use Socket;

$net = "192.168.0.0";
$mask = "255.255.255.240";
$ip = "192.168.0.5";

print "$ip belongs to $net/$mask\n" if ((net2long($ip) & net2long($mask)) == net2long($net));

sub net2long {

  return unpack("N", inet_aton(shift));

}