add -version flag & update help text

config/cli.go

@@ -6,29 +6,53 @@ import (
 	"os"
 )
 
-var (
-	filename string
-)
+var filename string
+const applicationName = "traefik-etcd-advertiser"
+
+func setupHelpMessage() {
+	flag.Usage = func() {
+		helpMessage()
+	}
+}
+
+func helpMessage() {
+	fmt.Fprintf(os.Stderr, "Usage:\n  %s [OPTIONS]\n\n", applicationName)
+	fmt.Fprintf(os.Stderr, "Options:\n")
+
+	flag.PrintDefaults()
+	fmt.Fprintf(os.Stderr, "\nHelp Options:\n  -h, --help\tShow this help message")
+}
+
+func printVersion(v string) {
+	fmt.Printf("Version: %s\n", v)
+}
+
+func ParseCli(version string) (string, *bool) {
+	setupHelpMessage()
 
-func ParseCli() (string, *bool) {
 	flag.StringVar(&filename, "filename", "", "path of config")
 	publish := flag.Bool("publish", false, "publish etcd messages")
+	versionFlag := flag.Bool("version", false, "print version information")
 
 	flag.Parse()
 
 	args := os.Args[1:]
+	if *versionFlag {
+		printVersion(version)
+		os.Exit(0)
+	}
+
 	if len(args) == 0 {
 		// no command, exit with code 2 (invalid usage)
-	  fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
+		helpMessage()
 
-    flag.PrintDefaults()
 		os.Exit(2)
 	}
 
 	if len(filename) < 1 {
 		fmt.Fprintf(os.Stderr, "Filename required. Usage:\n")
 
-		flag.PrintDefaults()
+		helpMessage()
 		os.Exit(2)
 	}