$ perl -MWWW::Mechanize::Shell -eshell

(no url)>get http://www.bioinformatics.nl/.../primer3plus.cgi
Retrieving http://www.bioinformatics.nl/.../primer3plus.cgi(200)

http://www.bioinformatics.nl/.../primer3plus.cgi> forms
Form [1]
POST http://www.bioinformatics.nl/.../primer3plus.cgi
(multipart/form-data) [mainForm]

... snip list of fields and default values where relevant ...