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PHP — session_id() Function

Sessions or session handling is a way to make the data available across various pages of a web application. The session_id() function is used to set or retrieve a custom id to the current.

Syntax

Parameters

This is a string value representing the id of the session, if you want to set id of the session using this method.

Return Values

This returns a String representing the id of the current session (if it has any) or, an empty string if current session doesn’t have any id.

PHP Version

This function was first introduced in PHP Version 4 and works in all the later versions.

Example 1

Following example demonstrates the usage of the session_id() function.

One executing the above html file it will display the following message −

Session Id: b9t3gprjtl35ms4sm937hj7s30

Example 2

Following is another example of this function, in here we have two pages from the same application in the same session.

 ?>   
Enter the values click Submit and click on Next 

Name: 
 
Age: 
 
 
Next'; ?>
   

This will produce the following output −

Once you press submit the page will be like −

On clicking on Next the following file is executed.

    "; print($_SESSION['name']); echo "
"; print($_SESSION['age']); ?>  

This will produce the following output −

Values from the session with id: brb9t3gprjtl35ms4sm937hj7s30 Krishna 30

Example 3

You can create a custom session id by using this function as shown below −

One executing the above html file it will display the following message −

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Функции для работы с сессиями

Be aware of the fact that absolute URLs are NOT automatically rewritten to contain the SID.

Of course, it says so in the documentation (‘Passing the Session Id’) and of course it makes perfectly sense to have that restriction, but here’s what happened to me:
I have been using sessions for quite a while without problems. When I used a global configuration file to be included in all my scripts, it contained a line like this:

which was used to make sure that all automatically generated links had the right prefix (just like $cfg[‘PmaAbsoluteUri’] works in phpMyAdmin). After introducing that variable, no link would pass the SID anymore, causing every script to return to the login page. It took me hours (!!) to recognize that this wasn’t a bug in my code or some misconfiguration in php.ini and then still some more time to find out what it was. The above restriction had completely slipped from my mind (if it ever was there. )

Skipping the ‘http:’ did the job.

OK, it was my own mistake, of course, but it just shows you how easily one can sabotage his own work for hours. Just don’t do it 😉

Sessions and browser’s tabs

May you have noticed when you open your website in two or more tabs in Firefox, Opera, IE 7.0 or use ‘Control+N’ in IE 6.0 to open a new window, it is using the same cookie or is passing the same session id, so the another tab is just a copy of the previous tab. What you do in one will affect the another and vice-versa. Even if you open Firefox again, it will use the same cookie of the previous session. But that is not what you need mostly of time, specially when you want to copy information from one place to another in your web application. This occurs because the default session name is «PHPSESSID» and all tabs will use it. There is a workaround and it rely only on changing the session’s name.

Put these lines in the top of your main script (the script that call the subscripts) or on top of each script you have:

if( version_compare ( phpversion (), ‘4.3.0’ )>= 0 ) <
if(! ereg ( ‘^SESS7+$’ , $_REQUEST [ ‘SESSION_NAME’ ])) <
$_REQUEST [ ‘SESSION_NAME’ ]= ‘SESS’ . uniqid ( » );
>
output_add_rewrite_var ( ‘SESSION_NAME’ , $_REQUEST [ ‘SESSION_NAME’ ]);
session_name ( $_REQUEST [ ‘SESSION_NAME’ ]);
>
?>

How it works:

First we compare if the PHP version is at least 4.3.0 (the function output_add_rewrite_var() is not available before this release).

After we check if the SESSION_NAME element in $_REQUEST array is a valid string in the format «SESSIONxxxxx», where xxxxx is an unique id, generated by the script. If SESSION_NAME is not valid (ie. not set yet), we set a value to it.

uniqid(») will generate an unique id for a new session name. It don’t need to be too strong like uniqid(rand(),TRUE), because all security rely in the session id, not in the session name. We only need here a different id for each session we open. Even getmypid() is enough to be used for this, but I don’t know if this may post a treat to the web server. I don’t think so.

output_add_rewrite_var() will add automatically a pair of ‘SESSION_NAME=SESSxxxxx’ to each link and web form in your website. But to work properly, you will need to add it manually to any header(‘location’) and Javascript code you have, like this:

The last function, session_name() will define the name of the actual session that the script will use.

So, every link, form, header() and Javascript code will forward the SESSION_NAME value to the next script and it will know which is the session it must use. If none is given, it will generate a new one (and so, create a new session to a new tab).

May you are asking why not use a cookie to pass the SESSION_NAME along with the session id instead. Well, the problem with cookie is that all tabs will share the same cookie to do it, and the sessions will mix anyway. Cookies will work partially if you set them in different paths and each cookie will be available in their own directories. But this will not make sessions in each tab completly separated from each other. Passing the session name through URL via GET and POST is the best way, I think.

