How to modify write permission on current buffer in emacs?

Question

Is it possible to change the write permissions on a file from inside emacs, without killing/re-opening the buffer?

Sometimes I forget to modify the permissions on a file before opening it. I can modify the permissions from inside emacs (M-! chmod u+w filename) but this doesn't update the buffer which remains write protected and refuses to modify the file.

Is there a way to update permissions inside the buffer? Bonus point if I can assign this to a shortcut!

Solution 1

After changing the file mode, and before doing any edit, run M-x revert-buffer to reload the file. If the file is now writable, the buffer will no longer be read-only.

Alternatively, type C-x C-q (read-only-mode). This makes the buffer no longer read-only. You can edit and even save, but you'll get a confirmation prompt asking whether you want to overwrite the read-only file.

Solution 2

To change the read-only status of a buffer, use C-xC-q (toggle read-only-mode). To change file permissions, you can run dired on the file's directory (C-xd), search for the file by C-s and use M to change its mode.

Solution 3

If the workflow requires to change the file permission of the buffer repeatedly, then having a custom function would help like the following.

This works only on unix machines(executes system command "chmod"

(defun chmod-plus-w ()
  (interactive)
  (shell-command-to-string (concat "chmod +w " (buffer-file-name (current-buffer))))
  (revert-buffer))

Comments

[cjm]

Apparently, you've missed dired-jump (normally bound to C-x C-j). It runs dired and jumps to the line for the file you're editing.

[choroba]

@cjm: It does not work for me unless I load dired-x.

[cjm]

Sorry, I'd forgotten that I'd set up an autoload for dired-jump about 20 years ago. I recommend it.

[Charlie Martin]

Annoyingly toggle-read-only has been replaced with read-only-mode, although the binding is the same.

[Hodaya Shalom]

While C-x C-q still works, as of emacs 24.3 it now calls read-only-mode rather than toggle-read-only and toggle-read-only has been disabled.