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6.8 PHP Sessions

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.

What is a PHP Session?

When you work with an application, you open it, do some changes, and then you close it. This is much like a Session. The computer knows who you are. It knows when you start the application and when you end. But on the internet there is one problem: the web server does not know who you are or what you do, because the HTTP address doesn't maintain state.
Session variables solve this problem by storing user information to be used across multiple pages (e.g. username, favorite color, etc). By default, session variables last until the user closes the browser.
So; Session variables hold information about one single user, and are available to all pages in one application.

Start a PHP Session

A session is started with the session_start() function.
Session variables are set with the PHP global variable: $_SESSION.
Now, let's create a new page called "demo_session1.php". In this page, we start a new PHP session and set some session variables:

Example 1: PHP Sessions - Start a PHP Session

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

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

</body>
</html>

Note: The session_start() function must be the very first thing in your document. Before any HTML tags.

Get PHP Session Variable Values

Next, we create another page called "demo_session2.php". From this page, we will access the session information we set on the first page ("demo_session1.php").
Notice that session variables are not passed individually to each new page, instead they are retrieved from the session we open at the beginning of each page (session_start()).
Also notice that all session variable values are stored in the global $_SESSION variable:

Example 2: PHP Sessions - Get PHP Session Variable Values

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

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

</body>
</html>

Another way to show all the session variable values for a user session is to run the following code:

Example 3: PHP Sessions - Get PHP Session Variable Values part 2

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
print_r($_SESSION);
?>

</body>
</html>

How does it work? How does it know it's me?
Most sessions set a user-key on the user's computer that looks something like this: 765487cf34ert8dede5a562e4f3a7e12. Then, when a session is opened on another page, it scans the computer for a user-key. If there is a match, it accesses that session, if not, it starts a new session.

Modify a PHP Session Variable

To change a session variable, just overwrite it:

Example 4: PHP Sessions - Modify a PHP Session Variable

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// to change a session variable, just overwrite it
$_SESSION["favcolor"] = "yellow";
print_r($_SESSION);
?>

</body>
</html>

Destroy a PHP Session

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

Example 5: PHP Sessions - Destroy a PHP Session

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// remove all session variables
session_unset();

// destroy the session
session_destroy();
?>

</body>
</html>

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Module 6. PHP Advanced

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Example files created in this module:
The PHP Date() Function - Get a Date The PHP Date() Function - Automatic Copyright Year The PHP Date() Function - Get a Time The PHP Date() Function - Get Your Time Zone The PHP Date() Function - Create a Date With mktime() The PHP Date() Function - Create a Date From a String With strtotime() part 1 The PHP Date() Function - Create a Date From a String With strtotime()part 2 The PHP Date() Function - Create Dates From Strings With strtotime() The PHP Date() Function - Count The Number of Days To July 4 With strtotime() PHP Include Files - PHP include Example part 1 PHP Include Files - PHP include Example part 2 PHP Include Files - PHP include Example part 3 PHP Include Files - PHP include Example part 4 PHP Include Files - PHP require Example readfile() fopen() fgets() feof() fgetc() PHP File Handling - PHP readfile() Function PHP File Open/Read - PHP Open File - fopen() PHP File Open/Read - fgets() Read Single Line PHP File Open/Read - feof() Check End-Of-File PHP File Open/Read - fgetc() Read Single Character PHP File Upload PHP Cookies - Create/Retrieve a Cookie PHP Cookies - Modify a Cookie Value PHP Cookies - Delete a Cookie PHP Cookies - Check if Cookies are Enabled PHP Sessions - Start a PHP Session PHP Sessions - Get PHP Session Variable Values part 1 PHP Sessions - Get PHP Session Variable Values part 2 PHP Sessions - Modify a PHP Session Variable PHP Sessions - Destroy a PHP Session PHP Filters - The PHP Filter Extension PHP Filters - Sanitize a String PHP Filters - Validate an Integer PHP Filters - filter_var() and Problem With 0 PHP Filters - Validate an IP Address PHP Filters - Sanitize and Validate an Email Address PHP Filters - Sanitize and Validate a URL PHP Filters Advanced - Validate an Integer Within a Range PHP Filters Advanced - Validate IPv6 Address PHP Filters Advanced - Validate URL That Must Contain QueryString PHP Filters Advanced - Remove Characters With ASCII Value > 127 PHP Callback Functions PHP Callback Functions - Anonymous Function PHP Callback Functions - Callbacks in User Defined Functions PHP and JSON - json_encode() part 1 PHP and JSON - json_encode() part 2 PHP and JSON - json_decode() part 1 PHP and JSON - json_decode() part 2 PHP and JSON - Accessing the Decoded Values part 1 PHP and JSON - Accessing the Decoded Values part 2 PHP and JSON - Looping Through the Values part 1 PHP and JSON - Looping Through the Values part 2 PHP Exceptions - Throwing an Exception PHP Exceptions - The try...catch Statement PHP Exceptions - The try...catch...finally Statement part 1 PHP Exceptions - The try...catch...finally Statement part 2 PHP Exceptions - The Exception Object