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

Ray
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9 Answers9

180

M-x read-only-mode

in very old versions of Emacs, the command was:

M-x toggle-read-only

On my Windows box, that amounts to Alt-x to bring up the meta prompt and typing "read-only-mode" 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.

Following up from the commentary: you should note that the writeable status of the buffer does not change the writeable permission of the file. If you try to write out to a read only file, you'll see a confirmation message. However, if you own the file, you can write out your changes without changing the permissions on the file.

This is very convenient if you'd like to make a quick change to a file without having to go through the multiple steps of add write permission, write out changes, remove write permission. I tend to forget that last step, leaving potentially critical files open for accidental changes later on.

mit
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Bob Cross
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    Hi, as stated in the answer from jfm3 `toggle-read-only` only toggles the read only state of the buffer not of the file. If you want to change the mode of the file use `dired` or execute `chmod +w` as a shell command on the file. – danielpoe Feb 25 '09 at 08:56
  • True, that is how you would change the mode. However, if you toggle read-only mode on a buffer that points at a read-only file that you own, you will be able to edit it and write out your changes (there will be a confirmation question, of course). – Bob Cross Feb 26 '09 at 00:04
  • Followed-up on the comments above and added text to the answer. – Bob Cross Sep 26 '12 at 13:02
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    In recent versions of Emacs, toggle-read-only has been replaced with read-only-mode. – Benilda Key May 19 '15 at 18:35
15

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.

jfm3
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13

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

Dmytro Kuznetsov
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8

CTRL + X + CTRL + Q     

Tushar
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anjanb
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7

As mentioned up there by somebody else: M-x toggle-read-only would work.

However, this is now deprecated and M-x read-only-mode is the current way to do it, that it is set to C-x C-q keybinding.

Borja Tarraso
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6

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)))
       (set-buffer output-buffer)
       (save-excursion 
         (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))
  (substring 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.

Vebjorn Ljosa
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  • When I try to compile my .emacs with this code, I get the message "Warning: save-excursion defeated by set-buffer". – Alan Mar 04 '13 at 18:23
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    @Alan, edited to put the `set-buffer` outside the `save-excursion`. – Vebjorn Ljosa Mar 05 '13 at 16:18
  • thanks for that change, which eliminated the warning. However, there's another one: "Warning: Function `subseq' from cl package called at runtime." I couldn't get rid of that even when I added (eval-when-compile (require 'cl)) to my .emacs. – Alan Mar 06 '13 at 15:25
  • See [this thread](http://comments.gmane.org/gmane.emacs.help/10422). I have edited the code and replaced `subseq` with `substring` now. That should avoid the warning. – Vebjorn Ljosa Mar 06 '13 at 19:03
  • Now that I've gone over to Emacs 24, I get the message "Warning: the function `decf' is not known to be defined." – Alan Mar 31 '14 at 17:21
  • Try `(require 'cl-lib)` instead of `(eval-when-compile (require 'cl))`. – Vebjorn Ljosa Mar 31 '14 at 17:47
  • When I use (require 'cl-lib), I still get the same warning. Note that I previously had no require statement for either cl or cl-lib. – Alan Mar 31 '14 at 18:13
3

If you are looking at a directory of files (dired), then you can use Shift + M on a filename and enter the modespec, the same attributes used in the chmod command.
M modespec <RET>

See the other useful commands on files in a directory listing at http://www.gnu.org/s/libtool/manual/emacs/Operating-on-Files.html

manas
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Louis Roehrs
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0

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.

0

C-x C-q is useless. Because your also need the permission to save a file.

I use Spacemacs. It gives me a convenient function to solve this question. The code is following.

(defun spacemacs/sudo-edit (&optional arg)
  (interactive "p")
  (if (or arg (not buffer-file-name))
      (find-file (concat "/sudo:root@localhost:" (ido-read-file-name "File: ")))
    (find-alternate-file (concat "/sudo:root@localhost:" buffer-file-name))))

I call spacemacs/sudo-edit to open a file in emacs and input my password, I can change the file without read-only mode.

You can write a new function like spacemacs/sudo-edit.

Li Tianyi
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