148 lines
3.2 KiB
Markdown
148 lines
3.2 KiB
Markdown
|
---
|
||
|
|
title: PHP Sessions
|
||
|
|
---
|
||
|
|
|
||
|
|
# 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 user's 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.
|
||
|
|
|
||
|
|
**Session variables hold information about one single user, and are available to all pages in one application.**
|
||
|
|
|
||
|
|
**Note:** If you need a permanent storage, you may want to store the data in a database.
|
||
|
|
|
||
|
|
|
||
|
|
## Start a PHP Session
|
||
|
|
|
||
|
|
A session is started with the _session_start()_ function.
|
||
|
|
Session variables are set with the PHP global variable: $_SESSION.
|
||
|
|
|
||
|
|
**Example:**
|
||
|
|
```
|
||
|
|
<?php
|
||
|
|
// Start the session
|
||
|
|
session_start();
|
||
|
|
?>
|
||
|
|
<!DOCTYPE html>
|
||
|
|
<html>
|
||
|
|
<body>
|
||
|
|
|
||
|
|
<?php
|
||
|
|
// Set session variables
|
||
|
|
$_SESSION["favcolor"] = "blue";
|
||
|
|
$_SESSION["favanimal"] = "dog";
|
||
|
|
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.
|
||
|
|
|
||
|
|
Output:
|
||
|
|
Session variables are set.
|
||
|
|
|
||
|
|
|
||
|
|
## Get PHP Session Variable Values
|
||
|
|
|
||
|
|
Note 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 note that all session variable values are stored in the global $_SESSION variable:
|
||
|
|
|
||
|
|
**Example:**
|
||
|
|
```
|
||
|
|
<?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 " . $_SESSION["favanimal"] . ".";
|
||
|
|
?>
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
```
|
||
|
|
|
||
|
|
Output:
|
||
|
|
Favorite color is blue.
|
||
|
|
Favorite animal is dog.
|
||
|
|
|
||
|
|
Another way to show all the session variable values for a user session is to run the following code:
|
||
|
|
|
||
|
|
```
|
||
|
|
<?php
|
||
|
|
print_r($_SESSION);
|
||
|
|
?>
|
||
|
|
```
|
||
|
|
|
||
|
|
### How does it work?
|
||
|
|
|
||
|
|
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 Session Variable
|
||
|
|
|
||
|
|
To change a session variable, just overwrite it:
|
||
|
|
|
||
|
|
**Example:**
|
||
|
|
```
|
||
|
|
<?php
|
||
|
|
session_start();
|
||
|
|
?>
|
||
|
|
<!DOCTYPE html>
|
||
|
|
<html>
|
||
|
|
<body>
|
||
|
|
|
||
|
|
<?php
|
||
|
|
// to change a session variable, just overwrite it
|
||
|
|
$_SESSION["favcolor"] = "pink";
|
||
|
|
print_r($_SESSION);
|
||
|
|
?>
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
```
|
||
|
|
|
||
|
|
|
||
|
|
## Destroy a PHP Session
|
||
|
|
|
||
|
|
To remove all global session variables and destroy the session, use _session_unset()_ and _session_destroy()_:
|
||
|
|
|
||
|
|
**Example:**
|
||
|
|
```
|
||
|
|
<?php
|
||
|
|
session_start();
|
||
|
|
?>
|
||
|
|
<!DOCTYPE html>
|
||
|
|
<html>
|
||
|
|
<body>
|
||
|
|
|
||
|
|
<?php
|
||
|
|
// remove all session variables
|
||
|
|
session_unset();
|
||
|
|
|
||
|
|
// destroy the session
|
||
|
|
session_destroy();
|
||
|
|
?>
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|
||
|
|
```
|