Print usage when argv empty

docker_custodian/docker_autostop.py

@@ -95,6 +95,10 @@ def get_opts(args=None):
     )
     opts = parser.parse_args(args=args)
 
+    if len(sys.argv) < 2:
+        parser.print_help()
+        exit(0)
+
     if not opts.prefix:
         parser.error("Running with no --prefix will match nothing.")
 

docker_custodian/docker_gc.py

@@ -269,6 +269,10 @@ def get_args(args=None):
         help="Path to a file which contains a list of images to exclude, one "
              "image tag per line.")
 
+    if len(sys.argv) < 2:
+        parser.print_help()
+        exit(0)
+
     return parser.parse_args(args=args)