZEOF_TYPE} @code{AC_CHECK_SIZEOF} @end defmac @defmac AC_SIZE_T @acindex{SIZE_T} @code{AC_TYPE_SIZE_T} @end defmac @defmac AC_STAT_MACROS_BROKEN @acindex{STAT_MACROS_BROKEN} @code{AC_HEADER_STAT} @end defmac @defmac AC_STDC_HEADERS @acindex{STDC_HEADERS} @code{AC_HEADER_STDC} @end defmac @defmac AC_STRCOLL @acindex{STRCOLL} @code{AC_FUNC_STRCOLL} @end defmac @defmac AC_ST_BLKSIZE @acindex{ST_BLKSIZE} @code{AC_CHECK_MEMBERS} @end defmac @defmac AC_ST_BLOCKS @acindex{ST_BLOCKS} @code{AC_STRUCT_ST_BLOCKS} @end defmac @defmac AC_ST_RDEV @acindex{ST_RDEV} @code{AC_CHECK_MEMBERS} @end defmac @defmac AC_SYS_RESTARTABLE_SYSCALLS @acindex{SYS_RESTARTABLE_SYSCALLS} @cvindex HAVE_RESTARTABLE_SYSCALLS If the system automatically restarts a system call that is interrupted by a signal, define @code{HAVE_RESTARTABLE_SYSCALLS}. This macro does not check whether system calls are restarted in general---it checks whether a signal handler installed with @code{signal} (but not @code{sigaction}) causes system calls to be restarted. It does not check whether system calls can be restarted when interrupted by signals that have no handler. These days portable programs should use @code{sigaction} with @code{SA_RESTART} if they want restartable system calls. They should not rely on @code{HAVE_RESTARTABLE_SYSCALLS}, since nowadays whether a system call is restartable is a dynamic issue, not a configuration-time issue. @end defmac @defmac AC_SYS_SIGLIST_DECLARED @acindex{SYS_SIGLIST_DECLARED} @code{AC_DECL_SYS_SIGLIST} @end defmac @defmac AC_TEST_CPP @acindex{TEST_CPP} @code{AC_TRY_CPP}, replaced by @code{AC_PREPROC_IFELSE}. @end defmac @defmac AC_TEST_PROGRAM @acindex{TEST_PROGRAM} @code{AC_TRY_RUN}, replaced by @code{AC_RUN_IFELSE}. @end defmac @defmac AC_TIMEZONE @acindex{TIMEZONE} @code{AC_STRUCT_TIMEZONE} @end defmac @defmac AC_TIME_WITH_SYS_TIME @acindex{TIME_WITH_SYS_TIME} @code{AC_HEADER_TIME} @end defmac @defmac AC_TRY_COMPILE (@var{includes}, @var{function-body}, @ovar{action-if-true}, @ovar{action-if-false}) @acindex{TRY_COMPILE} Same as: @example AC_COMPILE_IFELSE( [AC_LANG_PROGRAM([[@var{includes}]], [[@var{function-body}]])], [@var{action-if-true}], [@var{action-if-false}]) @end example @noindent @xref{Running the Compiler}. This macro double quotes both @var{includes} and @var{function-body}. For C and C++, @var{includes} is any @code{#include} statements needed by the code in @var{function-body} (@var{includes} is ignored if the currently selected language is Fortran or Fortran 77). The compiler and compilation flags are determined by the current language (@pxref{Language Choice}). @end defmac @defmac AC_TRY_CPP (@var{input}, @ovar{action-if-true}, @ovar{action-if-false}) @acindex{TRY_CPP} Same as: @example AC_PREPROC_IFELSE( [AC_LANG_SOURCE([[@var{input}]])], [@var{action-if-true}], [@var{action-if-false}]) @end example @noindent @xref{Running the Preprocessor}. This macro double quotes the @var{input}. @end defmac @defmac AC_TRY_LINK (@var{includes}, @var{function-body}, @ovar{action-if-true}, @ovar{action-if-false}) @acindex{TRY_LINK} Same as: @example AC_LINK_IFELSE( [AC_LANG_PROGRAM([[@var{includes}]], [[@var{function-body}]])], [@var{action-if-true}], [@var{action-if-false}]) @end example @noindent @xref{Running the Compiler}. This macro double quotes both @var{includes} and @var{function-body}. Depending on the current language (@pxref{Language Choice}), create a test program to see whether a function whose body consists of @var{function-body} can be compiled and linked. If the file compiles and links successfully, run shell commands @var{action-if-found}, otherwise run @var{action-if-not-found}. This macro double quotes both @var{includes} and @var{function-body}. For C and C++, @var{includes} is any @code{#include} statements needed by the code in @var{function-body} (@var{includes} is ignored if the currently selected language is Fortran or Fortran 77). The compiler and compilation flags are determined by the current language (@pxref{Language Choice}), and in addition @code{LDFLAGS} and @code{LIBS} are used for linking. @end defmac @defmac AC_TRY_LINK_FUNC (@var{function}, @ovar{action-if-found}, @ovar{action-if-not-found}) @acindex{TRY_LINK_FUNC} This macro is equivalent to @samp{AC_LINK_IFELSE([AC_LANG_CALL([], [@var{function}])], [@var{action-if-found}], [@var{action-if-not-found}])}. @end defmac @defmac AC_TRY_RUN (@var{program}, @ovar{action-if-true}, @ovar{action-if-false}, @ovar{action-if-cross-compiling}) @acindex{TRY_RUN} Same as: @example AC_RUN_IFELSE( [AC_LANG_SOURCE([[@var{program}]])], [@var{action-if-true}], [@var{action-if-false}], [@var{action-if-cross-compiling}]) @end example @noindent @xref{Runtime}. @end defmac @defmac AC_UID_T @acindex{UID_T} @code{AC_TYPE_UID_T} @end defmac @defmac AC_UNISTD_H @acindex{UNISTD_H} Same as @samp{AC_CHECK_HEADERS([unistd.h])}. @end defmac @defmac AC_USG @acindex{USG} @cvindex USG Define @code{USG} if the @acronym{BSD} string functions are defined in @file{strings.h}. You should no longer depend upon @code{USG}, but on @code{HAVE_STRING_H}; see @ref{Standard Symbols}. @end defmac @defmac AC_UTIME_NULL @acindex{UTIME_NULL} @code{AC_FUNC_UTIME_NULL} @end defmac @defmac AC_VALIDATE_CACHED_SYSTEM_TUPLE (@ovar{cmd}) @acindex{VALIDATE_CACHED_SYSTEM_TUPLE} If the cache file is inconsistent with the current host, target and build system types, it used to execute @var{cmd} or print a default error message. This is now handled by default. @end defmac @defmac AC_VERBOSE (@var{result-description}) @acindex{VERBOSE} @code{AC_MSG_RESULT}. @end defmac @defmac AC_VFORK @acindex{VFORK} @code{AC_FUNC_VFORK} @end defmac @defmac AC_VPRINTF @acindex{VPRINTF} @code{AC_FUNC_VPRINTF} @end defmac @defmac AC_WAIT3 @acindex{WAIT3} @code{AC_FUNC_WAIT3} @end defmac @defmac AC_WARN @acindex{WARN} @code{AC_MSG_WARN} @end defmac @defmac AC_WORDS_BIGENDIAN @acindex{WORDS_BIGENDIAN} @code{AC_C_BIGENDIAN} @end defmac @defmac AC_XENIX_DIR @acindex{XENIX_DIR} @ovindex LIBS This macro used to add @option{-lx} to output variable @code{LIBS} if on Xenix. Also, if @file{dirent.h} is being checked for, added @option{-ldir} to @code{LIBS}. Now it is merely an alias of @code{AC_HEADER_DIRENT} instead, plus some code to detect whether running @sc{xenix} on which you should not depend: @example AC_MSG_CHECKING([for Xenix]) AC_EGREP_CPP([yes], [#if defined M_XENIX && !defined M_UNIX yes #endif], [AC_MSG_RESULT([yes]); XENIX=yes], [AC_MSG_RESULT([no]); XENIX=]) @end example @end defmac @defmac AC_YYTEXT_POINTER @acindex{YYTEXT_POINTER} @code{AC_DECL_YYTEXT} @end defmac @node Autoconf 1 @section Upgrading From Version 1 @cindex Upgrading autoconf @cindex Autoconf upgrading Autoconf version 2 is mostly backward compatible with version 1. However, it introduces better ways to do some things, and doesn't support some of the ugly things in version 1. So, depending on how sophisticated your @file{configure.ac} files are, you might have to do some manual work in order to upgrade to version 2. This chapter points out some problems to watch for when upgrading. Also, perhaps your @command{configure} scripts could benefit from some of the new features in version 2; the changes are summarized in the file @file{NEWS} in the Autoconf distribution. @menu * Changed File Names:: Files you might rename * Changed Makefiles:: New things to put in @file{Makefile.in} * Changed Macros:: Macro calls you might replace * Changed Results:: Changes in how to check test results * Changed Macro Writing:: Better ways to write your own macros @end menu @node Changed File Names @subsection Changed File Names If you have an @file{aclocal.m4} installed with Autoconf (as opposed to in a particular package's source directory), you must rename it to @file{acsite.m4}. @xref{autoconf Invocation}. If you distribute @file{install.sh} with your package, rename it to @file{install-sh} so @code{make} builtin rules don't inadvertently create a file called @file{install} from it. @code{AC_PROG_INSTALL} looks for the script under both names, but it is best to use the new name. If you were using @file{config.h.top}, @file{config.h.bot}, or @file{acconfig.h}, you still can, but you have less clutter if you use the @code{AH_} macros. @xref{Autoheader Macros}. @node Changed Makefiles @subsection Changed Makefiles Add @samp{@@CFLAGS@@}, @samp{@@CPPFLAGS@@}, and @samp{@@LDFLAGS@@} in your @file{Makefile.in} files, so they can take advantage of the values of those variables in the environment when @command{configure} is run. Doing this isn't necessary, but it's a convenience for users. Also add @samp{@@configure_input@@} in a comment to each input file for @code{AC_OUTPUT}, so that the output files contain a comment saying they were produced by @command{configure}. Automatically selecting the right comment syntax for all the kinds of files that people call @code{AC_OUTPUT} on became too much work. Add @file{config.log} and @file{config.cache} to the list of files you remove in @code{distclean} targets. If you have the following in @file{Makefile.in}: @example prefix = /usr/local exec_prefix = $(prefix) @end example @noindent you must change it to: @example prefix = @@prefix@@ exec_prefix = @@exec_prefix@@ @end example @noindent The old behavior of replacing those variables without @samp{@@} characters around them has been removed. @node Changed Macros @subsection Changed Macros Many of the macros were renamed in Autoconf version 2. You can still use the old names, but the new ones are clearer, and it's easier to find the documentation for them. @xref{Obsolete Macros}, for a table showing the new names for the old macros. Use the @command{autoupdate} program to convert your @file{configure.ac} to using the new macro names. @xref{autoupdate Invocation}. Some macros have been superseded by similar ones that do the job better, but are not call-compatible. If you get warnings about calling obsolete macros while running @command{autoconf}, you may safely ignore them, but your @command{configure} script generally works better if you follow the advice that is printed about what to replace the obsolete macros with. In particular, the mechanism for reporting the results of tests has changed. If you were using @command{echo} or @code{AC_VERBOSE} (perhaps via @code{AC_COMPILE_CHECK}), your @command{configure} script's output looks better if you switch to @code{AC_MSG_CHECKING} and @code{AC_MSG_RESULT}. @xref{Printing Messages}. Those macros work best in conjunction with cache variables. @xref{Caching Results}. @node Changed Results @subsection Changed Results If you were checking the results of previous tests by examining the shell variable @code{DEFS}, you need to switch to checking the values of the cache variables for those tests. @code{DEFS} no longer exists while @command{configure} is running; it is only created when generating output files. This difference from version 1 is because properly quoting the contents of that variable turned out to be too cumbersome and inefficient to do every time @code{AC_DEFINE} is called. @xref{Cache Variable Names}. For example, here is a @file{configure.ac} fragment written for Autoconf version 1: @example AC_HAVE_FUNCS(syslog) case "$DEFS" in *-DHAVE_SYSLOG*) ;; *) # syslog is not in the default libraries. See if it's in some other. saved_LIBS="$LIBS" for lib in bsd socket inet; do AC_CHECKING(for syslog in -l$lib) LIBS="-l$lib $saved_LIBS" AC_HAVE_FUNCS(syslog) case "$DEFS" in *-DHAVE_SYSLOG*) break ;; *) ;; esac LIBS="$saved_LIBS" done ;; esac @end example Here is a way to write it for version 2: @example AC_CHECK_FUNCS([syslog]) if test $ac_cv_func_syslog = no; then # syslog is not in the default libraries. See if it's in some other. for lib in bsd socket inet; do AC_CHECK_LIB([$lib], [syslog], [AC_DEFINE([HAVE_SYSLOG]) LIBS="-l$lib $LIBS"; break]) done fi @end example If you were working around bugs in @code{AC_DEFINE_UNQUOTED} by adding backslashes before quotes, you need to remove them. It now works predictably, and does not treat quotes (except back quotes) specially. @xref{Setting Output Variables}. All of the Boolean shell variables set by Autoconf macros now use @samp{yes} for the true value. Most of them use @samp{no} for false, though for backward compatibility some use the empty string instead. If you were relying on a shell variable being set to something like 1 or @samp{t} for true, you need to change your tests. @node Changed Macro Writing @subsection Changed Macro Writing When defining your own macros, you should now use @code{AC_DEFUN} instead of @code{define}. @code{AC_DEFUN} automatically calls @code{AC_PROVIDE} and ensures that macros called via @code{AC_REQUIRE} do not interrupt other macros, to prevent nested @samp{checking@dots{}} messages on the screen. There's no actual harm in continuing to use the older way, but it's less convenient and attractive. @xref{Macro Definitions}. You probably looked at the macros that came with Autoconf as a guide for how to do things. It would be a good idea to take a look at the new versions of them, as the style is somewhat improved and they take advantage of some new features. If you were doing tricky things with undocumented Autoconf internals (macros, variables, diversions), check whether you need to change anything to account for changes that have been made. Perhaps you can even use an officially supported technique in version 2 instead of kludging. Or perhaps not. To speed up your locally written feature tests, add caching to them. See whether any of your tests are of general enough usefulness to encapsulate them into macros that you can share. @node Autoconf 2.13 @section Upgrading From Version 2.13 @cindex Upgrading autoconf @cindex Autoconf upgrading The introduction of the previous section (@pxref{Autoconf 1}) perfectly suits this section@enddots{} @quotation Autoconf version 2.50 is mostly backward compatible with version 2.13. However, it introduces better ways to do some things, and doesn't support some of the ugly things in version 2.13. So, depending on how sophisticated your @file{configure.ac} files are, you might have to do some manual work in order to upgrade to version 2.50. This chapter points out some problems to watch for when upgrading. Also, perhaps your @command{configure} scripts could benefit from some of the new features in version 2.50; the changes are summarized in the file @file{NEWS} in the Autoconf distribution. @end quotation @menu * Changed Quotation:: Broken code which used to work * New Macros:: Interaction with foreign macros * Hosts and Cross-Compilation:: Bugward compatibility kludges * AC_LIBOBJ vs LIBOBJS:: LIBOBJS is a forbidden token * AC_FOO_IFELSE vs AC_TRY_FOO:: A more generic scheme for testing sources @end menu @node Changed Quotation @subsection Changed Quotation The most important changes are invisible to you: the implementation of most macros have completely changed. This allowed more factorization of the code, better error messages, a higher uniformity of the user's interface etc. Unfortunately, as a side effect, some construct which used to (miraculously) work might break starting with Autoconf 2.50. The most common culprit is bad quotation. For instance, in the following example, the message is not properly quoted: @example AC_INIT AC_CHECK_HEADERS(foo.h, , AC_MSG_ERROR(cannot find foo.h, bailing out)) AC_OUTPUT @end example @noindent Autoconf 2.13 simply ignores it: @example $ @kbd{autoconf-2.13; ./configure --silent} creating cache ./config.cache configure: error: cannot find foo.h $ @end example @noindent while Autoconf 2.50 produces a broken @file{configure}: @example $ @kbd{autoconf-2.50; ./configure --silent} configure: error: cannot find foo.h ./configure: exit: bad non-numeric arg `bailing' ./configure: exit: bad non-numeric arg `bailing' $ @end example The message needs to be quoted, and the @code{AC_MSG_ERROR} invocation too! @example AC_INIT([Example], [1.0], [bug-example@@example.org]) AC_CHECK_HEADERS([foo.h], [], [AC_MSG_ERROR([cannot find foo.h, bailing out])]) AC_OUTPUT @end example Many many (and many more) Autoconf macros were lacking proper quotation, including no less than@dots{} @code{AC_DEFUN} itself! @example $ @kbd{cat configure.in} AC_DEFUN([AC_PROG_INSTALL], [# My own much better version ]) AC_INIT AC_PROG_INSTALL AC_OUTPUT $ @kbd{autoconf-2.13} autoconf: Undefined macros: ***BUG in Autoconf--please report*** AC_FD_MSG ***BUG in Autoconf--please report*** AC_EPI configure.in:1:AC_DEFUN([AC_PROG_INSTALL], configure.in:5:AC_PROG_INSTALL $ @kbd{autoconf-2.50} $ @end example @node New Macros @subsection New Macros @cindex undefined macro @cindex @code{_m4_divert_diversion} While Autoconf was relatively dormant in the late 1990s, Automake provided Autoconf-like macros for a while. Starting with Autoconf 2.50 in 2001, Autoconf provided versions of these macros, integrated in the @code{AC_} namespace, instead of @code{AM_}. But in order to ease the upgrading via @command{autoupdate}, bindings to such @code{AM_} macros are provided. Unfortunately older versions of Automake (e.g., Automake 1.4) did not quote the names of these macros. Therefore, when @command{m4} finds something like @samp{AC_DEFUN(AM_TYPE_PTRDIFF_T, @dots{})} in @file{aclocal.m4}, @code{AM_TYPE_PTRDIFF_T} is expanded, replaced with its Autoconf definition. Fortunately Autoconf catches pre-@code{AC_INIT} expansions, and complains, in its own words: @example $ @kbd{cat configure.ac} AC_INIT([Example], [1.0], [bug-example@@example.org]) AM_TYPE_PTRDIFF_T $ @kbd{aclocal-1.4} $ @kbd{autoconf} aclocal.m4:17: error: m4_defn: undefined macro: _m4_divert_diversion aclocal.m4:17: the top level autom4te: m4 failed with exit status: 1 $ @end example Modern versions of Automake no longer define most of these macros, and properly quote the names of the remaining macros. If you must use an old Automake, do not depend upon macros from Automake as it is simply not its job to provide macros (but the one it requires itself): @example $ @kbd{cat configure.ac} AC_INIT([Example], [1.0], [bug-example@@example.org]) AM_TYPE_PTRDIFF_T $ @kbd{rm aclocal.m4} $ @kbd{autoupdate} autoupdate: `configure.ac' is updated $ @kbd{cat configure.ac} AC_INIT([Example], [1.0], [bug-example@@example.org]) AC_CHECK_TYPES([ptrdiff_t]) $ @kbd{aclocal-1.4} $ @kbd{autoconf} $ @end example @node Hosts and Cross-Compilation @subsection Hosts and Cross-Compilation @cindex Cross compilation Based on the experience of compiler writers, and after long public debates, many aspects of the cross-compilation chain have changed: @itemize @minus @item the relationship between the build, host, and target architecture types, @item the command line interface for specifying them to @command{configure}, @item the variables defined in @command{configure}, @item the enabling of cross-compilation mode. @end itemize @sp 1 The relationship between build, host, and target have been cleaned up: the chain of default is now simply: target defaults to host, host to build, and build to the result of @command{config.guess}. Nevertheless, in order to ease the transition from 2.13 to 2.50, the following transition scheme is implemented. @emph{Do not rely on it}, as it will be completely disabled in a couple of releases (we cannot keep it, as it proves to cause more problems than it cures). They all default to the result of running @command{config.guess}, unless you specify either @option{--build} or @option{--host}. In this case, the default becomes the system type you specified. If you specify both, and they're different, @command{configure} enters cross compilation mode, so it doesn't run any tests that require execution. Hint: if you mean to override the result of @command{config.guess}, prefer @option{--build} over @option{--host}. In the future, @option{--host} will not override the name of the build system type. Whenever you specify @option{--host}, be sure to specify @option{--build} too. @sp 1 For backward compatibility, @command{configure} accepts a system type as an option by itself. Such an option overrides the defaults for build, host, and target system types. The following configure statement configures a cross toolchain that runs on Net@acronym{BSD}/alpha but generates code for @acronym{GNU} Hurd/sparc, which is also the build platform. @example ./configure --host=alpha-netbsd sparc-gnu @end example @sp 1 In Autoconf 2.13 and before, the variables @code{build}, @code{host}, and @code{target} had a different semantics before and after the invocation of @code{AC_CANONICAL_BUILD} etc. Now, the argument of @option{--build} is strictly copied into @code{build_alias}, and is left empty otherwise. After the @code{AC_CANONICAL_BUILD}, @code{build} is set to the canonicalized build type. To ease the transition, before, its contents is the same