What Is PHP Session

A session is a way to store information (in variables) to be used across multiple pages. Unlike a cookie, the information is not stored on the users' computer. Session variables hold information about one single user and are available to all pages in one application.

Starting a PHP Session:

A session is started with the session_start() function. This function must be the very first thing in your document, before any HTML tags.

<?php
// Start the session
session_start();
?>
<!DOCTYPE html>
<html>
<body>
...

Storing Session Data:

Session variables are set with the PHP global variable: $_SESSION.

<?php
// Start the session
session_start();

// Set session variables
$_SESSION["favcolor"] = "green";
$_SESSION["favanimal"] = "cat";
echo "Session variables are set.";
?>

Accessing Session Data:

To access session variables, you just need to refer to the $_SESSION variable.

<?php
// Start the session
session_start();

// Echo session variables that were set on previous page
echo "Favorite color is " . $_SESSION["favcolor"] . ".<br>";
echo "Favorite animal is " . $_SESSION["favanimal"] . ".";
?>

Destroying a PHP Session:

To remove all global session variables and destroy the session, use session_unset() and session_destroy().

<?php
// Start the session
session_start();

// Remove all session variables
session_unset();

// Destroy the session
session_destroy(); 
?>

In this case, session_unset() removes all session variables and session_destroy() destroys the session. After this code is executed, the session will no longer exist, and any further attempts to access session variables will fail until a new session is started.

Note:

Session data is not meant to be permanent storage. The server may delete the session data if it needs to reclaim disk space or if the session has been idle for too long. Always have a backup method to access the data in case the session data is deleted.

PHP session variables example:

Example demonstrating the use of session variables to store and retrieve data across multiple requests.

// File: start_session.php
session_start();

// Set session variables
$_SESSION['username'] = 'john_doe';
$_SESSION['user_id'] = 123;

// Access session variables
echo "Welcome, " . $_SESSION['username'];

// File: another_page.php
session_start();

// Access session variables across pages
echo "User ID: " . $_SESSION['user_id'];

session_start() function in PHP:
- Use session_start() at the beginning of each script to start or resume a session.
```
// File: index.php
session_start();

// Perform operations with session variables
```

Manage sessions in PHP:

Use $_SESSION superglobal to manage and store session variables.

session_start();

// Set session variable
$_SESSION['language'] = 'English';

// Access session variable
echo "Current language: " . $_SESSION['language'];

PHP session timeout configuration:

Configure session timeout using session.gc_maxlifetime in php.ini or using ini_set().

// File: start_session.php
ini_set('session.gc_maxlifetime', 3600); // 1 hour
session_start();

// Perform operations with session variables

session_destroy() in PHP:
- Use session_destroy() to end the current session and clear session data.
```
// File: logout.php
session_start();
session_destroy();
```

PHP session handling for login/logout:

Implement session handling for user login and logout.

// File: login.php
session_start();

// Authenticate user
if ($authenticated) {
    $_SESSION['user_id'] = $user_id;
    $_SESSION['username'] = $username;
}

// File: logout.php
session_start();
session_destroy();

Cookies vs sessions in PHP:

Compare cookies and sessions for data persistence and security considerations.

// Using cookies
setcookie('username', 'john_doe', time() + 3600, '/');

// Accessing cookie value
echo "Welcome, " . $_COOKIE['username'];

// Using sessions
session_start();
$_SESSION['username'] = 'john_doe';

// Accessing session value
echo "Welcome, " . $_SESSION['username'];