PHP
5 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.
Tip: 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.
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
<?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
<?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 " . $_SESSION["favanimal"] .
".";
?>
</body>
</html>
Another way
to show all the session variable values for a user session is to run the
following code:
Example
<?php
session_start();
?>
<!DOCTYPE
html>
<html>
<body>
<?php
print_r($_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
<?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
<?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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