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How to Get Session ID in php with session_id()

To get the session ID in php, you can use the php session_id() function. session_id() returns the session ID if a session is active.

session_start(); $session_id = session_id();

If you want to start a session with your own session ID, then you can use session_id() before you start a session with your own ID.

session_id($your_id); session_start();

Session handling is a big concept in php that allows us to handle and store user information across an entire website or web application.

When working with sessions, the ability to get the session ID is very useful.

In php, we can get the ID of a session easily with the session_id() function.

If there is a session active, session_id() returns the ID of the session.

Below is an example showing how you can get the session ID in php.

session_start(); $session_id = session_id();

You can also pass your own session ID if you want to initialize a session with a specific ID. You can replace the system-generated system ID with your own ID.

session_id($your_id); session_start();

Passing the Session ID Between Pages in php

After a session has been started for a user, many times we want to be able to store information about this user and also make sure that we can access this information in any page that is necessary.

There are two methods to propagate a session id: cookies and a URL parameter.

The session module supports both methods of session id propagation.

Sometimes a user will have cookies turned off, and so if this is the case, then php will use a URL query string parameter to pass the session id across pages.

To be able to access a session in all pages of your website or web application, you need to add session_start() at the top of all your php pages that needs to access the global SESSION array.

Then you can access session variables in the following way:

session_start(); // create session variables $_SESSION['user_id'] = '10'; $_SESSION['user_name'] = 'TheProgrammingExpert'; // get session variables echo $_SESSION['user_id']; echo $_SESSION['user_name'];

Hopefully this article has been useful for you to learn how to get the session id in php.

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Session ID in PHP

1. Check Session ID With session_id() Function
2. Set and Get a User Session ID From $_session[] Variable in PHP
3. Get Session ID With var_dump() in PHP
4. Session ID and Uniqueness

One of the main use of a session id is the identification of users or events on a web application. This article will explain how you can work with PHP session id with the help of built-in PHP functions like session_start() and session_id() .

Check Session ID With session_id() Function

Before you can check for a session ID, you need to start a PHP session with session_start() . Afterward, you can call on the session_id() function. This function will return the current session id.

php  session_start();   echo session_id(); ?> 

3rd5hnbqgjhi3fq4b2edsajq81 

Set and Get a User Session ID From $_session[] Variable in PHP

PHP $_SESSION variable is an associative array that contains the current script’s PHP session variables. You can add a specific key-value pair to the array, delete it from the array, or empty the entire $_SESSION variable.

You can store the details of authenticated users in the $_SESSION variable. Before that, you need to start a PHP session. Once the session is active, you can register a session for an authenticated user. Afterward, you can use the session id to track the user across the system. When the user logs out, you can destroy the session.

In the next code block, you’ll find details on how to set and get a user session id.

php  // Start the session  session_start();   // get the session id  $session_id = session_id();   // The username of the user. On most occasions,  // you'll get this from a MySQL query  $username = "DelftStack";   // Register a session for the user  $_SESSION['username'] = $username;   // Display the session id and the registered  // register  echo "The session id is: " . $session_id;  echo " 
The session has been registered to: " . $username; ?> 

The session id is: d7ao75228pobka332fqeho10l3 The session has been registered to: DelftStack 

Remember, your session id will be different than the one shown above.

You can destroy the session with the following code:

php  if (isset($_SESSION['username']))    // Reset the session  unset($_SESSION);   // Destroy the session  session_destroy();   if (empty($_SESSION))   echo "Session destroyed. ";  >  > ?> 

Get Session ID With var_dump() in PHP

The var_dump() function will dump the details about a variable, including the $_SESSION[] variable. Start the session and store the session id in a variable to get started with this process. Once the session id is in a variable, you can dump it with var_dump .

The next code block shows how to get session id with var_dump() .

php  // Start the session  session_start();   // get the session id  $session_id = session_id();   // store the session id in the  // session variable  $_SESSION['id'] = $session_id;   // Dump the username  var_dump($_SESSION['id']); ?> 

string(26) "7qfm3qvjj1vku6h78p73qh9jmn" 

Session ID and Uniqueness

It’s recommended not to start a new session when you need a unique identifier for a user. That’s when a function like uniqid() comes into play. But, if you have an active session, you can use session_id() . Still, do not rely on it for uniqueness.

Here is why: A web browser with multiple tabs will use the same process. As a result, they will use the same session identifier. It means different user connections will have the same id.

Habdul Hazeez is a technical writer with amazing research skills. He can connect the dots, and make sense of data that are scattered across different media.

Related Article — PHP Session

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