example config

   if (! defined('ENV')) {
        $URL = strtolower($_SERVER['HTTP_HOST']);

        define('ENV', 'local');
        define('ENV_FULL', 'Local');
        define('ENV_DEBUG', false);
        define('ENV_DOMAIN', $URL);
    }

    $protocol                          = ( isset($_SERVER['HTTPS']) && $_SERVER['HTTPS'] == 'on' ) ? 'https://' : 'http://';
    $base_url                          = $protocol . ENV_DOMAIN;
    $base_path                         = $_SERVER['DOCUMENT_ROOT'];
    $system_folder                     = APPPATH . '../';
    $images_folder                     = 'images';
    $images_path                       = $base_path . '/' . $images_folder;
    $images_url                        = $base_url . '/' . $images_folder;

    $env_config['index_page']          = '';
    $env_config['site_index']          = '';
    $env_config['base_url']            = $base_url . '/';
    $env_config['site_url']            = $env_config['base_url'];
    $env_config['cp_url']              = $env_config['base_url'] . 'admin.php';
    $env_config['theme_folder_path']   = $base_path   . '/themes/';
    $env_config['theme_folder_url']    = $base_url    . '/themes/';
    $env_config['emoticon_path']       = $images_url  . '/smileys/';
    $env_config['emoticon_url']        = $images_url  . '/smileys/';
    $env_config['captcha_path']        = $images_path . '/captchas/';
    $env_config['captcha_url']         = $images_url  . '/captchas/';
    $env_config['avatar_path']         = $images_path . '/avatars/';
    $env_config['avatar_url']          = $images_url  . '/avatars/';
    $env_config['photo_path']          = $images_path . '/member_photos/';
    $env_config['photo_url']           = $images_url  . '/member_photos/';
    $env_config['sig_img_path']        = $images_path . '/signature_attachments/';
    $env_config['sig_img_url']         = $images_url  . '/signature_attachments/';
    $env_config['prv_msg_upload_path'] = $images_path . '/pm_attachments/';

    $env_config['upload_preferences'] = array(
         8 => array(
             'name'        => 'Blog Images',
             'server_path' => $images_path . '/uploads/blog_images/',
             'url'         => $images_url  . '/uploads/blog_images/'
         )
     );



    $config = array_merge($config, $env_config);