PHP Include and Require

How it works

require fails when its required file cannot be loaded, while include has a different warning/failure behaviour. The _once forms avoid executing the same resolved file repeatedly in one request. Use __DIR__ for a fixed relative dependency instead of depending on the current working directory. Larger projects normally use an autoloader for classes. Never turn a query parameter into a code path.

Run it locally

Run this complete source locally with PHP 8.2 or newer. Save it using the filename shown and run the command below. PHP is not currently available in Bhylu’s browser playground. Apache and MySQL are not needed for an ordinary CLI example.

php -l include-require.php
php include-require.php

Download this source as a local PHP lab file. Keep lab files separate from the Bhylu project and production data.

Example

<?php
declare(strict_types=1);

require_once __DIR__ . "/lending-policy.php";
require_once __DIR__ . "/lending-policy.php";
echo maximumLoanDays(), " days\n";

Expected result

21 days

The helper is a second complete source file shown with the lesson. Loading it twice through require_once does not redeclare its function. The call then uses the explicitly named policy. The review writes both lab files into its private source directory; it does not include files from an external server or a visitor-supplied path.

Supporting file: lending-policy.php

<?php
declare(strict_types=1);

function maximumLoanDays(): int { return 21; }