Wait for bash background jobs in script to be finished

Question

To maximize CPU usage (I run things on a Debian Lenny in EC2) I have a simple script to launch jobs in parallel:

#!/bin/bash

for i in apache-200901*.log; do         


        

Answer 1

I had to do this recently and ended up with the following solution:

while true; do
  wait -n || {
    code="$?"
    ([[ $code = "127" ]] && exit 0 || exit "$code")
    break
  }
done;

Here's how it works:

wait -n exits as soon as one of the (potentially many) background jobs exits. It always evaluates to true and the loop goes on until:

1. Exit code 127: the last background job successfully exited. In that case, we ignore the exit code and exit the sub-shell with code 0.
2. Any of the background job failed. We just exit the sub-shell with that exit code.

With set -e, this will guarantee that the script will terminate early and pass through the exit code of any failed background job.