When Emacs visits a file, it automatically selects a major mode for the buffer based on information in the file name or in the file itself. It also processes local variables specified in the file text.
This function establishes the proper major mode and buffer-local variable
bindings for the current buffer. First it calls
(see below), then it runs
hack-local-variables to parse, and
bind or evaluate as appropriate, the file’s local variables
(see File Local Variables).
If the find-file argument to
normal-mode is non-
normal-mode assumes that the
find-file function is calling
it. In this case, it may process local variables in the ‘-*-’
line or at the end of the file. The variable
enable-local-variables controls whether to do so. See Local Variables in Files in The GNU Emacs Manual,
for the syntax of the local variables section of a file.
If you run
normal-mode interactively, the argument
find-file is normally
nil. In this case,
normal-mode unconditionally processes any file local variables.
The function calls
set-auto-mode to choose a major mode. If this
does not specify a mode, the buffer stays in the major mode determined
by the default value of major-mode (see below).
condition-case around the call to the
major mode command, so errors are caught and reported as a ‘File
mode specification error’, followed by the original error message.
This function selects the major mode that is appropriate for the
current buffer. It bases its decision (in order of precedence) on the
‘-*-’ line, on any ‘mode:’ local variable near the end of
a file, on the ‘#!’ line (using interpreter-mode-alist),
on the text at the beginning of the buffer (using
magic-mode-alist), and finally on the visited file name (using
auto-mode-alist). See How Major Modes are
Chosen in The GNU Emacs Manual. If enable-local-variables
set-auto-mode does not check the ‘-*-’
line, or near the end of the file, for any mode tag.
There are some file types where it is not appropriate to scan the file contents for a mode specifier. For example, a tar archive may happen to contain, near the end of the file, a member file that has a local variables section specifying a mode for that particular file. This should not be applied to the containing tar file. Similarly, a tiff image file might just happen to contain a first line that seems to match the ‘-*-’ pattern. For these reasons, both these file extensions are members of the list inhibit-local-variables-regexps. Add patterns to this list to prevent Emacs searching them for local variables of any kind (not just mode specifiers).
If keep-mode-if-same is non-
nil, this function does not
call the mode command if the buffer is already in the proper major
mode. For instance,
set-visited-file-name sets this to
t to avoid killing buffer local variables that the user may
This function sets the major mode of buffer to the default value of
major-mode; if that is
nil, it uses the
current buffer’s major mode (if that is suitable). As an exception,
if buffer’s name is *scratch*, it sets the mode to
The low-level primitives for creating buffers do not use this function,
but medium-level commands such as
find-file-noselect use it whenever they create buffers.
The value of this variable determines the major mode of the initial
*scratch* buffer. The value should be a symbol that is a major
mode command. The default value is
This variable specifies major modes to use for scripts that specify a
command interpreter in a ‘#!’ line. Its value is an alist with
elements of the form
(regexp . mode); this says to
use mode mode if the file specifies an interpreter which matches
\\`regexp\\'. For example, one of the default elements
("python[0-9.]*" . python-mode).
This variable’s value is an alist with elements of the form
(regexp . function), where regexp is a
regular expression and function is a function or
After visiting a file,
set-auto-mode calls function if
the text at the beginning of the buffer matches regexp and
function is non-
nil; if function is
auto-mode-alist gets to decide the mode.
This works like magic-mode-alist, except that it is handled only if auto-mode-alist does not specify a mode for this file.
This variable contains an association list of file name patterns
(regular expressions) and corresponding major mode commands. Usually,
the file name patterns test for suffixes, such as ‘.el’ and
‘.c’, but this need not be the case. An ordinary element of the
alist looks like
(regexp . mode-function).
(("\\`/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode)
("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) …)
When you visit a file whose expanded file name (see File Name Expansion), with version numbers and backup suffixes removed using
file-name-sans-versions (see File Name Components), matches
set-auto-mode calls the corresponding
mode-function. This feature enables Emacs to select the proper
major mode for most files.
If an element of auto-mode-alist has the form
function t), then after calling function, Emacs searches
auto-mode-alist again for a match against the portion of the file
name that did not match before. This feature is useful for
uncompression packages: an entry of the form
function t) can uncompress the file and then put the uncompressed
file in the proper mode according to the name sans ‘.gz’.
Here is an example of how to prepend several pattern pairs to auto-mode-alist. (You might use this sort of expression in your init file.)
(setq auto-mode-alist (append ;; File name (within directory) starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("/[^\\./]*\\'" . fundamental-mode) ;; File name ends in ‘.C’. ("\\.C\\'" . c++-mode)) auto-mode-alist))