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172 lines
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Plaintext
172 lines
7.2 KiB
Plaintext
@c This is part of the Emacs manual.
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@c Copyright (C) 1985, 86, 87, 93, 94, 95, 97, 2000 Free Software Foundation, Inc.
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@c See file emacs.texi for copying conditions.
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@node Major Modes, Indentation, International, Top
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@chapter Major Modes
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@cindex major modes
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@cindex mode, major
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@kindex TAB @r{(and major modes)}
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@kindex DEL @r{(and major modes)}
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@kindex C-j @r{(and major modes)}
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Emacs provides many alternative @dfn{major modes}, each of which
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customizes Emacs for editing text of a particular sort. The major modes
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are mutually exclusive, and each buffer has one major mode at any time.
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The mode line normally shows the name of the current major mode, in
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parentheses (@pxref{Mode Line}).
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The least specialized major mode is called @dfn{Fundamental mode}.
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This mode has no mode-specific redefinitions or variable settings, so
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that each Emacs command behaves in its most general manner, and each
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option is in its default state. For editing text of a specific type
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that Emacs knows about, such as Lisp code or English text, you should
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switch to the appropriate major mode, such as Lisp mode or Text mode.
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Selecting a major mode changes the meanings of a few keys to become
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more specifically adapted to the language being edited. The ones that
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are changed frequently are @key{TAB}, @key{DEL}, and @kbd{C-j}. The
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prefix key @kbd{C-c} normally contains mode-specific commands. In
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addition, the commands which handle comments use the mode to determine
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how comments are to be delimited. Many major modes redefine the
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syntactical properties of characters appearing in the buffer.
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@xref{Syntax}.
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The major modes fall into three major groups. The first group
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contains modes for normal text, either plain or with mark-up. It
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includes Text mode, HTML mode, SGML mode, @TeX{} mode and Outline
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mode. The second group contains modes for specific programming
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languages. These include Lisp mode (which has several variants), C
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mode, Fortran mode, and others. The remaining major modes are not
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intended for use on users' files; they are used in buffers created for
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specific purposes by Emacs, such as Dired mode for buffers made by
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Dired (@pxref{Dired}), Mail mode for buffers made by @kbd{C-x m}
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(@pxref{Sending Mail}), and Shell mode for buffers used for
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communicating with an inferior shell process (@pxref{Interactive
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Shell}).
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Most programming-language major modes specify that only blank lines
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separate paragraphs. This is to make the paragraph commands useful.
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(@xref{Paragraphs}.) They also cause Auto Fill mode to use the
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definition of @key{TAB} to indent the new lines it creates. This is
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because most lines in a program are usually indented
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(@pxref{Indentation}).
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@menu
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* Choosing Modes:: How major modes are specified or chosen.
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@end menu
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@node Choosing Modes,,Major Modes,Major Modes
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@section How Major Modes are Chosen
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@cindex choosing a major mode
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You can select a major mode explicitly for the current buffer, but
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most of the time Emacs determines which mode to use based on the file
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name or on special text in the file.
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Explicit selection of a new major mode is done with a @kbd{M-x} command.
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From the name of a major mode, add @code{-mode} to get the name of a
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command to select that mode. Thus, you can enter Lisp mode by executing
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@kbd{M-x lisp-mode}.
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@vindex auto-mode-alist
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When you visit a file, Emacs usually chooses the right major mode based
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on the file's name. For example, files whose names end in @samp{.c} are
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edited in C mode. The correspondence between file names and major modes is
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controlled by the variable @code{auto-mode-alist}. Its value is a list in
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which each element has this form,
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@example
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(@var{regexp} . @var{mode-function})
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@end example
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@noindent
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or this form,
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@example
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(@var{regexp} @var{mode-function} @var{flag})
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@end example
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@noindent
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For example, one element normally found in the list has the form
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@code{(@t{"\\.c\\'"} . c-mode)}, and it is responsible for selecting C
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mode for files whose names end in @file{.c}. (Note that @samp{\\} is
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needed in Lisp syntax to include a @samp{\} in the string, which must
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be used to suppress the special meaning of @samp{.} in regexps.) If the
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element has the form @code{(@var{regexp} @var{mode-function}
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@var{flag})} and @var{flag} is non-@code{nil}, then after calling
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@var{mode-function}, the suffix that matched @var{regexp} is discarded
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and the list is searched again for another match.
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You can specify which major mode should be used for editing a certain
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file by a special sort of text in the first nonblank line of the file. The
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mode name should appear in this line both preceded and followed by
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@samp{-*-}. Other text may appear on the line as well. For example,
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@example
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;-*-Lisp-*-
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@end example
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@noindent
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tells Emacs to use Lisp mode. Such an explicit specification overrides
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any defaults based on the file name. Note how the semicolon is used
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to make Lisp treat this line as a comment.
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Another format of mode specification is
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@example
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-*- mode: @var{modename};-*-
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@end example
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@noindent
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which allows you to specify local variables as well, like this:
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@example
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-*- mode: @var{modename}; @var{var}: @var{value}; @dots{} -*-
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@end example
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@noindent
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@xref{File Variables}, for more information about this.
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@vindex interpreter-mode-alist
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When a file's contents begin with @samp{#!}, it can serve as an
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executable shell command, which works by running an interpreter named on
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the file's first line. The rest of the file is used as input to the
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interpreter.
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When you visit such a file in Emacs, if the file's name does not
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specify a major mode, Emacs uses the interpreter name on the first line
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to choose a mode. If the first line is the name of a recognized
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interpreter program, such as @samp{perl} or @samp{tcl}, Emacs uses a
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mode appropriate for programs for that interpreter. The variable
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@code{interpreter-mode-alist} specifies the correspondence between
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interpreter program names and major modes.
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When the first line starts with @samp{#!}, you cannot (on many
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systems) use the @samp{-*-} feature on the first line, because the
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system would get confused when running the interpreter. So Emacs looks
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for @samp{-*-} on the second line in such files as well as on the
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first line.
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@vindex default-major-mode
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When you visit a file that does not specify a major mode to use, or
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when you create a new buffer with @kbd{C-x b}, the variable
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@code{default-major-mode} specifies which major mode to use. Normally
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its value is the symbol @code{fundamental-mode}, which specifies
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Fundamental mode. If @code{default-major-mode} is @code{nil}, the major
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mode is taken from the previously current buffer.
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@findex normal-mode
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If you change the major mode of a buffer, you can go back to the major
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mode Emacs would choose automatically: use the command @kbd{M-x
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normal-mode} to do this. This is the same function that
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@code{find-file} calls to choose the major mode. It also processes
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the file's local variables list (if any).
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@vindex change-major-mode-with-file-name
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The commands @kbd{C-x C-w} and @code{set-visited-file-name} change to
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a new major mode if the new file name implies a mode (@pxref{Saving}).
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However, this does not happen if the buffer contents specify a major
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mode, and certain ``special'' major modes do not allow the mode to
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change. You can turn off this mode-changing feature by setting
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@code{change-major-mode-with-file-name} to @code{nil}.
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