#!/bin/bash
if [ -z "$1" ]
then
    echo "You must specify a filename to read from"
    exit 1;
fi
if [ ! -f "$1" ]
then
    echo "File $1 does not exist or is not a file"
    exit 1;
fi
while read ip n
do
   # Uncomment following to use /etc/hosts
   # name=$(awk -v ip=$ip '$1 ~ ip{print $2}' /etc/hosts)
   # Uncomment following to use nslookup
   # name=$(nslookup $ip| grep "name ="|sed 's/.*=//')
   # Uncomment following line to use dig (thanks to Charles Duffy)
   #name=$(dig +short -x $ip)i
   if [ -z "$2" ]
   then
   resolvedIP=$(dig +short +x "$ip")
   else
   resolvedIP=$(dig +short +x "$ip" "$2")
   fi
   [[ -z "$resolvedIP" ]] && echo "$ip" lookup failure || echo "$ip" resolved to "$resolvedIP"
done < $1