+if [ $# -eq 3 ]; then
+ [ -d "$1/$3" ] && [ -d "$2/$3" ] &&
+ exit
+ [ ! -e "$1/$3" ] && [ ! -e "$2/$3" ] &&
+ echo "$0: something wrong abount '$3'" >&2 && exit
+ [ -e "$1/$3" ] && [ ! -e "$2/$3" ] &&
+ echo "Only in '$1': '$3'" >&2 && exit
+ [ ! -e "$1/$3" ] && [ -e "$2/$3" ] &&
+ echo "Only in '$2': '$3'" >&2 && exit
+ [ -f "$1/$3" ] && [ -d "$2/$3" ] &&
+ echo "'$1/$3' is a regular file but '$2/$3' is a directory" >&2 && exit
+ [ -d "$1/$3" ] && [ -f "$2/$3" ] &&
+ echo "'$1/$3' is a directory but '$2/$3' is a regular file" >&2 && exit
+
+ cmp -s "$1/$3" "$2/$3" || echo "$1/$3" "$2/$3" are differ >&2
+ exit
+fi