cli: Lookup host on init unless ip given

cli/cli.go

@@ -1,8 +1,9 @@
 package cli
 
 import (
-	"errors"
 	"fmt"
+	"log"
+	"net"
 	"sync"
 	"time"
 
@@ -30,16 +31,22 @@ var (
 
 // rootCmd represents the root command
 var RootCmd = &cobra.Command{
-	Use: "mtr TARGET",
+	Use:  "mtr TARGET",
+	Args: cobra.ExactArgs(1),
 	RunE: func(cmd *cobra.Command, args []string) error {
 		if versionFlag {
 			fmt.Printf("MTR Version: %s, build date: %s\n", version, date)
 			return nil
 		}
-		if len(args) != 1 {
-			return errors.New("No target provided")
+		ip := args[0]
+		if net.ParseIP(args[0]) == nil {
+			addrs, err := net.LookupHost(args[0])
+			if err != nil || len(addrs) == 0 {
+				log.Fatalf("invalid host or ip provided: %s", err)
+			}
+			ip = addrs[0]
 		}
-		m, ch := mtr.NewMTR(args[0], srcAddr, TIMEOUT, INTERVAL, HOP_SLEEP, MAX_HOPS, MAX_UNKNOWN_HOPS, RING_BUFFER_SIZE)
+		m, ch := mtr.NewMTR(ip, srcAddr, TIMEOUT, INTERVAL, HOP_SLEEP, MAX_HOPS, MAX_UNKNOWN_HOPS, RING_BUFFER_SIZE)
 		if jsonFmt {
 			go func(ch chan struct{}) {
 				for {