How can I implement my own basic unix shell in C?

Question

I\'m a newbie to process and thread management. My Shell should understand PATH environment variable. It can be set and modified. It runs in two ways -interacti

Answer 1

Your main loop is:

• read a line (use fgets(3) for a simple shell, readline(3) for a fancy one)
• parse the command
• fork and execute the pipelines

To parse the command, there are two common choices. Write a recursive descent parser or use yacc(1) to generate one. It's a lot easier to bang out an initial parser using yacc, but you can totally get stuck debugging it and it really wants to be context-free. I prefer recursive descent but just about everyone else in the world prefers using yacc. (Technically, bison.) If the shell is really really simple, like a homework shell, yacc may be overkill.

To do the lexical analysis you can also roll your own or use flex.

You won't need to use any threads.