How to Set Session Variable in PHP: Simple Guide

To set a session variable in PHP, first start the session using session_start(). Then assign a value to a session variable using the $_SESSION superglobal array, like $_SESSION['key'] = 'value';.

Syntax

To set a session variable in PHP, you must first start the session with session_start(). Then you can assign values to the $_SESSION array using a key and value.

• session_start(); - Initializes the session or resumes the current one.
• $_SESSION['key'] = 'value'; - Sets a session variable with the name 'key' and assigns it the value 'value'.

php

<?php
session_start();
$_SESSION['username'] = 'Alice';
?>

Example

This example shows how to start a session, set a session variable, and then display it on the page.

php

<?php
session_start();
$_SESSION['favorite_color'] = 'blue';
echo 'Your favorite color is ' . $_SESSION['favorite_color'] . '.';
?>

Output

Your favorite color is blue.

Common Pitfalls

Common mistakes when setting session variables include:

• Not calling session_start() before accessing $_SESSION.
• Trying to set session variables after outputting HTML, which causes headers to be sent and session start to fail.
• Forgetting that session variables persist across pages until the session ends or variables are unset.

php

<?php
// Wrong way: session_start() missing
// $_SESSION['user'] = 'Bob'; // This will cause an error or not work properly

// Right way:
session_start();
$_SESSION['user'] = 'Bob';
?>

Quick Reference

Step	Description	Code Example
1	Start or resume session	session_start();
2	Set session variable	$_SESSION['key'] = 'value';
3	Access session variable	echo $_SESSION['key'];
4	Unset session variable	unset($_SESSION['key']);
5	Destroy session	session_destroy();

Key Takeaways

Always call session_start() before setting or accessing session variables.

Use the $_SESSION superglobal array to set session variables with key-value pairs.

Session variables persist across pages until unset or session is destroyed.

Avoid outputting HTML before session_start() to prevent errors.

Use unset() or session_destroy() to remove session data when needed.