as that of @code{build_alias}. Do @emph{not} rely on this broken feature. For consistency with the backward compatibility scheme exposed above, when @option{--host} is specified but @option{--build} isn't, the build system is assumed to be the same as @option{--host}, and @samp{build_alias} is set to that value. Eventually, this historically incorrect behavior will go away. @sp 1 The former scheme to enable cross-compilation proved to cause more harm than good, in particular, it used to be triggered too easily, leaving regular end users puzzled in front of cryptic error messages. @command{configure} could even enter cross-compilation mode only because the compiler was not functional. This is mainly because @command{configure} used to try to detect cross-compilation, instead of waiting for an explicit flag from the user. Now, @command{configure} enters cross-compilation mode if and only if @option{--host} is passed. That's the short documentation. To ease the transition between 2.13 and its successors, a more complicated scheme is implemented. @emph{Do not rely on the following}, as it will be removed in the near future. If you specify @option{--host}, but not @option{--build}, when @command{configure} performs the first compiler test it tries to run an executable produced by the compiler. If the execution fails, it enters cross-compilation mode. This is fragile. Moreover, by the time the compiler test is performed, it may be too late to modify the build-system type: other tests may have already been performed. Therefore, whenever you specify @option{--host}, be sure to specify @option{--build} too. @example ./configure --build=i686-pc-linux-gnu --host=m68k-coff @end example @noindent enters cross-compilation mode. The former interface, which consisted in setting the compiler to a cross-compiler without informing @command{configure} is obsolete. For instance, @command{configure} fails if it can't run the code generated by the specified compiler if you configure as follows: @example ./configure CC=m68k-coff-gcc @end example @node AC_LIBOBJ vs LIBOBJS @subsection @code{AC_LIBOBJ} vs.@: @code{LIBOBJS} Up to Autoconf 2.13, the replacement of functions was triggered via the variable @code{LIBOBJS}. Since Autoconf 2.50, the macro @code{AC_LIBOBJ} should be used instead (@pxref{Generic Functions}). Starting at Autoconf 2.53, the use of @code{LIBOBJS} is an error. This change is mandated by the unification of the @acronym{GNU} Build System components. In particular, the various fragile techniques used to parse a @file{configure.ac} are all replaced with the use of traces. As a consequence, any action must be traceable, which obsoletes critical variable assignments. Fortunately, @code{LIBOBJS} was the only problem, and it can even be handled gracefully (read, ``without your having to change something''). There were two typical uses of @code{LIBOBJS}: asking for a replacement function, and adjusting @code{LIBOBJS} for Automake and/or Libtool. @sp 1 As for function replacement, the fix is immediate: use @code{AC_LIBOBJ}. For instance: @example LIBOBJS="$LIBOBJS fnmatch.o" LIBOBJS="$LIBOBJS malloc.$ac_objext" @end example @noindent should be replaced with: @example AC_LIBOBJ([fnmatch]) AC_LIBOBJ([malloc]) @end example @sp 1 @ovindex LIBOBJDIR When used with Automake 1.10 or newer, a suitable value for @code{LIBOBJDIR} is set so that the @code{LIBOBJS} and @code{LTLIBOBJS} can be referenced from any @file{Makefile.am}. Even without Automake, arranging for @code{LIBOBJDIR} to be set correctly enables referencing @code{LIBOBJS} and @code{LTLIBOBJS} in another directory. The @code{LIBOJBDIR} feature is experimental. @node AC_FOO_IFELSE vs AC_TRY_FOO @subsection @code{AC_FOO_IFELSE} vs.@: @code{AC_TRY_FOO} Since Autoconf 2.50, internal codes uses @code{AC_PREPROC_IFELSE}, @code{AC_COMPILE_IFELSE}, @code{AC_LINK_IFELSE}, and @code{AC_RUN_IFELSE} on one hand and @code{AC_LANG_SOURCES}, and @code{AC_LANG_PROGRAM} on the other hand instead of the deprecated @code{AC_TRY_CPP}, @code{AC_TRY_COMPILE}, @code{AC_TRY_LINK}, and @code{AC_TRY_RUN}. The motivations where: @itemize @minus @item a more consistent interface: @code{AC_TRY_COMPILE} etc.@: were double quoting their arguments; @item the combinatoric explosion is solved by decomposing on the one hand the generation of sources, and on the other hand executing the program; @item this scheme helps supporting more languages than plain C and C++. @end itemize In addition to the change of syntax, the philosophy has changed too: while emphasis was put on speed at the expense of accuracy, today's Autoconf promotes accuracy of the testing framework at, ahem@dots{}, the expense of speed. As a perfect example of what is @emph{not} to be done, here is how to find out whether a header file contains a particular declaration, such as a typedef, a structure, a structure member, or a function. Use @code{AC_EGREP_HEADER} instead of running @code{grep} directly on the header file; on some systems the symbol might be defined in another header file that the file you are checking includes. As a (bad) example, here is how you should not check for C preprocessor symbols, either defined by header files or predefined by the C preprocessor: using @code{AC_EGREP_CPP}: @example @group AC_EGREP_CPP(yes, [#ifdef _AIX yes #endif ], is_aix=yes, is_aix=no) @end group @end example The above example, properly written would (i) use @code{AC_LANG_PROGRAM}, and (ii) run the compiler: @example @group AC_COMPILE_IFELSE([AC_LANG_PROGRAM( [[#ifndef _AIX error: This isn't AIX! #endif ]])], [is_aix=yes], [is_aix=no]) @end group @end example @c ============================= Generating Test Suites with Autotest @node Using Autotest @chapter Generating Test Suites with Autotest @cindex Autotest @display @strong{N.B.: This section describes an experimental feature which will be part of Autoconf in a forthcoming release. Although we believe Autotest is stabilizing, this documentation describes an interface which might change in the future: do not depend upon Autotest without subscribing to the Autoconf mailing lists.} @end display It is paradoxical that portable projects depend on nonportable tools to run their test suite. Autoconf by itself is the paragon of this problem: although it aims at perfectly portability, up to 2.13 its test suite was using Deja@acronym{GNU}, a rich and complex testing framework, but which is far from being standard on Posix systems. Worse yet, it was likely to be missing on the most fragile platforms, the very platforms that are most likely to torture Autoconf and exhibit deficiencies. To circumvent this problem, many package maintainers have developed their own testing framework, based on simple shell scripts whose sole outputs are exit status values describing whether the test succeeded. Most of these tests share common patterns, and this can result in lots of duplicated code and tedious maintenance. Following exactly the same reasoning that yielded to the inception of Autoconf, Autotest provides a test suite generation framework, based on M4 macros building a portable shell script. The suite itself is equipped with automatic logging and tracing facilities which greatly diminish the interaction with bug reporters, and simple timing reports. Autoconf itself has been using Autotest for years, and we do attest that it has considerably improved the strength of the test suite and the quality of bug reports. Other projects are known to use some generation of Autotest, such as Bison, Free Recode, Free Wdiff, @acronym{GNU} Tar, each of them with different needs, and this usage has validated Autotest as a general testing framework. Nonetheless, compared to Deja@acronym{GNU}, Autotest is inadequate for interactive tool testing, which is probably its main limitation. @menu * Using an Autotest Test Suite:: Autotest and the user * Writing testsuite.at:: Autotest macros * testsuite Invocation:: Running @command{testsuite} scripts * Making testsuite Scripts:: Using autom4te to create @command{testsuite} @end menu @node Using an Autotest Test Suite @section Using an Autotest Test Suite @menu * testsuite Scripts:: The concepts of Autotest * Autotest Logs:: Their contents @end menu @node testsuite Scripts @subsection @command{testsuite} Scripts @cindex @command{testsuite} Generating testing or validation suites using Autotest is rather easy. The whole validation suite is held in a file to be processed through @command{autom4te}, itself using @acronym{GNU} M4 under the scene, to produce a stand-alone Bourne shell script which then gets distributed. Neither @command{autom4te} nor @acronym{GNU} M4 are needed at the installer's end. @cindex test group Each test of the validation suite should be part of some test group. A @dfn{test group} is a sequence of interwoven tests that ought to be executed together, usually because one test in the group creates data files than a later test in the same group needs to read. Complex test groups make later debugging more tedious. It is much better to keep only a few tests per test group. Ideally there is only one test per test group. For all but the simplest packages, some file such as @file{testsuite.at} does not fully hold all test sources, as these are often easier to maintain in separate files. Each of these separate files holds a single test group, or a sequence of test groups all addressing some common functionality in the package. In such cases, @file{testsuite.at} merely initializes the validation suite, and sometimes does elementary health checking, before listing include statements for all other test files. The special file @file{package.m4}, containing the identification of the package, is automatically included if found. A convenient alternative consists in moving all the global issues (local Autotest macros, elementary health checking, and @code{AT_INIT} invocation) into the file @code{local.at}, and making @file{testsuite.at} be a simple list of @code{m4_include} of sub test suites. In such case, generating the whole test suite or pieces of it is only a matter of choosing the @command{autom4te} command line arguments. The validation scripts that Autotest produces are by convention called @command{testsuite}. When run, @command{testsuite} executes each test group in turn, producing only one summary line per test to say if that particular test succeeded or failed. At end of all tests, summarizing