- print_r: documentation ( source)
- usort: documentation ( source)
<?php
$arr=array("aa", "az", "an","am", "ba", "by", "alien","i");
usort($arr, function ($a, $b) {
return strlen($a) == strlen($b) ? $a <=> $b : strlen($a) <=> strlen($b);
});
print_r($arr);