#!/bin/sh
#
#	IP NameServerLookup
#
#	Look up the host name for an IP.
#	Output will be IP<TAB>HOSTNAME if nslookup is successful.
#
#	Brent Chivers						2020/Nov/18
#	Smarter code.						2020/Nov/20
#	Improved formatting for IPs with multiple hostnames.	2022/Feb/20
#
# Frequent use will be "sort IPList | uniq -c | ipnsl"		2020/Dec/29
# If there's an integer (not an IP) echo it through with a TAB and no NEWLINE.
# (Output will be COUNT<TAB>IP or COUNT<TAB>IP<TAB>HOSTNAME.)
# Doesn't recognize integers more than 7 digits. Could add recognizing numbers w/ commas.

for IP in `cat $*` ; do
	case $IP in
	    [0-9] | [0-9][0-9] | [0-9][0-9][0-9] | [0-9][0-9][0-9][0-9] | [0-9][0-9][0-9][0-9][0-9] | [0-9][0-9][0-9][0-9][0-9][0-9] | [0-9][0-9][0-9][0-9][0-9][0-9][0-9] )
		echo "$IP	\c"
		;;
	    * )
		NAME=`/usr/bin/nslookup $IP | /bin/grep 'name = ' | /bin/sed 's/.*name = /	/'`
		echo "$IP$NAME" | /bin/sed 's/^	/		/'
		;;
	    esac
    done