The classic for 'program vs. program' is robot programming. This can be aibots (Perl engine, proprietary robot command language) or http://realtimebattle.sourceforge.net/ (Unix, message based communication via pipes, agnostic to programming languages).

A fun way to introduce and evolutionize concepts: E. g. students will develop a maze of 'if' statements; you introduce state machines.

Becoming off-topic I'd not teach the language but problem solving, common algorithms and concepts. Perl has a lot of algorithm per line of code, reducing distraction.