This problem is usually solved by passing a "cookie" to the user with some kind of identifying code or number in it. You'd keep a lookup table of some kind that contained their user information or "session" or whatever else.

I highly recommend CGI::Session for this task. It handles all the mindless tedium for you and provides a familiar API ($session->param("username")) so it drops right into your existing scripts.

I think you might be looking to execute your script with something like LWP or WWW::Mechanize though. You can get this to work, but it'll be a maintenance nightmare in the long run and most likely you'd wish you "did it right in the first place" a few years down the road.