function guid(){
    if (function_exists('com_create_guid')){
        return com_create_guid();
    }else{
        mt_srand((double)microtime()*10000);//optional for php 4.2.0 and up.
        $charid = strtoupper(md5(uniqid(rand(), true)));
        $hyphen = chr(45);// "-"
        $uuid = chr(123)// "{"
                .substr($charid, 0, 8).$hyphen
                .substr($charid, 8, 4).$hyphen
                .substr($charid,12, 4).$hyphen
                .substr($charid,16, 4).$hyphen
                .substr($charid,20,12)
                .chr(125);// "}"
        return $uuid;
    }
}
echo guid();

public static function getRandomString($length = 42)
    {
        /*
         * Use OpenSSL (if available)
         */
        if (function_exists('openssl_random_pseudo_bytes')) {
            $bytes = openssl_random_pseudo_bytes($length * 2);

            if ($bytes === false)
                throw new RuntimeException('Unable to generate a random string');

            return substr(str_replace(['/', '+', '='], '', base64_encode($bytes)), 0, $length);
        }

        $pool = '0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ';

        return substr(str_shuffle(str_repeat($pool, 5)), 0, $length);
    }

head /dev/urandom | tr -dc a-z0-9 | head -c 20