Path: utzoo!attcan!uunet!mfci!yale!Ram-Ashwin
From: Ram-Ashwin@cs.yale.edu (Ashwin Ram)
Newsgroups: comp.emacs
Subject: Re: mode by file contents
Message-ID: <48686@yale-celray.yale.UUCP>
Date: 25 Jan 89 19:45:04 GMT
References: <GHH.89Jan25110326@thought.princeton.edu>
Sender: root@yale.UUCP
Reply-To: Ram-Ashwin@cs.yale.edu (Ashwin Ram)
Organization: Computer Science, Yale University, New Haven, CT 06520-2158
Lines: 54
In-reply-to: ghh@thought.princeton.edu (Gilbert Harman)

In article <GHH.89Jan25110326@thought.princeton.edu>, ghh@thought.princeton.edu (Gilbert Harman) writes:
> I would like to put something in my .emacs that would
> determine the major mode of a buffer on the basis of the
> contents of the file read into the buffer rather than on the
> basis of something about the name of the file.
> 
> For example, if the file began with "\documentstyle... "
> the buffer would be automatically put into latex mode.

See if you like this.  To use, put this in your ~/.emacs file:

    (setq find-file-hooks '(infer-file-mode))

The function infer-file-mode uses infer-mode-alist (analogous to
auto-mode-alist) to search for a regexp within the first infer-mode-limit
characters (nil means search entire buffer).  In your example, you would use:

    (setq infer-mode-alist '(("\\documentstyle" . latex-mode)))

-----------------------------------------------------------------------------
;; INFER-MODE.EL -- Infer file mode based on contents.
;; Ashwin Ram, 11/5/88.

(defvar infer-mode-alist '(("\\documentstyle" . latex-mode))
   "Alist of file content patterns vs corresponding major mode functions.
Each element looks like (REGEXP . FUNCTION).
Visiting a file whose which contains REGEXP within the first infer-mode-limit
characters causes FUNCTION to be called.")

(defvar infer-mode-limit 1000
   "Number of characters to search when inferring mode based on file contents.
Nil means search entire buffer.  See infer-mode-alist.")

(defun infer-file-mode ()
   "Infer mode of file based on its contents.
To use, add this function to find-file-hooks.
To customize, see the variable infer-mode-alist."
   (let ((mode-alist infer-mode-alist))
      (catch 'found
         (while mode-alist
            (if (save-excursion
                   (goto-char (point-min))
                   (re-search-forward (caar mode-alist) infer-mode-limit t))
                (throw 'found t)
                (setq mode-alist (cdr mode-alist)))))
      (if mode-alist
          (funcall (cdar mode-alist)))))
-----------------------------------------------------------------------------

-- Ashwin.

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