Display usage information in case of unknown action.

sit

@@ -14,6 +14,24 @@ SIT_PATH=$(cd $(dirname $PWD/$0); pwd)
 SIT_CONFIG_FILE=$SIT_PATH/etc/sit.conf
 SIT_USER_CONFIG_FILE=$HOME/.sit
 
+function usage() {
+    echo "Usage: $0 [action] <sit package name>"
+    echo "Valid actions:"
+    echo "    sit_sitinfo"
+    echo "    unpack"
+    echo "    prepare"
+    echo "    configure"
+    echo "    build"
+    echo "    pretest"
+    echo "    install"
+    echo "    posttest"
+    echo "    postinst"
+    echo "    copy_logs"
+    echo "    setperms"
+    echo "    all"
+    exit 0
+}
+
 # sit action to be performed
 sit_action=$2
 if [[ -n $sit_action ]] ; then
@@ -263,6 +281,7 @@ case $sit_action in
 ;;
 *)
     echo "Unknown action $sit_action"
+    usage
 esac