more improvements to shw

shw

@@ -4,8 +4,11 @@
 if [[ ! -t 0 ]]; then
     less -FX
 # if there is only one arg and it is not a directory, less it
-elif [[ -z "$2" && ! -d "$1" ]]; then
+elif [[ "$#" -eq 1 && ! -d "$1" ]]; then
     less -FX "$1"
+# if there are exactly two arguments and neither is a directory, diff them
+elif [[ "$#" -eq 2 && ! -d "$1" && ! -d "$2" ]]; then
+    diff --color=auto -u "$@"
 # otherwise, run dir
 else
     ls -lhAF --color=auto "$@"