Mini shell project

Lesson

The shell loop

A shell repeats the same four steps over and over:

1. Read a line of input.
2. Parse that line into argv (an array of argument strings).
3. fork + exec to launch the requested program.
4. wait for that program to finish.

A usable subset fits in about 60 lines of C. "Subset" here means the basics only: no pipes (|) and no redirections (>, <).

Why build one

Writing a mini shell is the classic rite of passage for Linux systems programming. It ties together three core ideas:

• fork — the split into a parent process and a child process.
• exec — replacing the child's program image with a new one.
• wait / exit — the contract by which a parent collects a child's exit status.

Common mistakes

• Not handling EOF (Ctrl-D) on stdin. When input ends, your shell should exit cleanly instead of looping forever.
• Tokenising incorrectly. The argv array you pass to exec must be NULL-terminated, or exec will read past the end of the array.

Practice with these exercises

• Count command arguments
• Count pipeline stages