I re-implemented lots of basic unix tools. What I would do is go for a command, and just look through OS api references seeing if I could implement it. Once I g

I re-implemented lots of basic unix tools. What I would do is go for a command, and just look through OS api references seeing if I could implement it. Once I got basic functionality, I would go look into the source code and check I did against the standard. I found it super-helpful.