my ($unique, $duplicate) = unique_and_duplicate(-List=> $list, -New_List => \@new_list);

This is used to mass add and remove email addresses from a list, it takes a array ref full of new email addresses, and see if they are already in the list.

my ($unique_ref, $duplicate_ref) = weed_out_subscribers(-List => $list,
-Path => $FILES,
-Type => 'list',
-New_List => \@addresses,
);