How to create cron job using PHP

Question

 I want to create a cron job that will execute my code every minute. I'm using PHP to create it. It is not working.

Example

run.php This is the code that executes every minute:

<?php

echo "This code will run every minute";

?>

cron.php

<?php

$path = dirname(__FILE__);
$cron = $path . "/run.php";
echo exec("***** php -q ".$cron." &> /dev/null");

?>

Can someone please help me with this?