Super global variables were enabled after PHP 4.1.0. They are variables that come with the PHP system and are available in the entire scope of a script.
Several superglobals are predefined in PHP, which means that they are available in the entire scope of a script. You can use it in functions and classes without special instructions.
List of PHP super global variables:
$GLOBALS
$_SERVER
$_REQUEST
$_POST
$_GET
$_FILES
$_ENV
$_COOKIE
$_SESSION
In this chapter we will explain several commonly used super global variables, and we will introduce the remaining variables in the next few chapters.
$GLOBALS is a super global variable group in PHP that can be accessed in the entire scope of a PHP script.
$GLOBALS is a global combined array containing all variables. The name of the variable is the key of the array.
The following example shows how to use the super global variable $GLOBALS:
<?php $x = 75 ; $y = 25 ; function addition ( ) { $GLOBALS [ ' z ' ] = $GLOBALS [ ' x ' ] + $GLOBALS [ ' y ' ] ; } addition ( ) ; echo $z ; ?>
In the above example, z is a super global variable in the $GLOBALS array, which can also be accessed outside the function.
$_SERVER is an array containing information such as header, path, and script locations. The items in this array are created by the web server. There is no guarantee that every server will offer all items; servers may ignore some, or serve items not listed here.
The following example shows how to use elements in $_SERVER:
<?php echo $_SERVER [ ' PHP_SELF ' ] ; echo " <br> " ; echo $_SERVER [ ' SERVER_NAME ' ] ; echo " <br> " ; echo $_SERVER [ ' HTTP_HOST ' ] ; echo " <br> " ; echo $_SERVER [ ' HTTP_REFERER ' ] ; echo " <br> " ; echo $_SERVER [ ' HTTP_USER_AGENT ' ] ; echo " <br> " ; echo $_SERVER [ ' SCRIPT_NAME ' ] ; ?>
The following table lists the important elements in all $_SERVER variables:
| element/code | describe |
|---|---|
| $_SERVER['PHP_SELF'] | The file name of the currently executing script, related to document root. For example, using $_SERVER['PHP_SELF'] in a script at http://example.com/test.php/foo.bar will result in /test.php/foo.bar. The __FILE__ constant contains the full path and filename of the current (i.e. containing) file. Starting with PHP version 4.3.0, this variable will contain the script name if PHP is running in command line mode. This variable is not available in previous versions. |
| $_SERVER['GATEWAY_INTERFACE'] | The version of the CGI specification used by the server; for example, "CGI/1.1". |
| $_SERVER['SERVER_ADDR'] | The IP address of the server where the script is currently running. |
| $_SERVER['SERVER_NAME'] | The hostname of the server where the script is currently running. If the script is running on a virtual host, the name is determined by the value set for that virtual host. (eg: www.codercto.com) |
| $_SERVER['SERVER_SOFTWARE'] | Server identification string, given in the header information when responding to the request. (eg: Apache/2.2.24) |
| $_SERVER['SERVER_PROTOCOL'] | The name and version of the communication protocol used when requesting the page. For example, "HTTP/1.0". |
| $_SERVER['REQUEST_METHOD'] | The request method used to access the page; for example, "GET", "HEAD", "POST", "PUT". |
| $_SERVER['REQUEST_TIME'] | The timestamp when the request started. Available since PHP 5.1.0. (eg: 1377687496) |
| $_SERVER['QUERY_STRING'] | query string (query string), if any, through which page access is performed. |
| $_SERVER['HTTP_ACCEPT'] | The content of the Accept: item in the current request header, if it exists. |
| $_SERVER['HTTP_ACCEPT_CHARSET'] | The content of the Accept-Charset: item in the current request header, if it exists. For example: "iso-8859-1,*,utf-8". |
| $_SERVER['HTTP_HOST'] | The contents of the Host: field in the current request header, if present. |
| $_SERVER['HTTP_REFERER'] | Directs the user agent to the address of the page preceding the current page, if one exists. Determined by user agent settings. Not all user agents will set this item, and some also provide the function of modifying HTTP_REFERER. In short, the value is not trustworthy. ) |
| $_SERVER['HTTPS'] | Set to a non-empty value if the script is accessed via the HTTPS protocol. |
| $_SERVER['REMOTE_ADDR'] | The IP address of the user viewing the current page. |
| $_SERVER['REMOTE_HOST'] | The hostname of the user browsing the current page. DNS reverse resolution does not depend on the user's REMOTE_ADDR. |
| $_SERVER['REMOTE_PORT'] | The port number used on the user's machine to connect to the web server. |
| $_SERVER['SCRIPT_FILENAME'] | The absolute path of the currently executing script. |
| $_SERVER['SERVER_ADMIN'] | This value specifies the SERVER_ADMIN parameter in the Apache server configuration file. If the script is running on a virtual host, this value is that of that virtual host. (eg: [email protected]) |
| $_SERVER['SERVER_PORT'] | The port used by the web server. The default value is "80". If using SSL secure connection, this value is the HTTP port set by the user. |
| $_SERVER['SERVER_SIGNATURE'] | A string containing the server version and virtual hostname. |
| $_SERVER['PATH_TRANSLATED'] | The base path of the file system (not the document root) where the current script is located. This is the result after the server has been imaged from a virtual to real path. |
| $_SERVER['SCRIPT_NAME'] | Contains the path to the current script. This is useful when the page needs to point to itself. The __FILE__ constant contains the full path and file name of the current script (such as an include file). |
| $_SERVER['SCRIPT_URI'] | URI is used to specify the page to be accessed. For example "/index.html". |
PHP $_REQUEST is used to collect data submitted by HTML forms.
The following example shows a form with input fields and submit buttons. When the user submits form data by clicking the "Submit" button, the form data will be sent to the script file specified in the action attribute of the <form> tag. In this example, we specify the file to handle the form data. If you want another PHP file to handle this data, you can modify the specified script file name. Then, we can use the super global variable $_REQUEST to collect input field data in the form:
<html><body><form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">Name: <input type="text" name="fname"><input type ="submit"></form><?php $name = $_REQUEST['fname']; echo $name; ?></body></html>
PHP $_POST is widely used to collect form data. Specify this attribute in the HTML form tag: "method="post".
The following example shows a form with input fields and submit buttons. When the user submits form data by clicking the "Submit" button, the form data will be sent to the script file specified in the action attribute of the <form> tag. In this example, we specify the file to handle the form data. If you want another PHP file to handle this data, you can modify the specified script file name. Then, we can use the super global variable $_POST to collect the input field data in the form:
<html><body><form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">Name: <input type="text" name="fname"><input type ="submit"></form><?php $name = $_POST['fname']; echo $name; ?></body></html>
PHP $_GET is also widely used to collect form data. Specify this attribute in the HTML form tag: "method="get".
$_GET can also collect data sent in the URL.
Assume we have a hyperlinked HTML page containing parameters:
<html><body><a href="test_get.php?subject=PHP&web=codercto.com">Test $GET</a></body></html>
When the user clicks on the link "Test $GET", the parameters "subject" and "web" will be sent to "test_get.php". You can use the $_GET variable in the "test_get.php" file to get this data.
The following example shows the code of the "test_get.php" file:
<html><body><?php echo "Study " . $_GET['subject'] . " at " . $_GET['web'];?></body></html>
Tip: If you want to learn more about $_POST and $_GET, visit our PHP Forms chapter.