MAC OS reverse lookup IP list

ip_resolver.sh

#!/bin/sh
#
# @Description: MAC OS script to quickly reverse lookup host IP's to
#   DNS hostnames and print in a format compatible with copying
#   to Excel.
#
# @author: Zach Jetson
#

usage() {
	echo "Usage: $0 iplist"
	echo "\tiplist is a text file of ips seperated by new lines"
	exit 1
}

if [ $# -lt 2 ]; then
    usage
fi

while read IP ; do
	[ -z "$IP" ] && continue
    LOOKUP_RES=$(host $IP 2> /dev/null | sed -n 's/.*name pointer \(.*\)\./\1/p')
    test -z "$LOOKUP_RES" && LOOKUP_RES="- not found -"
    echo "$IP\t$LOOKUP_RES"
done < $1