1@c This is part of the Emacs manual. 2@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2000, 2001, 3@c 2002, 2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc. 4@c See file emacs.texi for copying conditions. 5@node Major Modes, Indentation, International, Top 6@chapter Major Modes 7@cindex major modes 8@cindex mode, major 9@kindex TAB @r{(and major modes)} 10@kindex DEL @r{(and major modes)} 11@kindex C-j @r{(and major modes)} 12 13 Emacs provides many alternative @dfn{major modes}, each of which 14customizes Emacs for editing text of a particular sort. The major modes 15are mutually exclusive, and each buffer has one major mode at any time. 16The mode line normally shows the name of the current major mode, in 17parentheses (@pxref{Mode Line}). 18 19 The least specialized major mode is called @dfn{Fundamental mode}. 20This mode has no mode-specific redefinitions or variable settings, so 21that each Emacs command behaves in its most general manner, and each 22user option variable is in its default state. For editing text of a 23specific type that Emacs knows about, such as Lisp code or English 24text, you should switch to the appropriate major mode, such as Lisp 25mode or Text mode. 26 27 Selecting a major mode changes the meanings of a few keys to become 28more specifically adapted to the language being edited. The ones that 29are changed frequently are @key{TAB}, @key{DEL}, and @kbd{C-j}. The 30prefix key @kbd{C-c} normally contains mode-specific commands. In 31addition, the commands which handle comments use the mode to determine 32how comments are to be delimited. Many major modes redefine the 33syntactical properties of characters appearing in the buffer. 34@xref{Syntax}. 35 36 The major modes fall into three major groups. The first group 37contains modes for normal text, either plain or with mark-up. It 38includes Text mode, HTML mode, SGML mode, @TeX{} mode and Outline 39mode. The second group contains modes for specific programming 40languages. These include Lisp mode (which has several variants), C 41mode, Fortran mode, and others. The remaining major modes are not 42intended for use on users' files; they are used in buffers created for 43specific purposes by Emacs, such as Dired mode for buffers made by 44Dired (@pxref{Dired}), Mail mode for buffers made by @kbd{C-x m} 45(@pxref{Sending Mail}), and Shell mode for buffers used for 46communicating with an inferior shell process (@pxref{Interactive 47Shell}). 48 49 Most programming-language major modes specify that only blank lines 50separate paragraphs. This is to make the paragraph commands useful. 51(@xref{Paragraphs}.) They also cause Auto Fill mode to use the 52definition of @key{TAB} to indent the new lines it creates. This is 53because most lines in a program are usually indented 54(@pxref{Indentation}). 55 56@menu 57* Choosing Modes:: How major modes are specified or chosen. 58@end menu 59 60@node Choosing Modes,,Major Modes,Major Modes 61@section How Major Modes are Chosen 62 63@cindex choosing a major mode 64 You can select a major mode explicitly for the current buffer, but 65most of the time Emacs determines which mode to use based on the file 66name or on special text in the file. 67 68 To explicitly select a new major, you use an @kbd{M-x} command. 69Take the name of a major mode and add @code{-mode} to get the name of 70the command to select that mode. Thus, you can enter Lisp mode by 71executing @kbd{M-x lisp-mode}. 72 73@vindex auto-mode-alist 74 When you visit a file, Emacs usually chooses the right major mode based 75on the file's name. For example, files whose names end in @samp{.c} are 76edited in C mode. The correspondence between file names and major modes is 77controlled by the variable @code{auto-mode-alist}. Its value is a list in 78which each element has this form, 79 80@example 81(@var{regexp} . @var{mode-function}) 82@end example 83 84@noindent 85or this form, 86 87@example 88(@var{regexp} @var{mode-function} @var{flag}) 89@end example 90 91@noindent 92For example, one element normally found in the list has the form 93@code{(@t{"\\.c\\'"} . c-mode)}, and it is responsible for selecting C 94mode for files whose names end in @file{.c}. (Note that @samp{\\} is 95needed in Lisp syntax to include a @samp{\} in the string, which must 96be used to suppress the special meaning of @samp{.} in regexps.) If 97the element has the form @code{(@var{regexp} @var{mode-function} 98@var{flag})} and @var{flag} is non-@code{nil}, then after calling 99@var{mode-function}, Emacs discards the suffix that matched 100@var{regexp} and searches the list again for another match. 