#!/bin/bash

set -e

usage() {
  echo "Runs nslookup on a list of domains given by a text file, each domain separated by a newline."
  echo "Usage: path_to_textfile.txt"
  exit 1
}

# call usage() function if no file name is supplied
[[ $# -eq 0 ]] && usage

while read line
do
  domain_name=$line
  domain_resolve=`nslookup $domain_name | grep -m 1 Name: | awk '{print $2}'`
  echo -e "$domain_name\t$domain_resolve"
done < $1