👍 Add interface flag

main.go

@@ -19,15 +19,33 @@ var (
 	handle       *pcap.Handle
 )
 
-func main() {
-	var device string = "lo"
+func findDevice(c *cli.Context) string {
+	if c.String("interface") != "" {
+		return c.String("interface")
+	}
+	devices, err := pcap.FindAllDevs()
+	if err != nil {
+		panic(err)
+	}
+
+	return devices[0].Name
+}
 
+func main() {
 	app := cli.NewApp()
 	app.Name = "tcpterm"
 	app.Usage = "tcpdump for human"
 	app.Version = "0.0.1"
 
+	app.Flags = []cli.Flag{
+		cli.StringFlag{
+			Name:  "interface, i",
+			Usage: "If unspecified, use lowest numbered interface.",
+		},
+	}
+
 	app.Action = func(c *cli.Context) error {
+		device := findDevice(c)
 		handle, err = pcap.OpenLive(device, snapshot_len, promiscuous, timeout)
 		if err != nil {
 			log.Fatal(err)