Run Bash subshells in parallel

parallel-subshells.sh

#!/bin/bash

TMP_DIR="$(mktemp -d -t subshells.XXXXXXXXXX)"
function cleanup {
    rm -rf "${TMP_DIR}"
}
trap cleanup EXIT

PIDS=()
for i in 1 2 3; do
  (
    echo "$(date)" >> "${TMP_DIR}/${BASHPID}.out"
  ) &
  PID="$!"
  PIDS+=("${PID}")
  echo "$$ started ${PID}"
done

for PID in ${PIDS[@]}; do
  wait ${PID}
  cat "${TMP_DIR}/${PID}.out"
done