PHP Superglobals

PHP superglobals are predefined variables that are globally available in all scopes. They are used to handle different types of data, such as input data, server data, session data, and more. These superglobal arrays allow developers to easily work with these global data structures without the need to declare them globally.

List of PHP Superglobals

Here is a list of the most commonly used PHP superglobals:

1. $GLOBALS
2. $_SERVER
3. $_REQUEST
4. $_GET
5. $_POST
6. $_SESSION
7. $_COOKIE
8. $_FILES
9. $_ENV

Let us now learn about some of these superglobals in detail:  

1. $_GET - Get Data from URL Query Parameters

The $_GET Superglobal is used to collect form data after submitting a form with the GET method. It is also used to retrieve data from the query string of the URL. When a form is submitted using the GET method, the data is sent as URL parameters.

Now, let us understand with the help of the example:

// URL: index.php?name=anjali&age=23

<?php
echo "Name: " . $_GET['name'];  
echo "Age: " . $_GET['age'];    
?>

In this case, $_GET['name'] retrieves the value of name from the URL.

Important Notes:

• $_GET is not secure for transmitting sensitive data as the data is visible in the URL.
• It has a limit on the amount of data that can be sent due to URL length limitations.

2. $_POST - Post Data from Forms

The $_POST superglobal is used to collect form data after submitting a form with the POST method. This method is more secure than GET as the data is sent in the body of the HTTP request, not in the URL. When a user submits a form with sensitive data (e.g., passwords), it is recommended to use POST as it does not expose data in the URL.

Now, let us understand with the help of the example:

// HTML Form
<form method="post" action="process.php">
    <input type="text" name="username" />
    <input type="password" name="password" />
    <input type="submit" value="Submit" />
</form>

// process.php
<?php
echo "Username: " . $_POST['username'];
echo "Password: " . $_POST['password'];
?>

Here, $_POST['username'] retrieves the value of the username field, and $_POST['password'] retrieves the password entered by the user.

Important Notes:

• $_POST is suitable for submitting larger amounts of data and sensitive information.
• Data submitted via POST is not limited in size (unlike GET).

3. $_REQUEST - Get Data from GET, POST, and COOKIE

The $_REQUEST superglobal is a combination of $_GET, $_POST, and $_COOKIE. It contains data from all three sources. However, it is considered less secure than $_GET and $_POST since it may include unwanted data from cookies or GET variables. $_REQUEST is useful when you want to access both GET and POST data in one place.

Now, let us understand with the help of the example:

// URL: index.php?name=John
// and form with POST method: <input type="text" name="email" />

<?php
echo "Name: " . $_REQUEST['name']; // Retrieves from URL (GET)
echo "Email: " . $_REQUEST['email']; // Retrieves from Form (POST)
?>

Important Notes:

• It is advisable to use $_GET, $_POST, or $_COOKIE directly for better control and security over the data.

4. $_SERVER - Server and Execution Environment Information

The $_SERVER superglobal contains information about the server environment, request headers, and other system information. It provides details like the server name, request method, script name, and more. It is useful for accessing server information like HTTP headers, IP addresses, and other environment variables.

Now, let us understand with the help of the example:

<?php
   echo "Server Name: " . $_SERVER['SERVER_NAME'];  // Output: localhost
   echo "Request Method: " . $_SERVER['REQUEST_METHOD'];  // Output: GET

?>

Important Notes:

• $_SERVER also provides valuable information like $_SERVER['HTTP_USER_AGENT'], which contains details about the browser making the request.

5. $_FILES - File Uploads

The $_FILES superglobal is used to collect file upload data. It stores information about files uploaded via the HTML form using the enctype="multipart/form-data" attribute. It is used when a user uploads a file via a form, PHP stores metadata such as file name, type, size, and temporary location.

Now, let us understand with the help of the example:

// HTML Form
<form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="fileToUpload" />
    <input type="submit" value="Upload File" />
</form>

// upload.php
<?php
if (isset($_FILES['fileToUpload'])) {
    $file_name = $_FILES['fileToUpload']['name'];
    $file_tmp = $_FILES['fileToUpload']['tmp_name'];
    echo "File Name: " . $file_name;
    move_uploaded_file($file_tmp, "uploads/" . $file_name);
}
?>

Important Notes:

• $_FILES provides information like $_FILES['fileToUpload']['error'] for error handling during file upload.
• You should always validate and sanitize uploaded files to prevent security risks.

6. $_ENV - Environment Variables

The $_ENV superglobal contains environment variables that are available in your server's environment. These can include variables like the system path, PHP configuration settings, or other server-related settings. It is used to access server-specific settings or to manage configuration settings in different environments (e.g., development, production).

Now, let us understand with the help of the example:

<?php
   echo "PHP Version: " . $_ENV['PHP_VERSION'];  // Output: 7.4.3

?>

Important Notes:

• $_ENV is often used in conjunction with environment configuration files like .env files in modern PHP applications.

7. $_COOKIE - Handle Cookies

The $_COOKIE superglobal allows you to retrieve data stored in cookies. Cookies are small files stored on the user's device, and they can be used to persist data across different sessions. It is used when you want to store user preferences or login states between page reloads.

Now, let us understand with the help of the example:

<?php
setcookie("user", "gfg", time() + 3600, "/");

if (isset($_COOKIE['user'])) {
    echo "User: " . $_COOKIE['user'];  
}
?>
?>

Important Notes:

• Cookies are sent with HTTP requests and can persist between sessions until they expire.

8. $_SESSION - Session Variables

The $_SESSION superglobal is used to store session variables, which persist across multiple pages for the duration of the user's session. Session variables are typically used for user authentication and storing data across page visits. It is used for managing user login states, preferences, or temporary data that should persist across multiple page requests.

Now, let us understand with the help of the example:

<?php
session_start();
$_SESSION['username'] = "gfg";
echo $_SESSION['username'];  

?>

Important Notes:

• $_SESSION data is stored on the server and can be used to manage user sessions in a secure manner.
• Always start a session with session_start() before using $_SESSION.

Conclusion

PHP superglobals provide a convenient way to access global data without the need for explicitly passing variables between different parts of your script. By understanding and properly using these superglobals ($_GET, $_POST, $_REQUEST, $_SERVER, $_FILES, $_ENV, $_COOKIE, $_SESSION), developers can efficiently handle data from forms, server environments, user sessions, and more.

It’s important to be cautious when handling data from superglobals, especially with $_GET and $_POST, as they may contain sensitive user input. Always validate and sanitize user inputs to ensure security in your application.