I had to implement in the cmd.c file the mini-shell. I don't own any of the other files or directories (e.g. tests directory or the grade.sh file).
You need to fork it on a UNIX based operating system and to run the script type ./tests/grade.sh. It will show 90 / 100 (10 points are awarded for coding style, but it needs a docker file which is removed from the repository).
I've spent more than 40 hours on this homework. This was a pretty hard homework. It is very hard to find bugs without proper tools.