#!/bin/perl
#Output the IP address and fully qualified domain name of every host
#on the same network as the given host.
#The first argument is the hostname or IP address of a given host,
#e.g., i5.nyu.edu or 128.122.253.142
#The second argument is the number of network bits in the netmask, e.g., 26

use Socket;

if (@ARGV != 2) {
        die "$0: requires 2 arguments";
}

$begin = $ARGV[0];
$end  = $ARGV[1];   #number of network bits in the bitmask

$ipbegin = inet_aton($begin)
        or die "$0: argument $hostname must be a hostname or dotted IP address";

$ipend = inet_aton($end)
        or die "$0: argument $hostname must be a hostname or dotted IP address";

$ibegin = unpack('N', $ipbegin);
$iend = unpack('N', $ipend);

for ($i = $ibegin + 1; $i <= $iend; ++$i) {
	$ip = pack('N', $i);
	$name = gethostbyaddr($ip, AF_INET);
	if (defined $name) {
		print inet_ntoa($ip), ' ', $name, "\n";
	}
}

exit 0;