Overriding $base_url in Drupal 7

settings-base_url.php

<?php

/**
 * Base URL (optional).
 *
 * If Drupal is generating incorrect URLs on your site, which could
 * be in HTML headers (links to CSS and JS files) or visible links on pages
 * (such as in menus), uncomment the Base URL statement below (remove the
 * leading hash sign) and fill in the absolute URL to your Drupal installation.
 *
 * You might also want to force users to use a given domain.
 * See the .htaccess file for more information.
 *
 * Examples:
 *   $base_url = 'http://www.example.com';
 *   $base_url = 'http://www.example.com:8888';
 *   $base_url = 'http://www.example.com/drupal';
 *   $base_url = 'https://www.example.com:8888/drupal';
 *
 * It is not allowed to have a trailing slash; Drupal will add it
 * for you.
 */
$base_url = 'http://www.example.com';  // NO trailing slash!