Generate unique strings. Tested over 100.000.000 iterations without duplicates.

uniqid.php

<?php declare(strict_types=1);

if (!function_exists('uniqidReal')) {
    /**
     * @param int $length
     *
     * @return string
     */
    function uniqidReal(int $length): string
    {
        $string = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

        return substr(str_shuffle(str_repeat($string, rand(2, 5))), 0, $length);
    }
}

z-test.php

<?php declare(strict_types=1);

ini_set('memory_limit', '-1');
set_time_limit(0);

$limit = 100000000;
$list = [];

for ($i = 0; $i < $limit; $i++) {
    $id = uniqidReal(10);

    if (isset($list[$id])) {
        die($id.' found on position '.number_format($i));
    }

    $list[$id] = true;
}

die('Repeated ids not generated');