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# Predefined variables

PHP provides a large number of predefined variables to any script which it runs. Many of these variables, however, cannot be fully documented as they are dependent upon which server is running, the version and setup of the server, and other factors. Some of these variables will not be available when PHP is run on the command-line.

Despite these factors, here is a list of predefined variables available under a stock installation of PHP 3 running as a module under a stock installation of Apache 1.3.6.

For a list of all predefined variables (and lots of other useful information), please see (and use) phpinfo().

> Note: This list is neither exhaustive nor intended to be. It is simply a guideline as to what sorts of predefined variables you can expect to have access to in your script.

## Apache variables

These variables are created by the Apache webserver. If you are running another webserver, there is no guarantee that it will provide the same variables; it may omit some, or provide others not listed here. That said, a large number of these variables are accounted for in the CGI 1.1 specification, so you should be able to expect those.

Note that few, if any, of these will be available (or indeed have any meaning) if running PHP on the command line.

$GATEWAY_INTERFACE

  What revision of the CGI specification the server is using; i.e. 'CGI/1.1'.

$SERVER_NAME

  The name of the server host under which the current script is executing. If the script is running on a virtual host, this will be the value defined for that virtual host.

$SERVER_SOFTWARE

  Server identification string, given in the headers when responding to requests.

$SERVER_PROTOCOL

  Name and revision of the information protocol via which the page was requested; i.e. 'HTTP/1.0';

$REQUEST_METHOD

  Which request method was used to access the page; i.e. 'GET', 'HEAD', 'POST', 'PUT'.

$QUERY_STRING

  The query string, if any, via which the page was accessed.

$DOCUMENT_ROOT

  The document root directory under which the current script is executing, as defined in the server's configuration file.

$HTTP_ACCEPT

  Contents of the `Accept:` header from the current request, if there is one.

$HTTP_ACCEPT_CHARSET

  Contents of the `Accept-Charset:` header from the current request, if there is one. Example: 'iso-8859-1,*,utf-8'.

$HTTP_ACCEPT_ENCODING

  Contents of the `Accept-Encoding:` header from the current request, if there is one. Example: 'gzip'.

$HTTP_ACCEPT_LANGUAGE

  Contents of the `Accept-Language:` header from the current request, if there is one. Example: 'en'.

$HTTP_CONNECTION

  Contents of the `Connection:` header from the current request, if there is one. Example: 'Keep-Alive'.

$HTTP_HOST

  Contents of the `Host:` header from the current request, if there is one.

$HTTP_REFERER

  The address of the page (if any) which referred the browser to the current page. This is set by the user's browser; not all browsers will set this.

$HTTP_USER_AGENT

  Contents of the `User_Agent:` header from the current request, if there is one. This is a string denoting the browser software being used to view the current page; i.e. `Mozilla/4.5 [en] (X11; U; Linux 2.2.9 i586)`. Among other things, you can use this value with get_browser() to tailor your page's functionality to the capabilities of the user's browser.

$REMOTE_ADDR

  The IP address from which the user is viewing the current page.

$REMOTE_PORT

  The port being used on the user's machine to communicate with the web server.

$SCRIPT_FILENAME

  The absolute pathname of the currently executing script.

$SERVER_ADMIN

  The value given to the SERVER_ADMIN (for Apache) directive in the web server configuration file. If the script is running on a virtual host, this will be the value defined for that virtual host.

$SERVER_PORT

  The port on the server machine being used by the web server for communication. For default setups, this will be '80'; using SSL, for instance, will change this to whatever your defined secure HTTP port is.

$SERVER_SIGNATURE

  String containing the server version and virtual host name which are added to server-generated pages, if enabled.

$PATH_TRANSLATED

  Filesystem- (not document root-) based path to the current script, after the server has done any virtual-to-real mapping.

$SCRIPT_NAME

  Contains the current script's path. This is useful for pages which need to point to themselves.

$REQUEST_URI

  The URI which was given in order to access this page; for instance, '/index.html'.

## Environment variables

These variables are imported into PHP's global namespace from the environment under which the PHP parser is running. Many are provided by the shell under which PHP is running and different systems are likely running different kinds of shells, a definitive list is impossible. Please see your shell's documentation for a list of defined environment variables.

Other environment variables include the CGI variables, placed there regardless of whether PHP is running as a server module or CGI processor.

## PHP variables

These variables are created by PHP itself. The `$HTTP_*_VARS` variables are available only if the track_vars configuration is turned on. When enabled, the variables are always set, even if they are empty arrays. This prevents a malicious user from spoofing these variables.

> Note: As of PHP 4.0.3, track_vars is always turned on, regardless of the configuration file setting.

If the register_globals directive is set, then these variables will also be made available in the global scope of the script; i.e., separate from the `$HTTP_*_VARS` arrays. This feature should be used with care, and turned off if possible; while the `$HTTP_*_VARS` variables are safe, the bare global equivalents can be overwritten by user input, with possibly malicious intent. If you cannot turn off register_globals, you must take whatever steps are necessary to ensure that the data you are using is safe.

$argv

  Array of arguments passed to the script. When the script is run on the command line, this gives C-style access to the command line parameters. When called via the GET method, this will contain the query string.

$argc

  Contains the number of command line parameters passed to the script (if run on the command line).

$PHP_SELF

  The filename of the currently executing script, relative to the document root. If PHP is running as a command-line processor, this variable is not available.

$HTTP_COOKIE_VARS

  An associative array of variables passed to the current script via HTTP cookies.

$HTTP_GET_VARS

  An associative array of variables passed to the current script via the HTTP GET method.

$HTTP_POST_VARS

  An associative array of variables passed to the current script via the HTTP POST method.

$HTTP_POST_FILES

  An associative array of variables containing information about files uploaded via the HTTP POST method. See POST method uploads for information on the contents of `$HTTP_POST_FILES`.

  `$HTTP_POST_FILES` is available only in PHP 4.0.0 and later.

$HTTP_ENV_VARS

  An associative array of variables passed to the current script via the parent environment.

$HTTP_SERVER_VARS

  An associative array of variables passed to the current script from the HTTP server. These variables are analogous to the Apache variables described above.

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