If FOO.html is meant to be dynamic, then perhaps what you might want to do is put the FOO.html contents in BAR.pl and have BAR.pl print the FOO contents, which would change depending on the form field contents.

This way you don't have to maintain/edit the FOO.html file seperately (and updating the static page could get ugly... so if you do this contemplate using a perl templating module)

also, what if more than one person is using the site? Modifying FOO.html in a multi-user environment could be a flocking pain in the rear :-)