Emacs: Set Default Major Mode
Set Default Major Mode for New Empty Buffer
Put this in your Emacs Init File:
(setq initial-major-mode 'js-mode)
Associate Major Mode by File Name Extension
Use auto-mode-alist to associate a major mode with file name extension.
;; setup files ending in “.js” to open in xah-js-mode (add-to-list 'auto-mode-alist '("\\.js\\'" . xah-js-mode))
auto-mode-alist is a built-in variable. Its value is a Association List . Each key is a regex string, and value is mode name symbol. [see Emacs: Show Variable Value, List Variables]
[see Emacs: Regular Expression]
Remove File Extension Association
You can remove file name association with a major mode. Example:
;; remove any file name suffix associated with js-mode (setq auto-mode-alist (rassq-delete-all 'js-mode auto-mode-alist))
To check if a mode is in the list, eval the following.
;; check if js-mode is in the list (rassoc 'js-mode auto-mode-alist)
[see Evaluate Emacs Lisp Code]
Normally, you do not need to remove items in
. Simply add to the front using
Associate Major Mode by First Line in File
The magic-mode-alist is variable with value a Association List, for associating first line of a file with a mode. [see Emacs: Show Variable Value, List Variables] Use it like this:
;; if first line of file matches, activate nxml-mode (add-to-list 'magic-mode-alist '("<!DOCTYPE html .+DTD XHTML .+>" . nxml-mode) )
How Emacs Determines Which Major Mode to Load
Emacs determines what mode to activate by the following mechanisms, in order. If a match is found, the process stops.
- Look for a special emacs-specific syntax in the file. For example: if first line in the file contains
-*- mode: xyz-*-, emacs will load “xyz-mode”. This is from a general mechanism for emacs to load elisp variables. (See: (info "(emacs) File Variables").) This has the top priority, but this mechanism is not the usual way for programing language files to associate with a major mode.
- Check the first line in the file for unix “shebang” syntax (For example,
#!/usr/bin/perl) and match it with interpreter-mode-alist.
- Trys to match first line text with magic-mode-alist. (As of emacs 24.1.1, by default this list is empty.)
- Match the file name with auto-mode-alist.
(info "(emacs) Choosing Modes")
Note that when you install a new package, some has the file association setting code within the package, while others ask you to put a few lines in your emacs init file instead.