Magento -

magento-retrieve-db-info.php

<?php

//  Bootstrap Magento
require_once("../www/app/Mage.php");
$app = Mage::app('default');

//  Grab our database config info
$config = Mage::getConfig()->getResourceConnectionConfig("default_setup");

//  Connect to our RDS MySQL instance
$mysqli = new mysqli($config->host, $config->username, $config->password, $config->dbname);

//  check RDS MySQL connection
if ($mysqli->connect_errno) {
    printf("Connect failed: %s\n", $mysqli->connect_error);
    exit();
}