Are you really sure CGI isn't installed? It's included by default with most recent Perl distros, past 5.004 as chromatic pointed out. But if you're really stuck, take a look at the code in CGI.pm itself: it's better to build off of the right way to do it than reinvent the wheel incorrectly. Specifically, the code you need is in the init and parse_params subs.

The reason I'd suggest you modify existing code for your needs (or use it straight out if you can) is that it's difficult to handle all the possible query strings and a lot of people get it wrong (even many CGI books have flawed parameter parsers). For instance, what will your routine do when a user selects multiple items in a list box? Only the last will be saved, which is incorrect behavior. You may not have any such forms, and your code may work with your application, but look around for existing battle-tested implementations; turnstep posted one here in response to a Q&A post.