Add usage info to plymouth-set-default-plugin

diff --git a/scripts/plymouth-set-default-plugin.in b/scripts/plymouth-set-default-plugin.in
index 473221b3ed227b5b38a9257b50123cda637232d9..224c58ff217e6d155832202cb1855e265d7b9200 100755 (executable)
--- a/scripts/plymouth-set-default-plugin.in
+++ b/scripts/plymouth-set-default-plugin.in
@@ -14,6 +14,11 @@ fi
 [ -z "$LIBDIR" ] && LIBDIR="/usr/$LIB"
 [ -z "$BINDIR" ] && BINDIR="/usr/bin"
 
+function usage ()
+{
+  echo "usage: plymouth-set-default-plugin { --reset | <plugin-name> }"
+}
+
 if [ $# -lt 1 ]; then
         PLUGIN_NAME=$(basename $(readlink ${LIBDIR}/plymouth/default.so) .so)
         if [ -z "$PLUGIN_NAME" ]; then
@@ -29,6 +34,11 @@ if [ `id -u` -ne 0 ]; then
         exit 1
 fi
 
+if [ $# -ne 1 ]; then
+        echo $(usage) > /dev/stderr
+        exit 1
+fi
+
 PLUGIN_NAME=$1
 if [ $1 = '--reset' ]; then
         PLUGIN_NAME=$(basename $(ls -1 -t ${LIBDIR}/plymouth/*.so 2> /dev/null | grep -v default.so | tail -n 1) .so)