Named Capturing Group REGEX

named_groups_regex.php

<?php

$regex = "/(?'group1'[0-9]+)_(?'group2'.+)_(?'group3'[0-9A-Z]+).(?'ext'.+)$/";

$files = [
    '01_lero_1X.pdf',
    '02_lerolero_13.pdf',
    '03_1k_KK.pdf'
];

foreach ($files as $key => $name) {
    preg_match($regex, $name, $matches);
    print_r($matches);
}