Bash Challenge #1 Solution

bash-challenge-1-solution.sh

#!/bin/bash

if [[ -z $1 ]]; then
  echo "Usage: $(basename $0) NUM_PROCESSES COMMAND..."
fi

NUM_PROCESSES=$1
shift

SEMAPHORE=/tmp/semaphore.$RANDOM
exec 3<>${SEMAPHORE}

function up() {
  echo ready >> ${SEMAPHORE}
}

function down() {
  local token=
  while [[ $token != "ready" ]]; do
    read token <&3 || sleep 1
  done
}

i=$NUM_PROCESSES
while (( i-- )); do
  up
done

cat ${SEMAPHORE}

for command in "$@"; do
  (down && eval "$command"; up) &
done

wait