bug#48072: 28.0.50: dired-read-shell-command: handle empty input properly [PATCH]

[Boruch Baum <boruch_baum@gmx.com>]

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Function dired-read-shell-command was accepting an empty input. This is
a bug because it then passes the empty input as a legitimate command
which is silently processed (in error) by dired, eventually to return a
completion message.

The attached patch fixes that, and also validates the entered command as
a valid shell executable.

--
hkp://keys.gnupg.net
CA45 09B5 5351 7C11 A9D1  7286 0036 9E45 1595 8BC0

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diff --git a/dired-aux.el b/dired-aux.el
index 1c10990..7f5775c 100644
--- a/dired-aux.el
+++ b/dired-aux.el
@@ -674,15 +674,22 @@ This normally reads using `read-shell-command', but if the
 offer a smarter default choice of shell command."
   (minibuffer-with-setup-hook
       (lambda ()
-	(setq-local dired-aux-files files)
-	(setq-local minibuffer-default-add-function
-		    #'minibuffer-default-add-dired-shell-commands))
+        (setq-local dired-aux-files files)
+        (setq-local minibuffer-default-add-function
+                    #'minibuffer-default-add-dired-shell-commands))
     (setq prompt (format prompt (dired-mark-prompt arg files)))
-    (if (functionp 'dired-guess-shell-command)
-	(dired-mark-pop-up nil 'shell files
-			   'dired-guess-shell-command prompt files)
-      (dired-mark-pop-up nil 'shell files
-			 'read-shell-command prompt nil nil))))
+    (let (command)
+      (setq command
+        (if (functionp 'dired-guess-shell-command)
+          (dired-mark-pop-up nil 'shell files
+                             'dired-guess-shell-command prompt files)
+         (dired-mark-pop-up nil 'shell files
+                            'read-shell-command prompt nil nil)))
+      (when (string-empty-p command)
+        (user-error "No command entered. Nothing to do!"))
+      (unless (executable-find command)
+        (user-error "Not a valid command!"))
+      command)))

 ;;;###autoload
 (defun dired-do-async-shell-command (command &optional arg file-list)