Allow commands to return error codes.

bin/spack

@@ -103,7 +103,7 @@ if args.insecure:
 # Try to load the particular command asked for and run it
 command = spack.cmd.get_command(args.command)
 try:
-    command(parser, args)
+    return_val = command(parser, args)
 except SpackError, e:
     if spack.debug:
         # In debug mode, raise with a full stack trace.
@@ -116,3 +116,11 @@ except SpackError, e:
 except KeyboardInterrupt:
     sys.stderr.write('\n')
     tty.die("Keyboard interrupt.")
+
+# Allow commands to return values if they want to exit with some ohter code.
+if return_val is None:
+    sys.exit(0)
+elif isinstance(return_val, int):
+    sys.exit(return_val)
+else:
+    tty.die("Bad return value from command %s: %s" % (args.command, return_val))

lib/spack/spack/cmd/graph.py

@@ -31,6 +31,8 @@
 description = "Generate graphs of package dependency relationships."
 
 def setup_parser(subparser):
+    setup_parser.parser = subparser
+
     method = subparser.add_mutually_exclusive_group()
     method.add_argument(
         '--ascii', action='store_true',
@@ -50,6 +52,9 @@ def graph(parser, args):
     specs = spack.cmd.parse_specs(
         args.specs, normalize=True, concretize=args.concretize)
 
+    if not specs:
+        setup_parser.parser.print_help()
+        return 1
 
     if args.dot:    # Dot graph only if asked for.
         graph_dot(*specs)

lib/spack/spack/cmd/md5.py

@@ -41,6 +41,7 @@ def setup_parser(subparser):
 def md5(parser, args):
     if not args.files:
         setup_parser.parser.print_help()
+        return 1
 
     for f in args.files:
         if not os.path.isfile(f):