Question

I implemented a simple c shell to take in commands like sleep 3 &. I also implemented it to “listen” for sigchild signals once the job complete.

But how do I get the job id and command to be printed out like the ubuntu shell once it is completed?

Answer 1

I would advise against catching SIGCHLD signals.

A neater way to do that is to call waitpid with the WNOHANG option. If it returns 0, you know that the job with that particular pid is still running, otherwise that process has terminated and you fetch its exit code from the status parameter, and print the message accordingly.

Moreover, bash doesn’t print the job completion status at the time the job completes, but rather at the time when the next command is issued, so this is a perfect fit for waitpid.

A small disadvantage of that approach is that the job process will stay as a zombie in the period between its termination and the time you call waitpid, but that probably shouldn’t matter for a shell.