What is SESSION in PHP ?

What is SESSION ?

• A session is a mechanism to persist information across the different web pages to identify users as they navigate a site or app
• A PHP session stores data on the server rather than user's computer. 
• In a session based environment, every user is identified through a unique number called session identifier or SID. 
• The session IDs are randomly generated by the PHP engine

Starting a PHP Session

To begin a new session, simply call the PHP session_start() function. It will create a new session and generate a unique session ID for the user.

<?php
// Starting session
session_start();
?> 

Firstly, session_start() function checks to see if a session already exists by presence of a session ID. If session id exists, then it sets up the session variables and if doesn't, it starts a new session by creating a new session ID.

You must call the session_start() function at the beginning of the page.

Storing and Accessing Session Data

You can store all your session data as key-value pairs in the $_SESSION[] superglobal array.  

<?php
// Starting session
session_start();
 
// Storing session data
$_SESSION["firstname"] = "Shobhit";
$_SESSION["lastname"] = "Garg";
?>

To access the session data

<?php
// Starting session
session_start();
 
// Accessing session data
echo 'Hi, ' . $_SESSION["firstname"] . ' ' . $_SESSION["lastname"];
?>

Destroying a session

If you want to remove certain session data:

<?php
// Starting session
session_start();
 
// Removing session data
if(isset($_SESSION["lastname"])){
    unset($_SESSION["lastname"]);
}
?>

To destroy session completely:

<?php
// Starting session
session_start();
 
// Destroying session
session_destroy();
?>