# PHP Dependency Management (Composer)

**Composer** is a tool for dependency management in PHP. It allows you to declare the libraries your project depends on and it will manage (install/update) them for you.

---

## 1. The `composer.json` File
This file describes the dependencies of your project and may contain other metadata as well.

```json
{
    "require": {
        "monolog/monolog": "2.0.*"
    }
}
```

## 2. Basic Commands
*   `composer init`: Interactively creates a `composer.json` file.
*   `composer require <package>`: Adds a library to `composer.json` and installs it.
*   `composer install`: Installs dependencies defined in `composer.lock`. This is typically run after cloning a project.
*   `composer update`: Updates dependencies to the latest versions allowed by `composer.json` and updates the `composer.lock` file.

## 3. The `vendor` Directory
Composer installs all dependencies into a directory named `vendor`. You should generally add this directory to your `.gitignore` file.

## 4. Autoloading
Composer generates a `vendor/autoload.php` file. You can simply include this file and start using the classes from those libraries without extra work.

```php
require __DIR__ . '/vendor/autoload.php';

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

// create a log channel
$log = new Logger('name');
$log->pushHandler(new StreamHandler('app.log', Logger::WARNING));

// add records to the log
$log->warning('Foo');
```

[[programming/php/php]] [[programming/php/php-namespaces]]