add Setup function

setup.go

@@ -0,0 +1,30 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flag
+
+import (
+	"fmt"
+	"os"
+)
+
+// Setup parses flag and setups usage function.
+// `positionalArgs` is a string representing positional args, eg: "arg1 arg2 arg3"
+// `commands` if provided is a positional argument command description.
+func Setup(version, positionalArgs string, commands ...string) {
+	Usage = func() {
+		fmt.Fprintln(os.Stderr, "Version: ", version)
+		if len(commands) != 0 {
+			fmt.Fprintf(os.Stderr,
+				"USAGE: %s <commands> <parameters> %s\n\n", os.Args[0], positionalArgs)
+			fmt.Fprint(os.Stderr, "COMMANDS:", commands[0], "\n\n")
+		} else {
+			fmt.Fprintf(os.Stderr,
+				"USAGE: %s <parameters> %s\n\n", os.Args[0], positionalArgs)
+		}
+		fmt.Fprintln(os.Stderr, "PARAMETERS:")
+		PrintDefaults()
+	}
+	Parse()
+}