I can't help but wonder what you plan to be doing with the IP addresses in $hacklist...

In any event, the line should probably read:

$octet ||= $_ if /(\d{1,3}\.){3}\d{1,3}/;
[download]

update: sorry for jumping the gun -- I can see from your response to kschwab that you are parsing an IDS log, not endeavoring to create one ;)

   MeowChow                                   
               s aamecha.s a..a\u$&owag.print