101 102@vindex magic-mode-alist 103 Sometimes the major mode is determined from the way the file's text 104begins. The variable @code{magic-mode-alist} controls this. Its value 105is a list of elements of these forms: 106 107@example 108(@var{regexp} . @var{mode-function}) 109(@var{match-function} . @var{mode-function}) 110@end example 111 112@noindent 113The first form looks like an element of @code{auto-mode-alist}, but it 114doesn't work the same: this @var{regexp} is matched against the text 115at the start of the buffer, not against the file name. Likewise, the 116second form calls @var{match-function} at the beginning of the buffer, 117and if the function returns non-@code{nil}, the @var{mode-function} is 118called. @code{magic-mode-alist} takes priority over 119@code{auto-mode-alist}. 120 121 You can specify the major mode to use for editing a certain file by 122special text in the first nonblank line of the file. The 123mode name should appear in this line both preceded and followed by 124@samp{-*-}. Other text may appear on the line as well. For example, 125 126@example 127;-*-Lisp-*- 128@end example 129 130@noindent 131tells Emacs to use Lisp mode. Such an explicit specification overrides 132any defaults based on the file name. Note how the semicolon is used 133to make Lisp treat this line as a comment. 134 135 Another format of mode specification is 136 137@example 138-*- mode: @var{modename};-*- 139@end example 140 141@noindent 142which allows you to specify local variables as well, like this: 143 144@example 145-*- mode: @var{modename}; @var{var}: @var{value}; @dots{} -*- 146@end example 147 148@noindent 149@xref{File Variables}, for more information about this. 150 151@vindex auto-mode-case-fold 152 On systems with case-insensitive file names, only a single 153case-insensitive search through the @code{auto-mode-alist} is made. 154On other systems, Emacs normally performs a single case-sensitive 155search through the alist, but if you set this variable to a 156non-@code{nil} value, Emacs will perform a second case-insensitive 157search if the first search fails. 158 159@vindex interpreter-mode-alist 160 When a file's contents begin with @samp{#!}, it can serve as an 161executable shell command, which works by running an interpreter named on 162the file's first line. The rest of the file is used as input to the 163interpreter. 164 165 When you visit such a file in Emacs, if the file's name does not 166specify a major mode, Emacs uses the interpreter name on the first line 167to choose a mode. If the first line is the name of a recognized 168interpreter program, such as @samp{perl} or @samp{tcl}, Emacs uses a 169mode appropriate for programs for that interpreter. The variable 170@code{interpreter-mode-alist} specifies the correspondence between 171interpreter program names and major modes. 172 173 When the first line starts with @samp{#!}, you cannot (on many 174systems) use the @samp{-*-} feature on the first line, because the 175system would get confused when running the interpreter. So Emacs looks 176for @samp{-*-} on the second line in such files as well as on the 177first line. 178 179@vindex default-major-mode 180 When you visit a file that does not specify a major mode to use, or 181when you create a new buffer with @kbd{C-x b}, the variable 182@code{default-major-mode} specifies which major mode to use. Normally 183its value is the symbol @code{fundamental-mode}, which specifies 184Fundamental mode. If @code{default-major-mode} is @code{nil}, the major 185mode is taken from the previously current buffer. 186 187@findex normal-mode 188 If you change the major mode of a buffer, you can go back to the major 189mode Emacs would choose automatically: use the command @kbd{M-x 190normal-mode} to do this. This is the same function that 191@code{find-file} calls to choose the major mode. It also processes 192the file's @samp{-*-} line or local variables list (if any). 193@xref{File Variables}. 194 195@vindex change-major-mode-with-file-name 196 The commands @kbd{C-x C-w} and @code{set-visited-file-name} change to 197a new major mode if the new file name implies a mode (@pxref{Saving}). 198(@kbd{C-x C-s} does this too, if the buffer wasn't visiting a file.) 199However, this does not happen if the buffer contents specify a major 200mode, and certain ``special'' major modes do not allow the mode to 201change. You can turn off this mode-changing feature by setting 202@code{change-major-mode-with-file-name} to @code{nil}. 203 204@ignore 205 arch-tag: f2558800-cf32-4839-8acb-7d3b4df2a155 206@end ignore 207