1<html> 2<head> 3<title>pcreposix specification</title> 4</head> 5<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6<h1>pcreposix man page</h1> 7<p> 8Return to the <a href="index.html">PCRE index page</a>. 9</p> 10<p> 11This page is part of the PCRE HTML documentation. It was generated automatically 12from the original man page. If there is any nonsense in it, please consult the 13man page, in case the conversion went wrong. 14<br> 15<ul> 16<li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a> 17<li><a name="TOC2" href="#SEC2">DESCRIPTION</a> 18<li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a> 19<li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a> 20<li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a> 21<li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a> 22<li><a name="TOC7" href="#SEC7">MEMORY USAGE</a> 23<li><a name="TOC8" href="#SEC8">AUTHOR</a> 24<li><a name="TOC9" href="#SEC9">REVISION</a> 25</ul> 26<br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br> 27<P> 28<b>#include <pcreposix.h></b> 29</P> 30<P> 31<b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b> 32<b>int <i>cflags</i>);</b> 33</P> 34<P> 35<b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b> 36<b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b> 37</P> 38<P> 39<b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b> 40<b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b> 41</P> 42<P> 43<b>void regfree(regex_t *<i>preg</i>);</b> 44</P> 45<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> 46<P> 47This set of functions provides a POSIX-style API to the PCRE regular expression 48package. See the 49<a href="pcreapi.html"><b>pcreapi</b></a> 50documentation for a description of PCRE's native API, which contains much 51additional functionality. 52</P> 53<P> 54The functions described here are just wrapper functions that ultimately call 55the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b> 56header file, and on Unix systems the library itself is called 57<b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the 58command for linking an application that uses them. Because the POSIX functions 59call the native ones, it is also necessary to add <b>-lpcre</b>. 60</P> 61<P> 62I have implemented only those POSIX option bits that can be reasonably mapped 63to PCRE native options. In addition, the option REG_EXTENDED is defined with 64the value zero. This has no effect, but since programs that are written to the 65POSIX interface often use it, this makes it easier to slot in PCRE as a 66replacement library. Other POSIX options are not even defined. 67</P> 68<P> 69There are also some other options that are not defined by POSIX. These have 70been added at the request of users who want to make use of certain 71PCRE-specific features via the POSIX calling interface. 72</P> 73<P> 74When PCRE is called via these functions, it is only the API that is POSIX-like 75in style. The syntax and semantics of the regular expressions themselves are 76still those of Perl, subject to the setting of various PCRE options, as 77described below. "POSIX-like in style" means that the API approximates to the 78POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding 79domains it is probably even less compatible. 80</P> 81<P> 82The header for these functions is supplied as <b>pcreposix.h</b> to avoid any 83potential clash with other POSIX libraries. It can, of course, be renamed or 84aliased as <b>regex.h</b>, which is the "correct" name. It provides two 85structure types, <i>regex_t</i> for compiled internal forms, and 86<i>regmatch_t</i> for returning captured substrings. It also defines some 87constants whose names start with "REG_"; these are used for setting options and 88identifying error codes. 89</P> 90<P> 91</P> 92<br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br> 93<P> 94The function <b>regcomp()</b> is called to compile a pattern into an 95internal form. The pattern is a C string terminated by a binary zero, and 96is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer 97to a <b>regex_t</b> structure that is used as a base for storing information 98about the compiled regular expression. 99</P> 100<P> 101The argument <i>cflags</i> is either zero, or contains one or more of the bits 102defined by the following macros: 103<pre> 104 REG_DOTALL 105</pre> 106The PCRE_DOTALL option is set when the regular expression is passed for 107compilation to the native function. Note that REG_DOTALL is not part of the 108POSIX standard. 109<pre> 110 REG_ICASE 111</pre> 112The PCRE_CASELESS option is set when the regular expression is passed for 113compilation to the native function. 114<pre> 115 REG_NEWLINE 116</pre> 117The PCRE_MULTILINE option is set when the regular expression is passed for 118compilation to the native function. Note that this does <i>not</i> mimic the 119defined POSIX behaviour for REG_NEWLINE (see the following section). 120<pre> 121 REG_NOSUB 122</pre> 123The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed 124for compilation to the native function. In addition, when a pattern that is 125compiled with this flag is passed to <b>regexec()</b> for matching, the 126<i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings 127are returned. 128<pre> 129 REG_UNGREEDY 130</pre> 131The PCRE_UNGREEDY option is set when the regular expression is passed for 132compilation to the native function. Note that REG_UNGREEDY is not part of the 133POSIX standard. 134<pre> 135 REG_UTF8 136</pre> 137The PCRE_UTF8 option is set when the regular expression is passed for 138compilation to the native function. This causes the pattern itself and all data 139strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8 140is not part of the POSIX standard. 141</P> 142<P> 143In the absence of these flags, no options are passed to the native function. 