spawn is a simple parallel execution utility written to appeal to the Unix mindset.

spawn reads shell command lines from stdin, one per line, and then executes them as maximum of N child processes in parallel, and waits for all of the children to exit.

If a child process fails with a non-zero exit code, no new children are spawned. Then spawn waits for all existing children to exit and returns the failed exit code.

I wrote ``spawn'' to scratch my own itch because I didn't find anything simple and purposeful to do the job.