rm -f sem ; mkfifo sem

acquire() {
   x='';while test -z "$x"; do read x; done;
}

release() {
   echo '1'
}

job() {
   n=$1; echo "Job $n acquired Semaphore">&2 ; sleep 2; echo "Job $n released Semaphore">&2 ;
}

( acquire < sem ; job 1 ; release > sem ) &
( acquire < sem ; job 2 ; release > sem ) &
( acquire < sem ; job 3 ; release > sem ) &

echo 'Initialize Jobs' >&2 ; echo '1' > sem