$_REQUEST

$_GET

$_POST

$_COOKIE

$_SESSION

$_SERVER

$_SERVER is an array containing information such as headers, paths, and script locations. The entries in this array are created by the webserver. This variable is a superglobal, or automatic global, variable. This simply means that it is available in all scopes throughout a PHP program. You don't need to do declare it as global $_SERVER;.

There is no guarantee that every web server will provide any of these; servers may omit some, or provide others not listed here. You may or may not find any of the following elements in $_SERVER:

1. 'PHP_SELF'. The filename of the currently executing script, relative to the document root.
2. 'argv'. Array of arguments passed to the script.
3. 'argc'. Contains the number of command line parameters passed to the script (if run on the command line).
4. 'GATEWAY_INTERFACE'. What revision of the CGI specification the server is using; i.e. 'CGI/1.1'.
5. 'SERVER_ADDR'. The IP address of the server under which the current script is executing.
6. '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.

1. 'SERVER_SOFTWARE'. Server identification string, given in the headers when responding to requests.
2. 'SERVER_PROTOCOL'. Name and revision of the information protocol via which the page was requested i.e. 'HTTP/1.0';
3. 'REQUEST_METHOD'. Which request method was used to access the page; i.e. 'GET', 'HEAD', 'POST', 'PUT'.
4. 'REQUEST_TIME'. The timestamp of the start of the request. Available since PHP 5.1.0.
5. 'QUERY_STRING'. The query string, if any, via which the page was accessed.
6. 'DOCUMENT_ROOT'. The document root directory under which the current script is executing, as defined in the server's configuration file.
7. 'HTTP_ACCEPT'. Contents of the Accept: header from the current request, if there is one.
8. 'HTTP_ACCEPT_CHARSET'. Contents of the Accept-Charset: header from the current request, if there is one. Example: iso-8859-1, *, utf-8.
9. 'HTTP_ACCEPT_ENCODING'. Contents of the Accept-Encoding: header from the current request, if there is one.
10. 'HTTP_ACCEPT_LANGUAGE'. Contents of the Accept-Language: header from the current request, if there is one.
11. 'HTTP_CONNECTION'. Contents of the Connection: header from the current request, if there is one.
12. 'HTTP_HOST'. Contents of the Host: header from the current request, if there is one.
13. 'HTTP_REFERER'. The address of the page (if any) which referred the user agent to the current page.
14. 'HTTP_USER_AGENT'. Contents of the User-Agent: header from the current request, if there is one. This is a string denoting the user agent being which is accessing the page.
15. 'HTTPS'. Set to a non-empty value if the script was queried through the HTTPS protocol.
16. 'REMOTE_ADDR'. The IP address from which the user is viewing the current page.
17. 'REMOTE_HOST'. The Host name from which the user is viewing the current page. The reverse dns lookup is

based off the REMOTE_ADDR of the user. Your web server must be configured to create this variable. For example in Apache you'll need HostnameLookups=On inside httpd.conf for it to exist.

1. 'REMOTE_PORT'. The port being used on the user's machine to communicate with the web server.
2. 'SCRIPT_FILENAME'. The absolute pathname of the currently executing script.
3. '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.

1. '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.
2. 'SERVER_SIGNATURE'. String containing the server version and virtual host name which are added to server generated pages, if enabled.
3. 'SCRIPT_NAME'. Contains the current script's path.
4. 'REQUEST_URI'. The URI which was given in order to access this page; for instance, /index.html.
5. 'PHP_AUTH_DIGEST'. When running under Apache as module doing Digest HTTP authentication this variable

is set to the 'Authorization' header sent by the client (which you should then use to make the appropriate validation).

1. 'PHP_AUTH_USER'. When running under Apache or IIS (ISAPI on PHP 5) as module doing HTTP authentication this variable is set to the username provided by the user.
2. 'PHP_AUTH_PW'. When running under Apache or IIS (ISAPI on PHP 5) as module doing HTTP authentication this variable is set to the password provided by the user.
3. 'AUTH_TYPE'. When running under Apache as module doing HTTP authenticated this variable is set to the authentication type.