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Parallel

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Good practices ​

When interrupting the script with ctrl+C, kill the child processes by adding this code at the beginning of the script.

shell
trap 'kill 0' SIGINT

Always add wait after creating child processes.

Simple command ​

Run a command in parallel and get its PID.

shell
command &
pid=$!

Multiple commands ​

shell
{
  echo '[A] Start'
  sleep 10
  echo '[A] Finish'
} &
{
  echo '[B] Start'
  sleep 5
  echo '[B] Finish'
} &

Loop + workers ​

If there are a lot of work to be done in parallel, but you would like to have a limited amount of workers, something like this might work (not tested):

shell
for ...; do
  if [[ $(jobs -p | wc -l) -ge 4 ]]; then
    wait -n
  fi
  do_stuff &
done