Includes and File Organization

Modern applications usually use Composer autoloading for classes, but require, require_once, and returning arrays from PHP files still appear in real PHP projects and legacy code.

Loading A Helper File

helpers.php:

<?php

declare(strict_types=1);

function formatProductLine(array $product): string
{
    return $product['name'] . ': ' . $product['price_cents'] . ' cents';
}

report.php:

<?php

declare(strict_types=1);

require __DIR__ . '/helpers.php';

$product = ['name' => 'Notebook', 'price_cents' => 1299];

echo formatProductLine($product) . "\n";

// Prints:
// Notebook: 1299 cents

require loads the helper file before the function is called. If the file cannot be loaded, PHP stops with an error. That is usually what you want for required application code.

Use __DIR__ For Paths

Relative paths can break when a script is run from a different working directory. __DIR__ gives the directory of the current file.

<?php

require __DIR__ . '/helpers.php';

This is more reliable than require 'helpers.php'; because it does not depend on where the command was run from.

require_once

Use require_once when loading the same file twice would cause problems, such as defining the same function twice.

<?php

require_once __DIR__ . '/helpers.php';
require_once __DIR__ . '/helpers.php';

echo "Loaded once\n";

// Prints:
// Loaded once

Do not use includes to hide a messy design. If every file loads many other files in a surprising order, the project becomes hard to reason about.

Config Files That Return Arrays

A PHP file can return a value. This is common for simple configuration.

config.php:

<?php

return [
    'currency' => 'GBP',
    'items_per_page' => 20,
];

report.php:

<?php

$config = require __DIR__ . '/config.php';

echo $config['currency'] . "\n";

// Prints:
// GBP

This keeps configuration data separate from the code that uses it.

File Organization Rules

Put reusable functions in helper files. Put data or settings in config files. Put output and script flow in the main script.

Avoid helper files that print output as soon as they are required. Loading a file should normally define functions, return data, or bootstrap the application deliberately.

Common Mistakes

Do not build include paths from user input. That can become a file inclusion vulnerability.

Do not rely on the current working directory for important includes. Use __DIR__.

Do not include a file that has hidden side effects unless that is the point of the file and the name makes it obvious.

What You Should Be Able To Do

After this lesson, you should be able to:

• use require to load a helper file;
• use __DIR__ to build stable paths;
• explain when require_once is useful;
• return an array from a config file;
• separate reusable helper code from script output.