add some basic error handling to 'weave' script

weaver/weave

@@ -8,7 +8,15 @@ MTU=65535
 SCRIPT_DIR=$(dirname $(readlink -f $0))
 COMMAND=$1
 IPADDR=$2
-shift 2
+
+usage() {
+    echo "Usage:"
+    echo "weave <ipaddr>/<subnet> launch [-passwd <passwd>] <peer_host> ..."
+    echo "weave <ipaddr>/<subnet> run <docker run args> ..."
+    exit 1
+}
+
+shift 2 || usage
 
 # pre-create bridge so we can set the MTU
 [ ! -d /sys/class/net/$BRIDGE ] && {
@@ -40,6 +48,10 @@ case "$COMMAND" in
         CONTAINER=$(docker run -d "$@")
         IFACE=$CONTAINER_IFNAME
         ;;
+    *)
+        echo "Unknown weave command '$COMMAND'"
+        usage
+        ;;
 esac
 
 # the following borrows from https://github.com/jpetazzo/pipework