This shell script checks if process exists and removes pid file if not. I use this script with monit to be sure that process exist before killing it

check_pid_valid.sh

#!/usr/bin/env bash
# the first argument should be a path to pid file
if [[ -f "$1" ]] ; then
  if [ $(ps -p $(cat $1) | wc -l) -gt 1 ] ; then
    # process exists - do nothing
    #echo "OK"
    exit 0
  else
    #echo "will do rm $1"
    rm $1
  fi
fi