随机串

function random($length, $chars = '0123456789') {
    $hash = '';
    $max = strlen($chars) - 1;
    for($i = 0; $i < $length; $i++) {
        $hash .= $chars[mt_rand(0, $max)];
    }
    return $hash;
}

var_dump(random(6, '123456789abcdefghijklmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ'));