Use CLI package to make address an argument

what-is-my-ip.go

@@ -6,12 +6,35 @@ import (
 	"log"
 	"net"
 	"net/http"
+	"os"
+
+	"github.com/urfave/cli"
 )
 
 func main() {
+	app := cli.NewApp()
+	app.Name = "what-is-my-ip"
+	app.Version = "0.1.0"
+	app.Usage = "Webapp that gives the IP address for incoming requests"
+	app.Action = action
+
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name:   "address, a",
+			Value:  ":3000",
+			EnvVar: "WHAT_IS_MY_IP_ADDRESS",
+			Usage:  "Address and port to bind to",
+		},
+	}
+
+	app.Run(os.Args)
+}
+
+func action(c *cli.Context) error {
 	http.HandleFunc("/", getIP)
-	fmt.Println("listening on port 3000")
+	address := c.String("address")
-	http.ListenAndServe(":3000", nil)
+	fmt.Printf("listening on %s\n", address)
+	return http.ListenAndServe(address, nil)
 }
 
 func getIP(w http.ResponseWriter, req *http.Request) {