PHP Superglobals

Introduction

In PHP, superglobal variables are special variables that are predefined and accessible from anywhere within a PHP script. They hold information about the server, client, and environment, allowing developers to access and manipulate important data without having to explicitly pass them as parameters or retrieve them from external sources. Superglobals are available in all scopes of a PHP script, including functions, classes, and global scope.

Superglobal variables are denoted with a leading underscore followed by uppercase letters, such as $_SERVER, $_GET, $_POST, $_SESSION, and more. Each superglobal variable serves a specific purpose and provides different types of information. For example, $_SERVER contains information about the server and execution environment, including request headers, server details, and paths. $_GET and $_POST store data submitted through HTTP GET and POST methods, respectively.

Superglobal variables are useful in various scenarios, such as accessing form data, managing user sessions, retrieving server information, handling cookies, and more. However, it is important to handle superglobal variables with caution, as they directly expose data from external sources. Proper input validation, sanitization, and security measures should be implemented to prevent potential security vulnerabilities, such as SQL injection and cross-site scripting (XSS) attacks.

List of Superglobal Variables Available in PHP

Superglobal variables in PHP are special variables that are available in all scopes throughout the script. They are predefined by PHP and provide essential information and functionality. Here is a list of the most commonly used superglobal variables in PHP:

• $_GLOBALS : It is an associative array that contains references to all global variables in PHP. It can be accessed from within any scope, allowing you to access global variables without using the global keyword.

• $_SERVER : It is an array that provides information about the server and the execution environment. It contains various server-related details such as server name, request method, script filename, and more.

• $_GET : It is an associative array that holds the values of the query string parameters passed in the URL. It is commonly used to retrieve data from the URL in HTTP GET requests.

• $_POST: It is an associative array that contains the values of variables sent to the current script via an HTTP POST request. It is typically used to handle form submissions and process user input.

• $_FILES : It is an associative array that provides information about uploaded files in an HTTP POST request. It contains details such as file name, file type, temporary file location, etc.

• $_COOKIE : It is an associative array that holds the values of cookies sent by the client to the server. Cookies are used to store small amounts of data on the client side.

• $_SESSION : It is an associative array that stores and retrieves session-specific data across multiple requests. It allows you to persist data between different pages or interactions with a user.

• $_REQUEST : It is a combination of $_GET, $_POST, and $_COOKIE superglobal arrays. It contains the values passed through any HTTP request method (GET, POST, or COOKIE). However, it is generally recommended to access the specific superglobal arrays ($_GET,$_POST, or $_COOKIE) directly.

• $_ENV : It is an associative array that provides access to the environment variables set on the server. Environment variables contain system-specific information such as the server's operating system, paths, and configuration settings.

• $_SERVER : As mentioned earlier, it is an array that contains various server-related information. It includes details like HTTP headers, server IP address, request method, server software, and more.

• $_SESSION: It is an associative array used to store session data. It allows you to create, retrieve, update, and destroy session variables.

These superglobal variables offer convenient access to crucial information and facilitate communication and data handling between different parts of a PHP script. They simplify common tasks such as accessing form data, working with cookies, managing sessions, and interacting with the server environment. Understanding and utilizing these superglobals effectively can enhance the functionality and flexibility of your PHP applications.

Examples

Accessing Form Data:

Explanation

In this example, you have an HTML form with input fields for the username and password. When the form is submitted, the data is sent to the process.php file. In process.php, you can access the form data using the $_POST superglobal variable. It is an associative array that contains key-value pairs, where the keys are the names of the form inputs. So, $_POST['username'] retrieves the value entered in the username field, and $_POST['password'] retrieves the value entered in the password field. Run the above code in your editor for a better and clear explanation.

Retrieving Query Parameters:

Explanation

When you have a URL with query parameters, such as example.com/page.php?id=123, you can retrieve the value of the id parameter using the $_GET superglobal variable. It is also an associative array that contains the query parameters as key-value pairs. So, $_GET['id'] retrieves the value 123. You can use this to customize the behaviour of your PHP script based on the provided parameters. Run the above code in your editor for a better and clear explanation.

Working with Cookies:

Explanation

Cookies are small pieces of data stored on the user's computer. PHP provides the $_COOKIE superglobal variable to access and manipulate cookie data. If you have a cookie named "username", you can retrieve its value using $_COOKIE['username']. This allows you to personalize the user experience or remember certain preferences by storing data on the user's computer. Run the above code in your editor for a better and clear explanation.

Storing Session Data:

Explanation

Sessions allow you to store user-specific data that persists across multiple page requests. PHP provides the $_SESSION superglobal variable for this purpose. You can assign values to specific session keys, like $_SESSION['username'] = 'John', to store information. Later, you can retrieve the value using $_SESSION['username']. Sessions are useful for maintaining user login status, storing shopping cart contents, or storing temporary data during a user's visit. Run the above code in your editor for a better and clear explanation.

Uploading Files:

When handling file uploads, the $_FILES superglobal variable provides information about the uploaded file(s). For example, if you have a file input with the name "avatar":

Explanation

When dealing with file uploads, PHP provides the $_FILES superglobal variable to handle the uploaded files. It contains information about the uploaded file(s) such as the file name, size, temporary location, and more. For example, if you have a file input with the name "avatar", you can access the uploaded file's properties using $_FILES['avatar']. This allows you to process and save the uploaded file on the server. Run the above code in your editor for a better and clear explanation.