If you need to generate a random alpha-numeric string PHP, you can use this simple method:

/**
 * Generate a "random" alpha-numeric string.
 *
 * Should not be considered sufficient for cryptography, etc.
 *
 * @param  int  $length
 * @return string
 */
public static function randomString($length = 16)
{
    $pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

    return substr(str_shuffle(str_repeat($pool, $length)), 0, $length);
}

It was originally used in Laravel PHP framework.