counters get printed. One debugging directory is left for each test group which failed, if any: such directories are named @file{testsuite.dir/@var{nn}}, where @var{nn} is the sequence number of the test group, and they include: @itemize @bullet @item a debugging script named @file{run} which reruns the test in @dfn{debug mode} (@pxref{testsuite Invocation}). The automatic generation of debugging scripts has the purpose of easing the chase for bugs. @item all the files created with @code{AT_DATA} @item a log of the run, named @file{testsuite.log} @end itemize In the ideal situation, none of the tests fail, and consequently no debugging directory is left behind for validation. It often happens in practice that individual tests in the validation suite need to get information coming out of the configuration process. Some of this information, common for all validation suites, is provided through the file @file{atconfig}, automatically created by @code{AC_CONFIG_TESTDIR}. For configuration informations which your testing environment specifically needs, you might prepare an optional file named @file{atlocal.in}, instantiated by @code{AC_CONFIG_FILES}. The configuration process produces @file{atconfig} and @file{atlocal} out of these two input files, and these two produced files are automatically read by the @file{testsuite} script. Here is a diagram showing the relationship between files. @noindent Files used in preparing a software package for distribution: @example [package.m4] -->. \ subfile-1.at ->. [local.at] ---->+ ... \ \ subfile-i.at ---->-- testsuite.at -->-- autom4te* -->testsuite ... / subfile-n.at ->' @end example @noindent Files used in configuring a software package: @example .--> atconfig / [atlocal.in] --> config.status* --< \ `--> [atlocal] @end example @noindent Files created during the test suite execution: @example atconfig -->. .--> testsuite.log \ / >-- testsuite* --< / \ [atlocal] ->' `--> [testsuite.dir] @end example @node Autotest Logs @subsection Autotest Logs When run, the test suite creates a log file named after itself, e.g., a test suite named @command{testsuite} creates @file{testsuite.log}. It contains a lot of information, usually more than maintainers actually need, but therefore most of the time it contains all that is needed: @table @asis @item command line arguments @c akim s/to consist in/to consist of/ A bad but unfortunately widespread habit consists of setting environment variables before the command, such as in @samp{CC=my-home-grown-cc ./testsuite}. The test suite does not know this change, hence (i) it cannot report it to you, and (ii) it cannot preserve the value of @code{CC} for subsequent runs. Autoconf faced exactly the same problem, and solved it by asking users to pass the variable definitions as command line arguments. Autotest requires this rule, too, but has no means to enforce it; the log then contains a trace of the variables that were changed by the user. @item @file{ChangeLog} excerpts The topmost lines of all the @file{ChangeLog} files found in the source hierarchy. This is especially useful when bugs are reported against development versions of the package, since the version string does not provide sufficient information to know the exact state of the sources the user compiled. Of course, this relies on the use of a @file{ChangeLog}. @item build machine Running a test suite in a cross-compile environment is not an easy task, since it would mean having the test suite run on a machine @var{build}, while running programs on a machine @var{host}. It is much simpler to run both the test suite and the programs on @var{host}, but then, from the point of view of the test suite, there remains a single environment, @var{host} = @var{build}. The log contains relevant information on the state of the build machine, including some important environment variables. @c FIXME: How about having an M4sh macro to say `hey, log the value @c of `@dots{}'? This would help both Autoconf and Autotest. @item tested programs The absolute file name and answers to @option{--version} of the tested programs (see @ref{Writing testsuite.at}, @code{AT_TESTED}). @item configuration log The contents of @file{config.log}, as created by @command{configure}, are appended. It contains the configuration flags and a detailed report on the configuration itself. @end table @node Writing testsuite.at @section Writing @file{testsuite.at} The @file{testsuite.at} is a Bourne shell script making use of special Autotest M4 macros. It often contains a call to @code{AT_INIT} near its beginning followed by one call to @code{m4_include} per source file for tests. Each such included file, or the remainder of @file{testsuite.at} if include files are not used, contain a sequence of test groups. Each test group begins with a call to @code{AT_SETUP}, then an arbitrary number of shell commands or calls to @code{AT_CHECK}, and then completes with a call to @code{AT_CLEANUP}. @defmac AT_INIT (@ovar{name}) @atindex{INIT} @c FIXME: Not clear, plus duplication of the information. Initialize Autotest. Giving a @var{name} to the test suite is encouraged if your package includes several test suites. In any case, the test suite always displays the package name and version. It also inherits the package bug report address. @end defmac @defmac AT_COPYRIGHT (@var{copyright-notice}) @atindex{COPYRIGHT} @cindex Copyright Notice State that, in addition to the Free Software Foundation's copyright on the Autotest macros, parts of your test suite are covered by @var{copyright-notice}. The @var{copyright-notice} shows up in both the head of @command{testsuite} and in @samp{testsuite --version}. @end defmac @defmac AT_TESTED (@var{executables}) @atindex{TESTED} Log the file name and answer to @option{--version} of each program in space-separated list @var{executables}. Several invocations register new executables, in other words, don't fear registering one program several times. @end defmac Autotest test suites rely on @env{PATH} to find the tested program. This avoids the need to generate absolute names of the various tools, and makes it possible to test installed programs. Therefore, knowing which programs are being exercised is crucial to understanding problems in the test suite itself, or its occasional misuses. It is a good idea to also subscribe foreign programs you depend upon, to avoid incompatible diagnostics. @sp 1 @defmac AT_SETUP (@var{test-group-name}) @atindex{SETUP} This macro starts a group of related tests, all to be executed in the same subshell. It accepts a single argument, which holds a few words (no more than about 30 or 40 characters) quickly describing the purpose of the test group being started. @end defmac @defmac AT_KEYWORDS (@var{keywords}) @atindex{KEYWORDS} Associate the space-separated list of @var{keywords} to the enclosing test group. This makes it possible to run ``slices'' of the test suite. For instance, if some of your test groups exercise some @samp{foo} feature, then using @samp{AT_KEYWORDS(foo)} lets you run @samp{./testsuite -k foo} to run exclusively these test groups. The @var{title} of the test group is automatically recorded to @code{AT_KEYWORDS}. Several invocations within a test group accumulate new keywords. In other words, don't fear registering the same keyword several times in a test group. @end defmac @defmac AT_CAPTURE_FILE (@var{file}) @atindex{CAPTURE_FILE} If the current test group fails, log the contents of @var{file}. Several identical calls within one test group have no additional effect. @end defmac @defmac AT_XFAIL_IF (@var{shell-condition}) @atindex{XFAIL_IF} Determine whether the test is expected to fail because it is a known bug (for unsupported features, you should skip the test). @var{shell-condition} is a shell expression such as a @code{test} command; you can instantiate this macro many times from within the same test group, and one of the conditions is enough to turn the test into an expected failure. @end defmac @defmac AT_CLEANUP @atindex{CLEANUP} End the current test group. @end defmac @sp 1 @defmac AT_DATA (@var{file}, @var{contents}) @atindex{DATA} Initialize an input data @var{file} with given @var{contents}. Of course, the @var{contents} have to be properly quoted between square brackets to protect against included commas or spurious M4 expansion. The contents ought to end with an end of line. @end defmac @defmac AT_CHECK (@var{commands}, @dvar{status, 0}, @dvar{stdout, }, @dvar{stderr, }, @ovar{run-if-fail}, @ovar{run-if-pass}) @atindex{CHECK} Execute a test by performing given shell @var{commands}. These commands should normally exit with @var{status}, while producing expected @var{stdout} and @var{stderr} contents. If @var{commands} exit with status 77, then the whole test group is skipped. Otherwise, if this test fails, run shell commands @var{run-if-fail} or, if this test passes, run shell commands @var{run-if-pass}. The @var{commands} @emph{must not} redirect the standard output, nor the standard error. If @var{status}, or @var{stdout}, or @var{stderr} is @samp{ignore}, then the corresponding value is not checked. The special value @samp{expout} for @var{stdout} means the expected output of the @var{commands} is the content of the file @file{expout}. If @var{stdout} is @samp{stdout}, then the standard output of the @var{commands} is available for further tests in the file @file{stdout}. Similarly for @var{stderr} with @samp{experr} and @samp{stderr}. @end defmac @node testsuite Invocation @section Running @command{testsuite} Scripts @cindex @command{testsuite} Autotest test suites support the following arguments: @table @option @item --help @itemx -h Display the list of options and exit successfully. @item --version @itemx -V Display the version of the test suite and exit successfully. @item --clean @itemx -c Remove all the files the test suite might have created and exit. Meant for @code{clean} Make targets. @item --list @itemx -l List all the tests (or only the selection), including their possible keywords. @end table @sp 1 By default all tests are performed (or described with @option{--list}) in the default environment first silently, then verbosely, but the environment, set of tests, and verbosity level can be tuned: @table @samp @item @var{variable}=@var{value} Set the environment @var{variable} to @var{value}. Use this rather than @samp{FOO=foo ./testsuite} as debugging scripts would then run in a different environment. @cindex @code{AUTOTEST_PATH} The variable @code{AUTOTEST_PATH} specifies the testing path to prepend to @env{PATH}. Relative directory names (not starting with @samp{/}) are considered to be relative to the top level of the package being built. All directories are made absolute, first starting from the top level @emph{build} tree, then from the @emph{source} tree. For instance @samp{./testsuite AUTOTEST_PATH=tests:bin} for a @file{/src/foo-1.0} source package built in @file{/tmp/foo} results in @samp{/tmp/foo/tests:/tmp/foo/bin} and then @samp{/src/foo-1.0/tests:/src/foo-1.0/bin} being prepended to @env{PATH}. @item @var{number} @itemx @var{number}-@var{number} @itemx @var{number}- @itemx -@var{number} Add the corresponding test groups, with obvious semantics, to the selection. @item --keywords=@var{keywords} @itemx -k @var{keywords} Add to the selection the test groups with title or keywords (arguments to @code{AT_SETUP} or @code{AT_KEYWORDS}) that match @emph{all} keywords of the comma separated list @var{keywords}, case-insensitively. Use @samp{!