fork() a background task

[HighSeraphim]

I am building a small shell for school. I have the forground tasks handled with fork(), execvp() and waitpid().

Now I need to handle background tasks. I'm handling parsing out the & at the end.

I need to know how to send the child to the background

AND

how to set up an asynchronous waitpid() so that I know when the task completes. (I have to print usage information which I believe I can process the same way as my foreground tasks.


Thanks!

[brewbuck]

I need to know how to send the child to the background

Note that "foreground" and "background" are shell concepts, and have nothing to do with the OS itself. How you send a process to the background is completely up to you.

The real difference between a foreground process and a background process is that for a foreground process, the shell calls wait() to wait for the child to finish. For a background process, simply don't do that.

When a child process dies, your shell will receive a SIGCHLD signal. You can install a signal handler for this signal, and call wait() from within this handler to reap the dead child (actually, you want to call wait() in a loop until no more processes can be reaped, since more than one child might have died). Beyond that, it's fire-and-forget. Fork off the child just like any other process, then go about your business.