--- xflock4	2007-12-04 18:01:57.000000000 +0100
+++ xflock4.new	2008-10-05 14:53:19.000000000 +0200
@@ -19,11 +19,17 @@
 #  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 #
 
-if test x"`which xscreensaver-command 2>/dev/null`" != x""; then
+if which xscreensaver-command &>/dev/null; then
     xscreensaver-command -lock 
-elif test x"`which gnome-screensaver-command 2>/dev/null`" != x""; then
+elif which gnome-screensaver-command &>/dev/null; then
     gnome-screensaver-command --lock
-else
+elif which xlock &>/dev/null; then
     xlock $*
+else
+	echo "Could not find xscreensaver, gnome-screensaver or xlock.  I Cannot work without one of them." >&2
+	if which zenity &>/dev/null; then
+		zenity --error --title "Xflock4 error" --text "Could not find xscreensaver, gnome-screensaver or xlock.  I Cannot work without one of them."
+	fi
+	exit 1
 fi
 exit 0