2007-10-26 John Wiegley <johnw@newartisans.com>

	* eshell/em-unix.el (eshell/diff): Before calling the `diff'
	function, ensure that the third argument is turned into a NIL if
	the string is otherwise completely empty (either no characters, or
	all tabs/spaces).  This fixes a bug from a user who found himself
	unable to customize `diff-switches' and still use Eshell's diff
	command.

1 files changed, 9 insertions, 1 deletions

diff --git a/lisp/eshell/em-unix.el b/lisp/eshell/em-unix.el
index 850d51dcac5..384fa083947 100644
--- a/lisp/eshell/em-unix.el
+++ b/lisp/eshell/em-unix.el
@@ -974,6 +974,13 @@ Show wall-clock time elapsed during execution of COMMAND.")
   (if eshell-diff-window-config
       (set-window-configuration eshell-diff-window-config)))
 
+(defun nil-blank-string ( string )
+  "if a string is all blanks return nil, if there are non-blank characters
+return the string"
+  (cond
+   ((string-match "[^[:blank:]]" string ) string)
+   (nil)))
+
 (defun eshell/diff (&rest args)
   "Alias \"diff\" to call Emacs `diff' function."
   (let ((orig-args (eshell-stringify-list (eshell-flatten-list args))))
@@ -995,7 +1002,8 @@ Show wall-clock time elapsed during execution of COMMAND.")
           (setcdr (last args 3) nil))
         (with-current-buffer
             (condition-case err
-                (diff old new (eshell-flatten-and-stringify args))
+                (diff old new
+                      (nil-blank-string (eshell-flatten-and-stringify args)))
               (error
                (throw 'eshell-replace-command
                       (eshell-parse-command "*diff" orig-args))))