If you're using php compiled as a cgi binary then you can run
php my_job.php "mode=run"
If it's not compiled as a cgi binary you can still use the above and put this at the top of your file.
if (empty($_GET) && !empty($_SERVER['argv'][1])) {
parse_str($_SERVER['argv'][1], $_GET);
}
Or, for that matter, you could just use
php my_job.php run
and in your script do
$mode = $_SERVER['argv'][1];