limit shellscript process to only one 1 process, to prevent running twice

singleprocess.bash

# forces/limits shellscript to only one 1 process, to prevent running twice, aka bash singleton
# this function exits when no parameter is passed, and another instance of the script is detected
# @dependancies ps grep tr sed
# @param string (pass --kill to kill previous process)
# usage: change 'foo' and 'bar' to the strings which occur in your process name

function singleprocess(){
  PID=$$;                            # current process
  if [[ "$1" == "--kill" ]]; then 
    PID="$(ps aux | grep foo | grep bar | tr -s [:space:] | cut -d' ' -f2 )"
    [[ $? == 0 ]] && [[ ${#PID} != 0 ]] && echo "killing previous pid $PID" && kill -9 $PID 
  else
    ps aux | grep "$(basename $0)" | grep -v grep | grep -v $PID &>/dev/null && exit 0; # dont run twice
  fi
}