In HTML forms, there's a widget that supports multiple selections. You can pick more than one if you use CTRL+click or whatever your OS/GUI/browser widget implementation allows.

The secret is the scrolling_list() subroutine in CGI.pm.

In any modern installation of Perl, just type 'perldoc CGI' at the command line, and you'll be in business.

If that's not really want you're looking for (simplify), I would just assign the parameters to a hash, which will get rid of duplicates. Then just iterate over the keys and grab the values. That's a FAQ somewhere.