Global variables of Drupal 7

Scope can be defined as the range of availability a variable has to the program in which it is declared. PHP variables can be one of four scope types:

1. Local variables
2. Function parameters
3. Global variables
4. Static variables.

Global Variables:

In contrast to local variables, a global variable can be accessed in any part of the program. However, in order to be modified, a global variable must be explicitly declared to be global in the function in which it is to be modified. This is accomplished, conveniently enough, by placing the keyword GLOBAL in front of the variable that should be recognized as global. Placing this keyword in front of an already existing variable tells PHP to use the variable having that name.

Here are the list of Drupal Global Variables:

Name	Description
$base_path	The base path of the Drupal installation.
$base_root	The root URL of the host, excluding the path.
$base_theme_info	An array of objects that represent the base theme.
$base_url	The base URL of the Drupal installation.
$channel	An associative array containing title, link, description and other keys.
$conf	Array of persistent variables stored in 'variable' table.
$cookie_domain	The domain to be used for session cookies.
$databases	Array of database connections.
$element	Structured array describing the data to be rendered.
$forum_topic_list_header	An array of forum topic header information.
$image	Current image tag used by aggregator parsing.
$installed_profile	The name of the profile that has just been installed.
$is_https	Boolean indicating whether or not the current request is secured by HTTPS.
$item	General string or array.
$items	Array of items used by aggregator.
$language	An object containing the information for the active interface language.
$language_content	An object containing the information for the active content language.
$language_url	An object containing the information for the active URL language.
$menu_admin	Boolean indicating that a menu administrator is running a menu access check.
$multibyte	The current multibyte mode.
$pager_limits	Array of the number of items per page for each pager.
$pager_page_array	Array of current page numbers for each pager.
$pager_total	Array of the total number of pages for each pager.
$pager_total_items	Array of the total number of items for each pager.
$tag	Active tag name.
$theme	Name of the active theme.
$theme_engine	The theme engine related to the active theme.
$theme_info	Active theme object.
$theme_key	Name of the active theme.
$theme_path	The path to the active theme.
$timers	Timers that have been created by timer_start().
$update_free_access	Allows the update.php script to be run when not logged in as administrator.
$user	An object representing the user currently visiting the site.