Question

I have the following code to include pages dynamically:

<div id="content">
    <div id="aside">
        ...
    </div>

    <div id="main">
        <?php
        $page = (isset($_GET['page'])) ? sanitize($_GET['page']) : 'home';
        if (!include 'pages/'.$page.'.php') require 'pages/404.php';
        ?>
    </div>
</div>

As you can see, the #aside has static content.
I want to include a specific content for the #aside depending on the page selected. For example, if the user goes to ‘Home’ and ‘About’, I want the ‘default’ aside. But if the user goes to ‘Documents’ I want a ‘Sections’ aside.
I know I can just include each aside from every page, but that’s not effective. I also don’t want the user to be hable to set the aside as the main content, so they have to be in different folders or something.
I’d like to know an effective and not so complicated way to do this.

Thanks for taking your time to read this.

Answer 1

Thank you all for your answers and collaboration. Although none of the answers did exactly what I was looking for, they showed me other ways to approach this issue and guided me to decide what method to use.
I came up with what I think is the simpliest way to do this:

1. I set my folder structure as: pages/aside and pages/main
2. I set up an array($asides) with the aside files as the keys and the main content files as the values.
3. Then I check if the requested file exists in the main folder.
4. If it doesn’t exist, I redirect the user to the 404 page. If it does exist, I loop through $asides to see which aside is asigned to that main content page.
5. If it doesn’t belong to any of the establisged asides, then I include the default aside.

$asides = array(
        'aside1' => array('page1', 'page2', 'page3', 'page4'),
        'aside2' => array('page5', 'page6')
    );

$page = (!empty($_GET['p'])) ? sanitize($_GET['p']) : 'page1';

if (file_exists("pages/main/{$page}.php")) {

    foreach ($asides as $key => $value) {
        if (in_array($page, $asides[$key])) {
            $aside = $key;
            break;
        }
    }
    if (!isset($aside)) $aside = 'default';

?>
    <div id="aside"><?php require "pages/aside/{$aside}.php"; ?></div>
    <div id="main"><?php require "pages/main/{$page}.php"; ?></div>
<?php

} else {
    header('Location: ?p=404');
}

The bounty goes to Madara Uchiha because in my opinion, his answer is simple an effective. Thanks again to all of you who helped me with this issue.