#! /bin/sh
#
# bad lock using touch and file, not atomic

proc() {
  echo "Process $1 begin"
  if [ -r lockfile ]; then # lock already exists
    echo "Process $1 can't lock"
  else # lock did not exist, but another process could get it ahead of us
    touch lockfile # get the lock
    echo "Process $1 got lock"
  fi
  echo "Process $1 end"
}

rm -f lockfile

proc 1 & proc 2 & proc 3 &

wait

rm -f lockfile