How to force a PHP command line script to run in a single process_PHP Tutorial

   if (!empty($last_pid))
   {
    $command = exec("/bin/ps -p $last_pid -o command=");

    if ($command == $processName)
    {
     return false;
    }
   }
  }

  $cur_pid = posix_getpid();

  if ($fp = @fopen($pidFile, "wb"))
  {
   fputs($fp, $cur_pid);
   ftruncate($fp, strlen($cur_pid));
   fclose($fp);

   return true;
  }
  else
  {
   return false;
  }
 }

 /**
* Get the Command
corresponding to the current process *
* @return string command and its parameters
*/
 function getCurrentCommand()
 {
  $pid     = posix_getpid();
  $command = exec("/bin/ps -p $pid -o command=");

  return $command;
 }