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bug#57795: FIXME about save-match-data in shell-command
From: |
Lars Ingebrigtsen |
Subject: |
bug#57795: FIXME about save-match-data in shell-command |
Date: |
Wed, 14 Sep 2022 15:25:35 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/29.0.50 (gnu/linux) |
Stefan Kangas <stefankangas@gmail.com> writes:
> In `shell-command', we have the following comment:
>
> ;; Preserve the match data in case called from a program.
> ;; FIXME: It'd be ridiculous for an Elisp function to call
> ;; shell-command and assume that it won't mess the match-data!
>
> I think we should decide to either get rid of the FIXME, or to take the
> plunge and remove `save-match-data'. (Note that the latter has been
> there since 1995.)
Hm -- I originally thought that removing that save-match-data would lead
to subtle errors in callers that depend on this behaviour.
But... there's also code like
(let ((handler
(find-file-name-handler (directory-file-name default-directory)
'shell-command)))
(if handler
(funcall handler 'shell-command command output-buffer error-buffer)
(if (and output-buffer
(not (string-match "[ \t]*&[ \t]*\\'" command))
before that save-match-data, so the match data will be overwritten in
many cases anyway.
The code was (originally in 1991):
+(defun shell-command (command &optional flag)
+ "Execute string COMMAND in inferior shell; display output, if any.
+If COMMAND ends in ampersand, execute it asynchronously.
+
+Optional second arg non-nil (prefix arg, if interactive)
+means insert output in current buffer after point (leave mark after it).
+This cannot be done asynchronously."
+ (interactive (list (read-string "Shell command: " last-shell-command)
+ current-prefix-arg))
+ (if flag
+ (progn (barf-if-buffer-read-only)
+ (push-mark)
+ ;; We do not use -f for csh; we will not support broken use of
+ ;; .cshrcs. Even the BSD csh manual says to use
+ ;; "if ($?prompt) exit" before things which are not useful
+ ;; non-interactively. Besides, if someone wants their other
+ ;; aliases for shell commands then they can still have them.
+ (call-process shell-file-name nil t nil
+ "-c" command)
+ (exchange-point-and-mark))
+ ;; Preserve the match data in case called from a program.
+ (let ((data (match-data)))
And here we see that the command does really preserve the match data in
all circumstances -- but that has been lost over the years.
So I think removing the save-match-data should probably not lead to any
regressions, so I've now removed it.