use File::Tail ();

{
   local *CATLOG;

   if ($opt{'c'}) {
      open CATLOG, '<', $MAILLOG
         or die("Unable to open mail log: $!\n");
   } else {
      tie *CATLOG, 'File::Tail', (name => $MAILLOG, tail => -1);
   }

   while (<CATLOG>) {
      ...while loop code here...
   }
}