Menyertakan dan Memerlukan Fail

<?php
// Fatal error if missing — use for critical files
require 'config.php';
require 'database.php';

// Warning if missing, but execution continues
include 'optional_plugin.php';

// Use __DIR__ for reliable relative paths:
require __DIR__ . '/helpers/utils.php';

<?php
// Without _once: including twice redefines functions
include 'functions.php';
include 'functions.php';  // Fatal: function redefined!

// With _once: second include is a no-op
require_once 'functions.php';
require_once 'functions.php';  // safe — skipped

// Rule: use require_once for class and function definition files

<?php
// main.php
$title = 'My Site';
require 'header.php';  // header.php can use $title

// But in a function:
function loadTemplate(): void {
    require 'header.php';  // $title is NOT accessible here!
    // Must pass data explicitly
}

<?php
// config.php content:
// return ['debug' => true, 'db_host' => 'localhost'];

// main.php:
$config = require 'config.php';
echo $config['db_host'];  // localhost

// Common pattern for configuration files that return arrays

<?php
// index.php
$pageTitle = 'Home Page';
$bodyClass = 'home';

require_once 'partials/header.php';
?>

<main class="container">
    <h1>Welcome!</h1>
    <p>Main content goes here.</p>
</main>

<?php require_once 'partials/footer.php'; ?>

<?php
// partials/card.php
// Expects: $card['title'], $card['body'], $card['url']
?>

<div class="card">
    <h3><a href="<?= htmlspecialchars($card['url']) ?>">
        <?= htmlspecialchars($card['title']) ?>
    </a></h3>
    <p><?= htmlspecialchars($card['body']) ?></p>
</div>

<?php
$articles = getArticles();

foreach ($articles as $article) {
    $card = [
        'title' => $article['title'],
        'body'  => substr($article['body'], 0, 100) . '...',
        'url'   => '/articles/' . $article['slug'],
    ];
    require 'partials/card.php';
}

<?php
// Old way (manual includes):
require 'classes/User.php';
require 'classes/Post.php';

// Modern way (Composer autoloading):
require __DIR__ . '/vendor/autoload.php';

// Classes are loaded automatically when first used
$user = new User();  // User.php loaded by autoloader
$post = new Post();  // Post.php loaded by autoloader

<?php
// DANGEROUS:
$page = $_GET['page'];
include $page . '.php';  // allows ../../etc/passwd

// SAFE: whitelist allowed pages
$allowed = ['home', 'about', 'contact'];
$page = $_GET['page'] ?? 'home';

if (!in_array($page, $allowed)) {
    $page = 'home';
}

include __DIR__ . '/pages/' . $page . '.php';

<?php
// Current include_path:
echo get_include_path();

// Add your library directory:
set_include_path(
    get_include_path() . PATH_SEPARATOR . '/var/www/lib'
);

// Now you can include without full path:
include 'helpers.php';  // found in /var/www/lib/helpers.php