} immediately before the keyword to invert the selection for this keyword. By default, the keywords match whole words; enclose them in @samp{.*} to also match parts of words. For example, running @example @kbd{./testsuite -k 'autoupdate,.*FUNC.*'} @end example @noindent selects all tests tagged @samp{autoupdate} @emph{and} with tags containing @samp{FUNC} (as in @samp{AC_CHECK_FUNC}, @samp{AC_FUNC_ALLOCA}, etc.), while @example @kbd{./testsuite -k '!autoupdate' -k '.*FUNC.*'} @end example @noindent selects all tests not tagged @samp{autoupdate} @emph{or} with tags containing @samp{FUNC}. @item --errexit @itemx -e If any test fails, immediately abort testing. It implies @option{--debug}: post test group clean up, and top-level logging are inhibited. This option is meant for the full test suite, it is not really useful for generated debugging scripts. @item --verbose @itemx -v Force more verbosity in the detailed output of what is being done. This is the default for debugging scripts. @item --debug @itemx -d Do not remove the files after a test group was performed ---but they are still removed @emph{before}, therefore using this option is sane when running several test groups. Create debugging scripts. Do not overwrite the top-level log (in order to preserve supposedly existing full log file). This is the default for debugging scripts, but it can also be useful to debug the testsuite itself. @item --trace @itemx -x Trigger shell tracing of the test groups. @end table @node Making testsuite Scripts @section Making @command{testsuite} Scripts For putting Autotest into movement, you need some configuration and makefile machinery. We recommend, at least if your package uses deep or shallow hierarchies, that you use @file{tests/} as the name of the directory holding all your tests and their makefile. Here is a check list of things to do. @itemize @minus @item @cindex @file{package.m4} Make sure to create the file @file{package.m4}, which defines the identity of the package. It must define @code{AT_PACKAGE_STRING}, the full signature of the package, and @code{AT_PACKAGE_BUGREPORT}, the address to which bug reports should be sent. For sake of completeness, we suggest that you also define @code{AT_PACKAGE_NAME}, @code{AT_PACKAGE_TARNAME}, and @code{AT_PACKAGE_VERSION}. @xref{Initializing configure}, for a description of these variables. We suggest the following makefile excerpt: @smallexample $(srcdir)/package.m4: $(top_srcdir)/configure.ac @{ \ echo '# Signature of the current package.'; \ echo 'm4_define([AT_PACKAGE_NAME], [@@PACKAGE_NAME@@])'; \ echo 'm4_define([AT_PACKAGE_TARNAME], [@@PACKAGE_TARNAME@@])'; \ echo 'm4_define([AT_PACKAGE_VERSION], [@@PACKAGE_VERSION@@])'; \ echo 'm4_define([AT_PACKAGE_STRING], [@@PACKAGE_STRING@@])'; \ echo 'm4_define([AT_PACKAGE_BUGREPORT], [@@PACKAGE_BUGREPORT@@])'; \ @} >'$(srcdir)/package.m4' @end smallexample @noindent Be sure to distribute @file{package.m4} and to put it into the source hierarchy: the test suite ought to be shipped! @item Invoke @code{AC_CONFIG_TESTDIR}. @defmac AC_CONFIG_TESTDIR (@var{directory}, @dvar{test-path, directory}) @acindex{CONFIG_TESTDIR} An Autotest test suite is to be configured in @var{directory}. This macro requires the instantiation of @file{@var{directory}/atconfig} from @file{@var{directory}/atconfig.in}, and sets the default @code{AUTOTEST_PATH} to @var{test-path} (@pxref{testsuite Invocation}). @end defmac @item Still within @file{configure.ac}, as appropriate, ensure that some @code{AC_CONFIG_FILES} command includes substitution for @file{tests/atlocal}. @item The @file{tests/Makefile.in} should be modified so the validation in your package is triggered by @samp{make check}. An example is provided below. @end itemize With Automake, here is a minimal example about how to link @samp{make check} with a validation suite. @example EXTRA_DIST = testsuite.at $(TESTSUITE) atlocal.in TESTSUITE = $(srcdir)/testsuite check-local: atconfig atlocal $(TESTSUITE) $(SHELL) '$(TESTSUITE)' $(TESTSUITEFLAGS) installcheck-local: atconfig atlocal $(TESTSUITE) $(SHELL) '$(TESTSUITE)' AUTOTEST_PATH='$(bindir)' \ $(TESTSUITEFLAGS) clean-local: test ! -f '$(TESTSUITE)' || \ $(SHELL) '$(TESTSUITE)' --clean AUTOTEST = $(AUTOM4TE) --language=autotest $(TESTSUITE): $(srcdir)/testsuite.at $(AUTOTEST) -I '$(srcdir)' -o $@@.tmp $@@.at mv $@@.tmp $@@ @end example You might want to list explicitly the dependencies, i.e., the list of the files @file{testsuite.at} includes. With strict Autoconf, you might need to add lines inspired from the following: @example subdir = tests atconfig: $(top_builddir)/config.status cd $(top_builddir) && \ $(SHELL) ./config.status $(subdir)/$@@ atlocal: $(srcdir)/atlocal.in $(top_builddir)/config.status cd $(top_builddir) && \ $(SHELL) ./config.status $(subdir)/$@@ @end example @noindent and manage to have @file{atconfig.in} and @code{$(EXTRA_DIST)} distributed. With all this in place, and if you have not initialized @samp{TESTSUITEFLAGS} within your makefile, you can fine-tune test suite execution with this variable, for example: @example make check TESTSUITEFLAGS='-v -d -x 75 -k AC_PROG_CC CFLAGS=-g' @end example @c =============================== Frequent Autoconf Questions, with answers @node FAQ @chapter Frequent Autoconf Questions, with answers Several questions about Autoconf come up occasionally. Here some of them are addressed. @menu * Distributing:: Distributing @command{configure} scripts * Why GNU M4:: Why not use the standard M4? * Bootstrapping:: Autoconf and @acronym{GNU} M4 require each other? * Why Not Imake:: Why @acronym{GNU} uses @command{configure} instead of Imake * Defining Directories:: Passing @code{datadir} to program * autom4te.cache:: What is it? Can I remove it? * Present But Cannot Be Compiled:: Compiler and Preprocessor Disagree @end menu @node Distributing @section Distributing @command{configure} Scripts @cindex License @display What are the restrictions on distributing @command{configure} scripts that Autoconf generates? How does that affect my programs that use them? @end display There are no restrictions on how the configuration scripts that Autoconf produces may be distributed or used. In Autoconf version 1, they were covered by the @acronym{GNU} General Public License. We still encourage software authors to distribute their work under terms like those of the @acronym{GPL}, but doing so is not required to use Autoconf. Of the other files that might be used with @command{configure}, @file{config.h.in} is under whatever copyright you use for your @file{configure.ac}. @file{config.sub} and @file{config.guess} have an exception to the @acronym{GPL} when they are used with an Autoconf-generated @command{configure} script, which permits you to distribute them under the same terms as the rest of your package. @file{install-sh} is from the X Consortium and is not copyrighted. @node Why GNU M4 @section Why Require @acronym{GNU} M4? @display Why does Autoconf require @acronym{GNU} M4? @end display Many M4 implementations have hard-coded limitations on the size and number of macros that Autoconf exceeds. They also lack several builtin macros that it would be difficult to get along without in a sophisticated application like Autoconf, including: @example m4_builtin m4_indir m4_bpatsubst __file__ __line__ @end example Autoconf requires version 1.4.7 or later of @acronym{GNU} M4. Since only software maintainers need to use Autoconf, and since @acronym{GNU} M4 is simple to configure and install, it seems reasonable to require @acronym{GNU} M4 to be installed also. Many maintainers of @acronym{GNU} and other free software already have most of the @acronym{GNU} utilities installed, since they prefer them. @node Bootstrapping @section How Can I Bootstrap? @cindex Bootstrap @display If Autoconf requires @acronym{GNU} M4 and @acronym{GNU} M4 has an Autoconf @command{configure} script, how do I bootstrap? It seems like a chicken and egg problem! @end display This is a misunderstanding. Although @acronym{GNU} M4 does come with a @command{configure} script produced by Autoconf, Autoconf is not required in order to run the script and install @acronym{GNU} M4. Autoconf is only required if you want to change the M4 @command{configure} script, which few people have to do (mainly its maintainer). @node Why Not Imake @section Why Not Imake? @cindex Imake @display Why not use Imake instead of @command{configure} scripts? @end display Several people have written addressing this question, so I include adaptations of their explanations here. The following answer is based on one written by Richard Pixley: @quotation Autoconf generated scripts frequently work on machines that it has never been set up to handle before. That is, it does a good job of inferring a configuration for a new system. Imake cannot do this. Imake uses a common database of host specific data. For X11, this makes sense because the distribution is made as a collection of tools, by one central authority who has control over the database. @acronym{GNU} tools are not released this way. Each @acronym{GNU} tool has a maintainer; these maintainers are scattered across the world. Using a common database would be a maintenance nightmare. Autoconf may appear to be this kind of database, but