add command usage.

Signed-off-by: Bo-Yi Wu <appleboy.tw@gmail.com>

gorush.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"flag"
+	"fmt"
 	"github.com/appleboy/gorush/config"
 	"github.com/appleboy/gorush/gorush"
 	"log"
@@ -20,6 +21,34 @@ func checkInput(token, message string) {
 
 var Version = "No Version Provided"
 
+var usageStr = `
+Usage: gorush [options]
+
+Server Options:
+    -p, --port <port>                Use port for clients (default: 8088)
+    -c, --config <file>              Configuration file
+    -m, --message <message>          Notification message
+    -t, --token <token>              Notification token
+iOS Options:
+    -i, --pem <file>                 certificate key file path
+    -P, --password <password>        certificate key password
+    --topic <topic>                  iOS topic
+    --ios                            enabled iOS (default: false)
+    --production                     iOS production mode (default: false)
+Android Options:
+    -k, --key <api_key>              Android API Key
+    --android                        enabled android (default: false)
+Common Options:
+    -h, --help                       Show this message
+    -v, --version                    Show version
+`
+
+// usage will print out the flag options for the server.
+func usage() {
+	fmt.Printf("%s\n", usageStr)
+	os.Exit(0)
+}
+
 func main() {
 	opts := config.ConfYaml{}
 
@@ -34,20 +63,31 @@ func main() {
 	flag.StringVar(&configFile, "c", "", "Configuration file.")
 	flag.StringVar(&configFile, "config", "", "Configuration file.")
 	flag.StringVar(&opts.Ios.PemPath, "i", "", "iOS certificate key file path")
+	flag.StringVar(&opts.Ios.PemPath, "pem", "", "iOS certificate key file path")
+	flag.StringVar(&opts.Ios.Password, "P", "", "iOS certificate password for gorush")
 	flag.StringVar(&opts.Ios.Password, "password", "", "iOS certificate password for gorush")
 	flag.StringVar(&opts.Android.APIKey, "k", "", "Android api key configuration for gorush")
+	flag.StringVar(&opts.Android.APIKey, "key", "", "Android api key configuration for gorush")
 	flag.StringVar(&opts.Core.Port, "p", "", "port number for gorush")
+	flag.StringVar(&opts.Core.Port, "port", "", "port number for gorush")
 	flag.StringVar(&token, "t", "", "token string")
+	flag.StringVar(&token, "token", "", "token string")
 	flag.StringVar(&message, "m", "", "notification message")
+	flag.StringVar(&message, "message", "", "notification message")
 	flag.BoolVar(&opts.Android.Enabled, "android", false, "send android notification")
 	flag.BoolVar(&opts.Ios.Enabled, "ios", false, "send ios notification")
 	flag.BoolVar(&opts.Ios.Production, "production", false, "production mode in iOS")
 	flag.StringVar(&topic, "topic", "", "apns topic in iOS")
 
+	flag.Usage = usage
 	flag.Parse()
 
 	gorush.SetVersion(Version)
 
+	if len(os.Args) < 2 {
+		usage()
+	}
+
 	// Show version and exit
 	if showVersion {
 		gorush.PrintGoRushVersion()