- print_r: documentation ( source)
- array_diff: documentation ( source)
<?php
$array1 = array('red', 'blue', 'green', 'octarine');
$array2 = array('red', 'yellow', 'green');
$diff = array_diff($array1, $array2);
print_r($diff); //Array ( [1] => blue [3] => octarine )