If this interests somebody, then I suggest they'd read "The Unix Programming Environment" By B.W Kernighan, and Rob. Pike. It gives you the concepts, and learns you tools like yacc, that lets you off a lot of tedious tasks when writing an interpreter of sorts. Then follow up with at least "Advanced Unix Programming" By Stevens.

The universe of commandline tools is still not completed, and this kind of programming is fun! fun! fun!

Personally I miss the Plan-9's plumb utility. :)