php生成随机数

/**
 * 生成随机数
 * @param int $length
 * @return string
 */
function random_keys($length)
{
    $pattern = array(
        '1','2','3','4','5','6','7','8','9','0',
        'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z',
        'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'
    );
    $keys = array_rand($pattern, $length);
    $key = '';
    for ($i = 0; $i < $length; $i++) {
        $key .= $pattern[$keys[$i]];    //生成php随机数
    }
    return $key;
}