in fact it is not. Instead of listing host dependencies, it lists program requirements. If you view the @acronym{GNU} suite as a collection of native tools, then the problems are similar. But the @acronym{GNU} development tools can be configured as cross tools in almost any host+target permutation. All of these configurations can be installed concurrently. They can even be configured to share host independent files across hosts. Imake doesn't address these issues. Imake templates are a form of standardization. The @acronym{GNU} coding standards address the same issues without necessarily imposing the same restrictions. @end quotation Here is some further explanation, written by Per Bothner: @quotation One of the advantages of Imake is that it easy to generate large makefiles using the @samp{#include} and macro mechanisms of @command{cpp}. However, @code{cpp} is not programmable: it has limited conditional facilities, and no looping. And @code{cpp} cannot inspect its environment. All of these problems are solved by using @code{sh} instead of @code{cpp}. The shell is fully programmable, has macro substitution, can execute (or source) other shell scripts, and can inspect its environment. @end quotation Paul Eggert elaborates more: @quotation With Autoconf, installers need not assume that Imake itself is already installed and working well. This may not seem like much of an advantage to people who are accustomed to Imake. But on many hosts Imake is not installed or the default installation is not working well, and requiring Imake to install a package hinders the acceptance of that package on those hosts. For example, the Imake template and configuration files might not be installed properly on a host, or the Imake build procedure might wrongly assume that all source files are in one big directory tree, or the Imake configuration might assume one compiler whereas the package or the installer needs to use another, or there might be a version mismatch between the Imake expected by the package and the Imake supported by the host. These problems are much rarer with Autoconf, where each package comes with its own independent configuration processor. Also, Imake often suffers from unexpected interactions between @command{make} and the installer's C preprocessor. The fundamental problem here is that the C preprocessor was designed to preprocess C programs, not makefiles. This is much less of a problem with Autoconf, which uses the general-purpose preprocessor M4, and where the package's author (rather than the installer) does the preprocessing in a standard way. @end quotation Finally, Mark Eichin notes: @quotation Imake isn't all that extensible, either. In order to add new features to Imake, you need to provide your own project template, and duplicate most of the features of the existing one. This means that for a sophisticated project, using the vendor-provided Imake templates fails to provide any leverage---since they don't cover anything that your own project needs (unless it is an X11 program). On the other side, though: The one advantage that Imake has over @command{configure}: @file{Imakefile} files tend to be much shorter (likewise, less redundant) than @file{Makefile.in} files. There is a fix to this, however---at least for the Kerberos V5 tree, we've modified things to call in common @file{post.in} and @file{pre.in} makefile fragments for the entire tree. This means that a lot of common things don't have to be duplicated, even though they normally are in @command{configure} setups. @end quotation @node Defining Directories @section How Do I @code{#define} Installation Directories? @display My program needs library files, installed in @code{datadir} and similar. If I use @example AC_DEFINE_UNQUOTED([DATADIR], [$datadir], [Define to the read-only architecture-independent data directory.]) @end example @noindent I get @example #define DATADIR "$@{prefix@}/share" @end example @end display As already explained, this behavior is on purpose, mandated by the @acronym{GNU} Coding Standards, see @ref{Installation Directory Variables}. There are several means to achieve a similar goal: @itemize @minus @item Do not use @code{AC_DEFINE} but use your makefile to pass the actual value of @code{datadir} via compilation flags. @xref{Installation Directory Variables}, for the details. @item This solution can be simplified when compiling a program: you may either extend the @code{CPPFLAGS}: @example CPPFLAGS = -DDATADIR='"$(datadir)"' @@CPPFLAGS@@ @end example @noindent or create a dedicated header file: @example DISTCLEANFILES = datadir.h datadir.h: Makefile echo '#define DATADIR "$(datadir)"' >$@@ @end example @item Use @code{AC_DEFINE} but have @command{configure} compute the literal value of @code{datadir} and others. Many people have wrapped macros to automate this task. For instance, the macro @code{AC_DEFINE_DIR} from the @uref{http://autoconf-archive.cryp.to/, Autoconf Macro Archive}. This solution does not conform to the @acronym{GNU} Coding Standards. @item Note that all the previous solutions hard wire the absolute name of these directories in the executables, which is not a good property. You may try to compute the names relative to @code{prefix}, and try to find @code{prefix} at runtime, this way your package is relocatable. Some macros are already available to address this issue: see @code{adl_COMPUTE_RELATIVE_PATHS} and @code{adl_COMPUTE_STANDARD_RELATIVE_PATHS} on the @uref{http://autoconf-archive.cryp.to/, Autoconf Macro Archive}. @end itemize @node autom4te.cache @section What is @file{autom4te.cache}? @display What is this directory @file{autom4te.cache}? Can I safely remove it? @end display In the @acronym{GNU} Build System, @file{configure.ac} plays a central role and is read by many tools: @command{autoconf} to create @file{configure}, @command{autoheader} to create @file{config.h.in}, @command{automake} to create @file{Makefile.in}, @command{autoscan} to check the completeness of @file{configure.ac}, @command{autoreconf} to check the @acronym{GNU} Build System components that are used. To ``read @file{configure.ac}'' actually means to compile it with M4, which can be a long process for complex @file{configure.ac}. This is why all these tools, instead of running directly M4, invoke @command{autom4te} (@pxref{autom4te Invocation}) which, while answering to a specific demand, stores additional information in @file{autom4te.cache} for future runs. For instance, if you run @command{autoconf}, behind the scenes, @command{autom4te} also stores information for the other tools, so that when you invoke @command{autoheader} or @command{automake} etc., reprocessing @file{configure.ac} is not needed. The speed up is frequently of 30%, and is increasing with the size of @file{configure.ac}. But it is and remains being simply a cache: you can safely remove it. @sp 1 @display Can I permanently get rid of it? @end display The creation of this cache can be disabled from @file{~/.autom4te.cfg}, see @ref{Customizing autom4te}, for more details. You should be aware that disabling the cache slows down the Autoconf test suite by 40%. The more @acronym{GNU} Build System components are used, the more the cache is useful; for instance running @samp{autoreconf -f} on the Core Utilities is twice slower without the cache @emph{although @option{--force} implies that the cache is not fully exploited}, and eight times slower than without @option{--force}. @node Present But Cannot Be Compiled @section Header Present But Cannot Be Compiled The most important guideline to bear in mind when checking for features is to mimic as much as possible the intended use. Unfortunately, old versions of @code{AC_CHECK_HEADER} and @code{AC_CHECK_HEADERS} failed to follow this idea, and called the preprocessor, instead of the compiler, to check for headers. As a result, incompatibilities between headers went unnoticed during configuration, and maintainers finally had to deal with this issue elsewhere. As of Autoconf 2.56 both checks are performed, and @code{configure} complains loudly if the compiler and the preprocessor do not agree. For the time being the result used is that of the preprocessor, to give maintainers time to adjust their @file{configure.ac}, but in the future, only the compiler will be considered. Consider the following example: @smallexample $ @kbd{cat number.h} typedef int number; $ @kbd{cat pi.h} const number pi = 3; $ @kbd{cat configure.ac} AC_INIT([Example], [1.0], [bug-example@@example.org]) AC_CHECK_HEADERS([pi.h]) $ @kbd{autoconf -Wall} $ @kbd{./configure} checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ISO C89... none needed checking how to run the C preprocessor... gcc -E checking for grep that handles long lines and -e... grep checking for egrep... grep -E checking for ANSI C header files... yes checking for sys/types.h... yes checking for sys/stat.h... yes checking for stdlib.h... yes checking for string.h... yes checking for memory.h... yes checking for strings.h... yes checking for inttypes.h... yes checking for stdint.h... yes checking for unistd.h... yes checking pi.h usability... no checking pi.h presence... yes configure: WARNING: pi.h: present but cannot be compiled configure: WARNING: pi.h: check for missing prerequisite headers? configure: WARNING: pi.h: see the Autoconf documentation configure: WARNING: pi.h: section "Present But Cannot Be Compiled" configure: WARNING: pi.h: proceeding with the preprocessor's result configure: WARNING: pi.h: in the future, the compiler will take precedence configure: WARNING: ## -------------------------------------- ## configure: WARNING: ## Report this to bug-example@@example.org ## configure: WARNING: ## -------------------------------------- ## checking for pi.h... yes @end smallexample @noindent The proper way the handle this case is using the fourth argument (@pxref{Generic Headers}): @example $ @kbd{cat configure.ac} AC_INIT([Example], [1.0], [bug-example@@example.org]) AC_CHECK_HEADERS([number.h pi.h], [], [], [[#ifdef HAVE_NUMBER_H # include #endif ]]) $ @kbd{autoconf -Wall} $ @kbd{./configure} checking for gcc... gcc checking for C compiler default output... