Composer Basics

Install Composer

Follow getcomposer.org for your OS, then verify the CLI.

composer --version

Create a project manifest

In an empty folder, initialize composer.json.

composer init
# or quickly:
composer require monolog/monolog

Use the autoloader

Require Composer's autoload file once, then use classes from packages.

<?php
require __DIR__ . "/vendor/autoload.php";

use Monolog\Logger;
use Monolog\Handler\StreamHandler;

$log = new Logger("app");
$log->pushHandler(new StreamHandler("app.log", Logger::INFO));
$log->info("Composer works");

Composer habits

• Commit composer.json and composer.lock
• Do not commit vendor/ in many workflows—run composer install
• PSR-4 autoloading maps namespaces to folders
• Prefer Packagist packages with clear maintenance signals