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A session is a term referring to
a user's time browsing a website.

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It's meant to represent the time between
a user's first page view on a particular

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site until the time when that
user is finished at that site.

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It's impossible to know for
sure when a user is done with a site.

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Instead, the session is
terminated in one of two ways.

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Either the user closes the browser, or
the session times out when a request

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has not been made within
a certain amount of time.

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By default, a PHP session is set
to timeout after 1440 seconds,

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which is 24 minutes.

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PHP offers us the ability to set
variables that are available for

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the duration of a user's session.

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These are called session variables.

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Let's go back into workspaces and set some
session variables based on user input.

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Open play.php.

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To access sessions,
we first need to start the session.

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We use session_start.

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This should be called before anything
is output to the browser, so

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it's usually best to place this
call at the top of the file.

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Next, we check if a word
has been posted if

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(isset($_POST['word'])).

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If so we can add a session variable,
$_SESSION['word'].

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We can use the page variable to define
which word this is, either by adding it to

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the variable name itself, +$page, or
by making the session variable an array.

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Since we post to the page number
after the word, we should use page-1.

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Then as always, filter user input.

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INPUT_POST.

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'Word'.

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FILTER_SANITIZE_STRING.

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To make sure our session is working,
let's var_dump the session variable.

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Now, let's try out our
game in the browser again.

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After we enter the word and push Submit,

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we can see that our session
variable word is an array.

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The key of one equals our first word.

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Let's go back to workspaces and use these
variables in the story before we continue.

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We can remove our var_dump and
open story.php.

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At the top we have five word variables.

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Let's set these variables
to the session variable.

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We start by adding a session_start
to the top of the file.

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We also want to escape our user data so
we use the function htmlspecialchars,

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_SESSION['word][1].

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Let's finish running through our game now.

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Great, we keep track of each
word the user enters and

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then use those words to write our story.

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There's one last thing
that we should look at.

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That is, removing session variables.

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If the user chooses Play Again, we should
clear the current session variables.

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Let's go back to play.php If they come

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to this page without a p parameter,
we should clear the session variable.

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We can clear individual session variables
just like we would any other variable,

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either setting them to an empty variable.

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Or calling the unset
function on that variable.

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To unset all session variables at once,
we should instead,

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use the function session_destroy.

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Now, let's go back to the browser.

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If we navigate to the welcome page.

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And then go back to the story,
the session variables are still set.

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If we choose Play Again and
then go back to our story,

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the errosr show us that the session
variables are no longer available.

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This also shows us some more logic we
should add, making sure that the required

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session variables are set before
attempting to write the story.