Cloning basic *nix commands is a good excercise. cat, ls, od, md5sum, grep are all simple one/two day jobs for a newbie. He'll have the functional specifications on his system in the man pages, the source in another language, and it will teach him how to deal with IO, stdin/stdout/stderr, subroutines....

It sounds like he's a wannabe. Work with that. What does he want to do? I've taught a few people scripting languages over the years, and it goes a lot faster when they're making something they need.