minishell

minishell is a 42 project, built with a partner: a Unix shell in C with lexing, parsing, pipes, redirections, heredocs, signal handling and a set of builtins.

My half was expansion — about 1,400 lines across thirteen files, and the part of a shell that looks trivial until you write it.

echo "hello $NAME" and echo 'hello $NAME' differ by one character, and take different paths through four stages that run in a fixed order: parameter expansion, then field splitting on IFS, then pathname expansion, then quote removal.

The order is the whole subject. Expanding a variable before splitting means a value containing a space becomes two arguments; splitting first means it never can. Removing quotes early would make '$NAME' expand anyway. Each of those is a bug I wrote before I understood why the sequence is what it is.

The version submitted to 42 is the bare project. The repository also carries the unit tests I wrote for the parser and the expansion, which the subject never asked for.

What stayed with me is that the specification was there the entire time — POSIX describes exactly this order — and I still had to hit every case myself before the reasons landed. The standard is not arbitrary. It is a list of decisions somebody already made carefully, and reading it properly would have cost me a week less.