--- a/mk	Fri Sep 25 17:39:02 2015 +0100
+++ b/mk	Fri Sep 25 20:59:24 2015 +0100
@@ -1,7 +1,7 @@
 #!/bin/sh
 set -e
 
-subdirs="slides handouts hws coursework" 
+subdirs=${1:-"slides handouts hws coursework"} 
 
 for sd in $subdirs; do
   cd $sd