#!/usr/bin/env bash
# Limiting number of parallel background tasks

max_jobs=2
running=0

run_task() {
    local item=$1
    printf 'Processing %s\n' "$item"
    sleep 1
}

for item in alpha beta gamma delta; do
    run_task "$item" &
    ((running += 1))

    if [ $running -ge $max_jobs ]; then
        wait -n || {
            printf 'A task failed\n' >&2
            exit 1
        }
        ((running -= 1))
    fi
done

# Wait for remaining tasks
wait
printf 'All tasks finished\n'