GNU bug report logs - #11815
24.1; Confusing behavior of & in Dired

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From: Juri Linkov <juri <at> jurta.org>
To: 11815 <at> debbugs.gnu.org
Subject: bug#11815: 24.1; Confusing behavior of & in Dired
Date: Wed, 11 Jul 2012 12:21:23 +0300

> I think that the following equivalence should hold:
>
>     ! COMMAND & == & COMMAND

The problem is that the equivalence should be rather following:

    & COMMAND == ! COMMAND * &

because the file names should be stuffed before the ampersand.

And also:

    & COMMAND * == ! COMMAND * &

    & COMMAND * ARG2 == ! COMMAND * ARG2 &

A reliable fix consistent with the usage of `*' and `?' would be:

=== modified file 'lisp/dired-aux.el'
--- lisp/dired-aux.el	2012-04-17 01:52:00 +0000
+++ lisp/dired-aux.el	2012-07-11 09:11:48 +0000
@@ -556,8 +556,9 @@ (defun dired-do-async-shell-command (com
       (dired-read-shell-command "& on %s: " current-prefix-arg files)
       current-prefix-arg
       files)))
-  (unless (string-match "[*?][ \t]*\\'" command)
-    (setq command (concat command " *")))
+  (if (and (not (string-match dired-quark-subst-regexp command))
+	   (not (string-match dired-star-subst-regexp command)))
+      (setq command (concat command " *")))
   (unless (string-match "&[ \t]*\\'" command)
     (setq command (concat command " &")))
   (dired-do-shell-command command arg file-list))

But then what to do with `?'?

    & COMMAND ? == ! COMMAND FILE1 & COMMAND FILE2 &

or

    & COMMAND ? == ! COMMAND FILE1 ; COMMAND FILE2 &

This is why we have bug#10598.

The following comment in dired-aux.el provides a useful hint
about the history of this function:

  ;; The in-background argument is only needed in Emacs 18 where
  ;; shell-command doesn't understand an appended ampersand `&'.

`in-background' is the former argument of `dired-do-shell-command'
removed by revno 911.  It could be revived, but its drawback is that
this argument should be added to many functions.

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