Sounds pretty cool. My biggest problems with xargs is that I had constantly some weird edge cases, so I try to avoid it. As GNU parallel doesn't seem to be part of standard installations it would be an external dependency for a script, which I try to avoid too.

So I ended up using the loop syntax:

  for i in {0..9}; do
    echo "$i" &
  done
  wait

It is not so Unix like, but I find it easier to debug. It would be great if Oil would have a solution for limiting that kind of parallel execution too. I am aware that this isn't simple as there are different options here how to implement it (global limit vs. local limit vs. named limit).

Just an idea from the top of my head an idea for an optional named limit:

Lets call it 'flow':

  flow [options] [command]':
  -n number of max parallel processes
  -c (optional) identifier of the counter.

  Example:

  for i in {0..9}; do
    flow -c myCounter -n 4 echo "$i"
  done

Just an idea.