How do I change read/write mode for a file using Emacs?

Question

If a file is set to read only mode, how do I change it to write mode and vice versa from within Emacs?

Answer 1

M-x toggle-read-only

On my Windows box, that amounts to Alt-x to bring up the meta prompt and typing "toggle-read-only" to call the correct elisp function.

If you are using the default keyboard bindings,

C-x C-q

(which you read aloud as "Control-X Control-Q") will have the same effect. Remember, however, given that emacs is essentially infinitely re-configurable, your mileage may vary.

Answer 2

OR CTRL X + CTRL Q.

Answer 3

Be sure you're not confusing 'file' with 'buffer'. You can set buffers to read-only and back again with C-x C-q (toggle-read-only). If you have permission to read, but not write, a file, the buffer you get when you visit the file (C-x C-f or find-file) will be put in read-only mode automatically. If you want to change the permissions on a file in the file system, perhaps start with dired on the directory that contains the file. Documentation for dired can be found in info; C-h i (emacs)dired RET.

Answer 4

If only the buffer (and not the file) is read-only, you can use toggle-read-only, which is usually bound to C-x C-q.

If the file itself is read-only, however, you may find the following function useful:

(defun set-buffer-file-writable ()
  "Make the file shown in the current buffer writable.
Make the buffer writable as well."
  (interactive)
  (unix-output "chmod" "+w" (buffer-file-name))
  (toggle-read-only nil)
  (message (trim-right '(?\n) (unix-output "ls" "-l" (buffer-file-name)))))

The function depends on unix-output and trim-right:

(defun unix-output (command &rest args)
  "Run a unix command and, if it returns 0, return the output as a string.
Otherwise, signal an error.  The error message is the first line of the output."
  (let ((output-buffer (generate-new-buffer "*stdout*")))
    (unwind-protect
     (let ((return-value (apply 'call-process command nil
           output-buffer nil args)))
       (save-excursion 
         (set-buffer output-buffer)
         (unless (= return-value 0)
           (goto-char (point-min))
           (end-of-line)
           (if (= (point-min) (point))
        (error "Command failed: %s%s" command
        (with-output-to-string
            (dolist (arg args)
       (princ " ")
       (princ arg))))
        (error "%s" (buffer-substring-no-properties (point-min) 
                 (point)))))
         (buffer-substring-no-properties (point-min) (point-max))))
      (kill-buffer output-buffer))))

(defun trim-right (bag string &optional start end)
  (setq bag (if (eq bag t) '(?\  ?\n ?\t ?\v ?\r ?\f) bag)
    start (or start 0)
    end (or end (length string)))
  (while (and (> end 0)
          (member (aref string (1- end)) bag))
    (decf end))
  (subseq string start end))

Place the functions in your ~/.emacs.el, evaluate them (or restart emacs). You can then make the file in the current buffer writable with M-x set-buffer-file-writable.

Answer 5

I tried out Vebjorn Ljosa's solution, and it turned out that at least in my Emacs (22.3.1) there isn't such function as 'trim-right', which is used for removing an useless newline at the end of chmod output.

Removing the call to 'trim-right' helped, but made the status row "bounce" because of the extra newline.

Answer 6

What I found is M-x set-file-modes filename mode

It worked at my Windows Vista box. For example: M-x set-file-modes <RET> ReadOnlyFile.txt <RET> 0666