ptrhost.go

package main

import (
	"fmt"
	"net"
	"os"
)

func main() {
	host := os.Args[1]

	addrs, _ := net.LookupHost(host)

	for _, addr := range addrs {
		names, _ := net.LookupAddr(addr)

		fmt.Printf("%s ", addr)

		for _, name := range names {
			fmt.Println(name)
		}
	}
}