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