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ANSI C... none needed checking for number.h... yes checking for pi.h... yes @end example See @ref{Particular Headers}, for a list of headers with their prerequisite. @c ===================================================== History of Autoconf. @node History @chapter History of Autoconf @cindex History of autoconf You may be wondering, Why was Autoconf originally written? How did it get into its present form? (Why does it look like gorilla spit?) If you're not wondering, then this chapter contains no information useful to you, and you might as well skip it. If you @emph{are} wondering, then let there be light@enddots{} @menu * Genesis:: Prehistory and naming of @command{configure} * Exodus:: The plagues of M4 and Perl * Leviticus:: The priestly code of portability arrives * Numbers:: Growth and contributors * Deuteronomy:: Approaching the promises of easy configuration @end menu @node Genesis @section Genesis In June 1991 I was maintaining many of the @acronym{GNU} utilities for the Free Software Foundation. As they were ported to more platforms and more programs were added, the number of @option{-D} options that users had to select in the makefile (around 20) became burdensome. Especially for me---I had to test each new release on a bunch of different systems. So I wrote a little shell script to guess some of the correct settings for the fileutils package, and released it as part of fileutils 2.0. That @command{configure} script worked well enough that the next month I adapted it (by hand) to create similar @command{configure} scripts for several other @acronym{GNU} utilities packages. Brian Berliner also adapted one of my scripts for his @acronym{CVS} revision control system. Later that summer, I learned that Richard Stallman and Richard Pixley were developing similar scripts to use in the @acronym{GNU} compiler tools; so I adapted my @command{configure} scripts to support their evolving interface: using the file name @file{Makefile.in} as the templates; adding @samp{+srcdir}, the first option (of many); and creating @file{config.status} files. @node Exodus @section Exodus As I got feedback from users, I incorporated many improvements, using Emacs to search and replace, cut and paste, similar changes in each of the scripts. As I adapted more @acronym{GNU} utilities packages to use @command{configure} scripts, updating them all by hand became impractical. Rich Murphey, the maintainer of the @acronym{GNU} graphics utilities, sent me mail saying that the @command{configure} scripts were great, and asking if I had a tool for generating them that I could send him. No, I thought, but I should! So I started to work out how to generate them. And the journey from the slavery of hand-written @command{configure} scripts to the abundance and ease of Autoconf began. Cygnus @command{configure}, which was being developed at around that time, is table driven; it is meant to deal mainly with a discrete number of system types with a small number of mainly unguessable features (such as details of the object file format). The automatic configuration system that Brian Fox had developed for Bash takes a similar approach. For general use, it seems to me a hopeless cause to try to maintain an up-to-date database of which features each variant of each operating system has. It's easier and more reliable to check for most features on the fly---especially on hybrid systems that people have hacked on locally or that have patches from vendors installed. I considered using an architecture similar to that of Cygnus @command{configure}, where there is a single @command{configure} script that reads pieces of @file{configure.in} when run. But I didn't want to have to distribute all of the feature tests with every package, so I settled on having a different @command{configure} made from each @file{configure.in} by a preprocessor. That approach also offered more control and flexibility. I looked briefly into using the Metaconfig package, by Larry Wall, Harlan Stenn, and Raphael Manfredi, but I decided not to for several reasons. The @command{Configure} scripts it produces are interactive, which I find quite inconvenient; I didn't like the ways it checked for some features (such as library functions); I didn't know that it was still being maintained, and the @command{Configure} scripts I had seen didn't work on many modern systems (such as System V R4 and NeXT); it wasn't flexible in what it could do in response to a feature's presence or absence; I found it confusing to learn; and it was too big and complex for my needs (I didn't realize then how much Autoconf would eventually have to grow). I considered using Perl to generate my style of @command{configure} scripts, but decided that M4 was better suited to the job of simple textual substitutions: it gets in the way less, because output is implicit. Plus, everyone already has it. (Initially I didn't rely on the @acronym{GNU} extensions to M4.) Also, some of my friends at the University of Maryland had recently been putting M4 front ends on several programs, including @code{tvtwm}, and I was interested in trying out a new language. @node Leviticus @section Leviticus Since my @command{configure} scripts determine the system's capabilities automatically, with no interactive user intervention, I decided to call the program that generates them Autoconfig. But with a version number tacked on, that name would be too long for old Unix file systems, so I shortened it to Autoconf. In the fall of 1991 I called together a group of fellow questers after the Holy Grail of portability (er, that is, alpha testers) to give me feedback as I encapsulated pieces of my handwritten scripts in M4 macros and continued to add features and improve the techniques used in the checks. Prominent among the testers were Fran@,{c}ois Pinard, who came up with the idea of making an Autoconf shell script to run M4 and check for unresolved macro calls; Richard Pixley, who suggested running the compiler instead of searching the file system to find include files and symbols, for more accurate results; Karl Berry, who got Autoconf to configure @TeX{} and added the macro index to the documentation; and Ian Lance Taylor, who added support for creating a C header file as an alternative to putting @option{-D} options in a makefile, so he could use Autoconf for his @acronym{UUCP} package. The alpha testers cheerfully adjusted their files again and again as the names and calling conventions of the Autoconf macros changed from release to release. They all contributed many specific checks, great ideas, and bug fixes. @node Numbers @section Numbers In July 1992, after months of alpha testing, I released Autoconf 1.0, and converted many @acronym{GNU} packages to use it. I was surprised by how positive the reaction to it was. More people started using it than I could keep track of, including people working on software that wasn't part of the @acronym{GNU} Project (such as TCL, FSP, and Kerberos V5). Autoconf continued to improve rapidly, as many people using the @command{configure} scripts reported problems they encountered. Autoconf turned out to be a good torture test for M4 implementations. Unix M4 started to dump core because of the length of the macros that Autoconf defined, and several bugs showed up in @acronym{GNU} M4 as well. Eventually, we realized that we needed to use some features that only @acronym{GNU} M4 has. 4.3@acronym{BSD} M4, in particular, has an impoverished set of builtin macros; the System V version is better, but still doesn't provide everything we need. More development occurred as people put Autoconf under more stresses (and to uses I hadn't anticipated). Karl Berry added checks for X11. david zuhn contributed C++ support. Fran@,{c}ois Pinard made it diagnose invalid arguments. Jim Blandy bravely coerced it into configuring @acronym{GNU} Emacs, laying the groundwork for several later improvements. Roland McGrath got it to configure the @acronym{GNU} C Library, wrote the @command{autoheader} script to automate the creation of C header file templates, and added a @option{--verbose} option to @command{configure}. Noah Friedman added the @option{--autoconf-dir} option and @code{AC_MACRODIR} environment variable. (He also coined the term @dfn{autoconfiscate} to mean ``adapt a software package to use Autoconf''.) Roland and Noah improved the quoting protection in @code{AC_DEFINE} and fixed many bugs, especially when I got sick of dealing with portability problems from February through June, 1993. @node Deuteronomy @section Deuteronomy A long wish list for major features had accumulated, and the effect of several years of patching by various people had left some residual cruft. In April 1994, while working for Cygnus Support, I began a major revision of Autoconf. I added most of the features of the Cygnus @command{configure} that Autoconf had lacked, largely by adapting the relevant parts of Cygnus @command{configure} with the help of david zuhn and Ken Raeburn. These features include support for using @file{config.sub}, @file{config.guess}, @option{--host}, and @option{--target}; making links to files; and running @command{configure} scripts in subdirectories. Adding these features enabled Ken to convert @acronym{GNU} @code{as}, and Rob Savoye to convert Deja@acronym{GNU}, to using Autoconf. I added more features in response to other peoples' requests. Many people had asked for @command{configure} scripts to share the results of the checks between runs, because (particularly when configuring a large source tree, like Cygnus does) they were frustratingly slow. Mike Haertel suggested adding site-specific initialization scripts. People distributing software that had to unpack on MS-DOS asked for a way to override the @file{.in} extension on the file names, which produced file names like @file{config.h.in} containing two dots. Jim Avera did an extensive examination of the problems with quoting in @code{AC_DEFINE} and @code{AC_SUBST}; his insights led to significant improvements. Richard Stallman asked that compiler output be sent to @file{config.log} instead of @file{/dev/null}, to help people debug the Emacs @command{configure} script. I made some other changes because of my dissatisfaction with the quality of the program. I made the messages showing results of the checks less ambiguous, always printing a result. I regularized the names of the macros and cleaned up coding style inconsistencies. I added some auxiliary utilities that I had developed to help convert source code packages to use Autoconf. With the