144This means the the regex is compiled with PCRE default semantics. In 145particular, the way it handles newline characters in the subject string is the 146Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only 147<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way 148newlines are matched by . (they are not) or by a negative class such as [^a] 149(they are). 150</P> 151<P> 152The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The 153<i>preg</i> structure is filled in on success, and one member of the structure 154is public: <i>re_nsub</i> contains the number of capturing subpatterns in 155the regular expression. Various error codes are defined in the header file. 156</P> 157<P> 158NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to 159use the contents of the <i>preg</i> structure. If, for example, you pass it to 160<b>regexec()</b>, the result is undefined and your program is likely to crash. 161</P> 162<br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br> 163<P> 164This area is not simple, because POSIX and Perl take different views of things. 165It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never 166intended to be a POSIX engine. The following table lists the different 167possibilities for matching newline characters in PCRE: 168<pre> 169 Default Change with 170 171 . matches newline no PCRE_DOTALL 172 newline matches [^a] yes not changeable 173 $ matches \n at end yes PCRE_DOLLARENDONLY 174 $ matches \n in middle no PCRE_MULTILINE 175 ^ matches \n in middle no PCRE_MULTILINE 176</pre> 177This is the equivalent table for POSIX: 178<pre> 179 Default Change with 180 181 . matches newline yes REG_NEWLINE 182 newline matches [^a] yes REG_NEWLINE 183 $ matches \n at end no REG_NEWLINE 184 $ matches \n in middle no REG_NEWLINE 185 ^ matches \n in middle no REG_NEWLINE 186</pre> 187PCRE's behaviour is the same as Perl's, except that there is no equivalent for 188PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop 189newline from matching [^a]. 190</P> 191<P> 192The default POSIX newline handling can be obtained by setting PCRE_DOTALL and 193PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the 194REG_NEWLINE action. 195</P> 196<br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br> 197<P> 198The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i> 199against a given <i>string</i>, which is by default terminated by a zero byte 200(but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can 201be: 202<pre> 203 REG_NOTBOL 204</pre> 205The PCRE_NOTBOL option is set when calling the underlying PCRE matching 206function. 207<pre> 208 REG_NOTEMPTY 209</pre> 210The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching 211function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, 212setting this option can give more POSIX-like behaviour in some situations. 213<pre> 214 REG_NOTEOL 215</pre> 216The PCRE_NOTEOL option is set when calling the underlying PCRE matching 217function. 218<pre> 219 REG_STARTEND 220</pre> 221The string is considered to start at <i>string</i> + <i>pmatch[0].rm_so</i> and 222to have a terminating NUL located at <i>string</i> + <i>pmatch[0].rm_eo</i> 223(there need not actually be a NUL at that location), regardless of the value of 224<i>nmatch</i>. This is a BSD extension, compatible with but not specified by 225IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software 226intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does 227not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not 228how it is matched. 229</P> 230<P> 231If the pattern was compiled with the REG_NOSUB flag, no data about any matched 232strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of 233<b>regexec()</b> are ignored. 234</P> 235<P> 236If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL, 237no data about any matched strings is returned. 238</P> 239<P> 240Otherwise,the portion of the string that was matched, and also any captured 241substrings, are returned via the <i>pmatch</i> argument, which points to an 242array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the 243members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first 244character of each substring and the offset to the first character after the end 245of each substring, respectively. The 0th element of the vector relates to the 246entire portion of <i>string</i> that was matched; subsequent elements relate to 247the capturing subpatterns of the regular expression. Unused entries in the 248array have both structure members set to -1. 249</P> 250<P> 251A successful match yields a zero return; various error codes are defined in the 252header file, of which REG_NOMATCH is the "expected" failure code. 253</P> 254<br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br> 255<P> 256The <b>regerror()</b> function maps a non-zero errorcode from either 257<b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not 258NULL, the error should have arisen from the use of that structure. A message 259terminated by a binary zero is placed in <i>errbuf</i>. The length of the 260message, including the zero, is limited to <i>errbuf_size</i>. The yield of the 261function is the size of buffer needed to hold the whole message. 262</P> 263<br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br> 264<P> 265Compiling a regular expression causes memory to be allocated and associated 266with the <i>preg</i> structure. The function <b>regfree()</b> frees all such 267memory, after which <i>preg</i> may no longer be used as a compiled expression. 268</P> 269<br><a name="SEC8" href="#TOC1">AUTHOR</a><br> 270<P> 271Philip Hazel 272<br> 273University Computing Service 274<br> 275Cambridge CB2 3QH, England. 276<br> 277</P> 278<br><a name="SEC9" href="#TOC1">REVISION</a><br> 279<P> 280Last updated: 02 September 2009 281<br> 282Copyright © 1997-2009 University of Cambridge. 283<br> 284<p> 285Return to the <a href="index.html">PCRE index page</a>. 286</p> 287