#!/bin/bash
IP4BLOCK="$1"

echo "Doing reverse lookup for $IP4BLOCK.0/24..."

ctr=1
while [ $ctr -le 255 ]; do
	ipaddress="$IP4BLOCK.$ctr";
	result=`dig +short -x $ipaddress`;
	result=`echo $result | sed -e 's#\n##g'`
	if [ "$result" != "" ]; then
		echo "$ipaddress $result";
	fi;
	((ctr++));
done