My Perl experience only goes back as far as 5.6.1, you'll need merlyn or one of the others with the Knowledge of the Ancients (sorry, too much Stargate :), for the answer to your question. I pretty sure that P4 had hashes, but I don;t even know when that came into being.

I do know that REXX had associative arrays way back in 1987. That was my first encounter with them, and I remember thinking that the were bloody nearly magical before I read up on hashing and hashing algorithms.