Depending on your needs you may be able to use LWP::Simple.
Makes posting to a form very easy.

perl -MLWP::Simple -ne 'getprint("http://your_site.com/form.cgi?unsubs
+cribe=1&who=me" )'
[download]

Note though that any form variables that you want to submit to the form will have to be properly encoded.

Modules like URI::Escape can help with that though. :-)

Hope that helps.

Wonko