It sound like you're trying to take a file from the user's drive, upload it and then do something interesting with it.

If you look through CGI's POD, you'll come across a section called "Creating a file upload field". It describes the process of adding fields to a form to let users send your script files. It uploads the file and provides a filehandle automatically for your enjoyment.
There's not much to add to Stein's documentation, really, it's pretty cookbook like.