Trying to remember all the passwords is the killer here. If you really want to do it in some random way instead of in a more ordered way, why not pick the first three characters at random, and then try all combinations of the next two characters? Of course, that still doesn't scale, and will probably break down after 6 characters.

Note also that in real life, the allowable set of characters is much more than the set you are using, making you run out of memory even faster.

You may want a much smarter datastructure, for instance based on a trie and bitvectors as leaves to keep track of the tried passwords. It'll take more work (codewise) to insert and search, but you'll save on memory.

I wouldn't even dream to use Perl for any such brute force work. This seems like a job for C. Specially since if you're going to use anything like this in practise, you only have the encrypted password.