help of Fran@,{c}ois Pinard, I made the macros not interrupt each others' messages. (That feature revealed some performance bottlenecks in @acronym{GNU} M4, which he hastily corrected!) I reorganized the documentation around problems people want to solve. And I began a test suite, because experience had shown that Autoconf has a pronounced tendency to regress when we change it. Again, several alpha testers gave invaluable feedback, especially Fran@,{c}ois Pinard, Jim Meyering, Karl Berry, Rob Savoye, Ken Raeburn, and Mark Eichin. Finally, version 2.0 was ready. And there was much rejoicing. (And I have free time again. I think. Yeah, right.) @c ========================================================== Appendices @node Copying This Manual @appendix Copying This Manual @cindex License @menu * GNU Free Documentation License:: License for copying this manual @end menu @include fdl.texi @node Indices @appendix Indices @menu * Environment Variable Index:: Index of environment variables used * Output Variable Index:: Index of variables set in output files * Preprocessor Symbol Index:: Index of C preprocessor symbols defined * Autoconf Macro Index:: Index of Autoconf macros * M4 Macro Index:: Index of M4, M4sugar, and M4sh macros * Autotest Macro Index:: Index of Autotest macros * Program & Function Index:: Index of those with portability problems * Concept Index:: General index @end menu @node Environment Variable Index @appendixsec Environment Variable Index This is an alphabetical list of the environment variables that Autoconf checks. @printindex ev @node Output Variable Index @appendixsec Output Variable Index This is an alphabetical list of the variables that Autoconf can substitute into files that it creates, typically one or more makefiles. @xref{Setting Output Variables}, for more information on how this is done. @printindex ov @node Preprocessor Symbol Index @appendixsec Preprocessor Symbol Index This is an alphabetical list of the C preprocessor symbols that the Autoconf macros define. To work with Autoconf, C source code needs to use these names in @code{#if} or @code{#ifdef} directives. @printindex cv @node Autoconf Macro Index @appendixsec Autoconf Macro Index This is an alphabetical list of the Autoconf macros. @ifset shortindexflag To make the list easier to use, the macros are listed without their preceding @samp{AC_}. @end ifset @printindex AC @node M4 Macro Index @appendixsec M4 Macro Index This is an alphabetical list of the M4, M4sugar, and M4sh macros. @ifset shortindexflag To make the list easier to use, the macros are listed without their preceding @samp{m4_} or @samp{AS_}. @end ifset @printindex MS @node Autotest Macro Index @appendixsec Autotest Macro Index This is an alphabetical list of the Autotest macros. @ifset shortindexflag To make the list easier to use, the macros are listed without their preceding @samp{AT_}. @end ifset @printindex AT @node Program & Function Index @appendixsec Program and Function Index This is an alphabetical list of the programs and functions which portability is discussed in this document. @printindex pr @node Concept Index @appendixsec Concept Index This is an alphabetical list of the files, tools, and concepts introduced in this document. @printindex cp @bye @c LocalWords: texinfo setfilename autoconf texi settitle setchapternewpage @c LocalWords: setcontentsaftertitlepage finalout ARG ovar varname dvar acx @c LocalWords: makeinfo dvi defcodeindex ev ov CPP cv Autotest mv defindex fn @c LocalWords: shortindexflag iftex ifset acindex ACindex ifclear ahindex fu @c LocalWords: asindex MSindex atindex ATindex auindex hdrindex prindex FIXME @c LocalWords: msindex alloca fnindex Aaarg indices FSF's dircategory ifnames @c LocalWords: direntry autoscan autoreconf autoheader autoupdate config FDs @c LocalWords: testsuite titlepage Elliston Demaille vskip filll ifnottex hmm @c LocalWords: insertcopying Autoconf's detailmenu Automake Libtool Posix ois @c LocalWords: Systemology Checkpointing Changequote INTERCAL changequote dfn @c LocalWords: Quadrigraphs builtins Shellology acconfig Bugward LIBOBJ Imake @c LocalWords: LIBOBJS IFELSE cindex flushright Pinard Metaconfig uref Simons @c LocalWords: distclean uninstall noindent versioning Tromey dir @c LocalWords: SAMS samp aclocal acsite underquoted emph itemx prepend SUBST @c LocalWords: evindex automake Gettext autopoint gettext symlink libtoolize @c LocalWords: defmac INIT tarname ovindex cvindex BUGREPORT PREREQ asis PROG @c LocalWords: SRCDIR srcdir globbing afterwards cmds foos fooo foooo init cd @c LocalWords: builddir timestamp src Imakefile chmod defvar CFLAGS CPPFLAGS @c LocalWords: CXXFLAGS DEFS DHAVE defvarx FCFLAGS FFLAGS LDFLAGS bindir GCC @c LocalWords: datadir datarootdir docdir dvidir htmldir libdir ifnothtml kbd @c LocalWords: includedir infodir libexecdir localedir localstatedir mandir @c LocalWords: oldincludedir pdfdir PDF psdir PostScript sbindir sysconfdir @c LocalWords: sharedstatedir DDATADIR sed tmp pkgdatadir VPATH conf unistd @c LocalWords: undef endif builtin FUNCS ifndef STACKSEG getb GETB YMP fubar @c LocalWords: PRE dest SUBDIRS subdirs fi struct STDC stdlib stddef INTTYPES @c LocalWords: inttypes STDINT stdint AWK AIX Solaris NeXT env EGREP FGREP yy @c LocalWords: LEXLIB YYTEXT lfl nonportable Automake's LN RANLIB byacc INETD @c LocalWords: inetd prog PROGS progs ranlib lmp lXt lX nsl gethostbyname UX @c LocalWords: NextStep isinf isnan glibc IRIX sunmath lm lsunmath pre sizeof @c LocalWords: ld inline malloc putenv setenv FreeBSD realloc SunOS MinGW @c LocalWords: snprintf vsnprintf sprintf vsprintf sscanf gcc strerror ifdef @c LocalWords: strnlen sysconf PAGESIZE unsetenv va fallback memcpy dst FUNC @c LocalWords: PowerPC GNUC libPW pragma Olibcalls CHOWN chown CLOSEDIR VFORK @c LocalWords: closedir FNMATCH fnmatch vfork FSEEKO LARGEFILE fseeko SVR sc @c LocalWords: largefile GETGROUPS getgroups GETLOADAVG DGUX UMAX NLIST KMEM @c LocalWords: GETLODAVG SETGID getloadavg nlist GETMNTENT irix @c LocalWords: getmntent UnixWare GETPGRP getpgid getpgrp Posix's pid LSTAT @c LocalWords: lstat rpl MEMCMP memcmp OpenStep MBRTOWC mbrtowc MKTIME mktime @c LocalWords: localtime MMAP mmap OBSTACK obstack obstacks ARGTYPES timeval @c LocalWords: SETPGRP setpgrp defmacx Hurd SETVBUF setvbuf STRCOLL strcoll @c LocalWords: STRTOD strtod DECL STRFTIME strftime SCO UTIME utime VPRINTF @c LocalWords: DOPRNT vprintf doprnt sp unfixable LIBSOURCE LIBSOURCES Eggert @c LocalWords: linux netinet ia Tru XFree DIRENT NDIR dirent ndir multitable @c LocalWords: NAMLEN strlen namlen MKDEV SYSMACROS makedev RESOLV resolv DNS @c LocalWords: inet structs NAMESER arpa NETDB netdb UTekV UTS autom GCC's kB @c LocalWords: STDBOOL BOOL stdbool conformant cplusplus bool Bool stdarg tm @c LocalWords: ctype strchr strrchr rindex bcopy memmove memchr WEXITSTATUS @c LocalWords: WIFEXITED TIOCGWINSZ GWINSZ termios preprocess preprocessable @c LocalWords: DECLS strdup calloc BLKSIZE blksize RDEV rdev TZNAME tzname pw @c LocalWords: passwd gecos pwd MBSTATE mbstate wchar RETSIGTYPE hup UID uid @c LocalWords: gid ptrdiff uintmax EXEEXT OBJEXT Ae Onolimit conftest AXP str @c LocalWords: ALIGNOF WERROR Werror cpp HP's WorkShop egcs un fied stdc CXX @c LocalWords: varargs BIGENDIAN Endianness SPARC endianness grep'ed CONST FC @c LocalWords: const STRINGIZE stringizing PARAMS unprotoize protos KCC cxx @c LocalWords: xlC aCC CXXCPP FREEFORM xlf FLIBS FCLIBS ish SRCEXT XTRA LFS @c LocalWords: ISC lcposix MINIX Minix conditionalized inlines hw dD confdefs @c LocalWords: fputs stdout PREPROC ar UFS HFS QNX realtime fstype STATVFS se @c LocalWords: statvfs STATFS statfs func machfile hdr lelf raboof DEFUN GTK @c LocalWords: GTKMM Grmph ified ine defn baz EOF qar Ahhh changecom algol io @c LocalWords: changeword quadrigraphs quadrigraph dnl SGI atoi overquoting @c LocalWords: Aas Wcross sep args namespace undefine bpatsubst popdef dquote @c LocalWords: bregexp Overquote overquotation meisch maisch meische maische @c LocalWords: miscian DIRNAME dirname MKDIR CATFILE XMKMF TRAVOLTA celsius @c LocalWords: EMX emxos Emacsen Korn DYNIX subshell posix Ksh ksh Pdksh Zsh @c LocalWords: pdksh zsh Allbery Lipe Kubota UWS zorglub stderr eval esac lfn @c LocalWords: drivespec Posixy DJGPP doschk prettybird LPT pfew Zsh's yu yaa @c LocalWords: yM uM aM firebird IP subdir misparses ok Unpatched abc bc zA @c LocalWords: CDPATH DUALCASE LINENO prepass Subshells lineno NULLCMD cmp wc @c LocalWords: MAILPATH scanset arg NetBSD Almquist printf expr cp @c LocalWords: Oliva awk Aaaaarg cmd regex xfoo GNV OpenVMS VM @c LocalWords: sparc Proulx SysV nbar nfoo maxdepth acdilrtu TWG mc @c LocalWords: mkdir exe uname OpenBSD Fileutils mktemp umask TMPDIR guid os @c LocalWords: fooXXXXXX Unicos parenthesization utimes hpux hppa unescaped @c LocalWords: pmake DOS's gmake ifoo DESTDIR autoconfiscated pc coff mips gg @c LocalWords: dec ultrix cpu wildcards rpcc rdtsc powerpc readline @c LocalWords: withval vxworks gless localcache usr LOFF loff CYGWIN Cygwin @c LocalWords: cygwin SIGLIST siglist SYSNDIR SYSDIR ptx lseq rusage elif MSC @c LocalWords: lfoo POUNDBANG lsun NIS getpwnam SYSCALLS RSH INTL lintl aix @c LocalWords: intl lx ldir syslog bsd EPI toolchain netbsd objext de KNR nn @c LocalWords: fication LTLIBOBJS Wdiff TESTDIR atconfig atlocal akim XFAIL @c LocalWords: ChangeLog prepended errexit smallexample TESTSUITEFLAGS GPL er @c LocalWords: installcheck autotest indir Pixley Bothner Eichin Kerberos adl @c LocalWords: DISTCLEANFILES preprocessor's fileutils Stallman Murphey Stenn @c LocalWords: Manfredi Autoconfig TCL FSP david zuhn Blandy MACRODIR Raeburn @c LocalWords: autoconfiscate Savoye Haertel Avera Meyering fdl appendixsec @c LocalWords: printindex american LIBOBJDIR LibdirTest ERLCFLAGS OBJCFLAGS @c LocalWords: VER Gnulib online xyes strcpy TYPEOF typeof OBJC objcc objc ln @c LocalWords: GOBJC OBJCCPP OTP ERLC erl valloc decr dumpdef errprint incr @c LocalWords: esyscmd len maketemp pushdef substr syscmd sysval translit txt @c LocalWords: sinclude foreach myvar tolower toupper uniq BASENAME STDIN @c LocalWords: Dynix descrips basename aname cname macroexpands xno xcheck @c LocalWords: LIBREADLINE lreadline lncurses libreadline @c Local Variables: @c fill-column: 72 @c ispell-local-dictionary: "american" @c indent-tabs-mode: nil @c whitespace-check-buffer-indent: nil @c End: