Re: How to change and save a read-only file?

[Kevin Rodgers <kevin.d.rodgers@gmail.com>]

On 11/19/13 8:27 PM, Emanuel Berg wrote:
> It seems the thread that the subject refers to is
> inaccessible by Gnus, so perhaps the OP won't read this
> anyway, but I like to say it nonetheless, because this
> bug almost drove me insane.
>
> The below function cannot be used on symbolic links,
> because with (buffer-file-name), you'll get the name
> (and path) of the *link*...
>
> When used to edit and save such a link that points to a
> file not in $HOME, the result is that the link is
> *replaced* by the file, and the file (at its original
> place), disappears (?).
>
> The code, with the bug:
>
> (defun su-edit ()
>    "Edit the current buffer file as superuser."
>    (interactive)
>    (let ((window-start (window-start))
>          (point        (point))
>          (mark (if mark-active (region-beginning) nil)) )
>      (find-alternate-file (format "/sudo::%s" (buffer-file-name)))
>      (if mark (set-mark mark))
>      (goto-char point)
>      (set-window-start nil window-start) ; nil - the selected window
>      ))
>
> The solution, I hope, is:
> (file-truename (buffer-file-name))

See the "Rename or Copy" node (aka "Backup by Renaming or by Copying?")
in the Emacs Lisp manual: let-bind backup-by-copying to nil and
backup-by-copying-when-linked to t.

Also, see the interactions with backup-directory-alist that are explained in
the "Auto-save and Backup" node of the Tramp manual.

-- 
Kevin Rodgers
Denver, Colorado, USA