I'm a php person, so I can't offer code, but I do understand the question which is being asked.

Rather than showing a url of /?a=123456, the questioner is looking for a url that says /?a=rqz instead. By using the full range of alphanumeric characters, he is hoping to reduce the MD5 from a 32 character string (using 0-9,a-f), into something much smaller, maybe a 12 character string (using 0-9, a-z). This has the benefit of being shorter, while still spanning the same range of values (2^32) as MD5.

php has the function: string base_convert (string number, int frombase, int tobase), which I'm sure has an equivalent in perl. Once you find this function the problem is reduced to:

$new_number = base_convert( md5('whatever'), 16, 36 ); // 10 digits + 26 alphanumeric

Hopefully some perl guru will be able to point you in the right direction.

--Robert