# Basic usage ## Installation To install Composer, you just need to download the `composer.phar` executable. $ curl -sS https://getcomposer.org/installer | php For the details, see the [Introduction](00-intro.md) chapter. To check if Composer is working, just run the PHAR through `php`: $ php composer.phar This should give you a list of available commands. > **Note:** You can also perform the checks only without downloading Composer > by using the `--check` option. For more information, just use `--help`. > > $ curl -sS https://getcomposer.org/installer | php -- --help ## `composer.json`: Project Setup To start using Composer in your project, all you need is a `composer.json` file. This file describes the dependencies of your project and may contain other metadata as well. The [JSON format](http://json.org/) is quite easy to write. It allows you to define nested structures. ### The `require` Key The first (and often only) thing you specify in `composer.json` is the `require` key. You're simply telling Composer which packages your project depends on. { "require": { "monolog/monolog": "1.0.*" } } As you can see, `require` takes an object that maps **package names** (e.g. `monolog/monolog`) to **package versions** (e.g. `1.0.*`). ### Package Names The package name consists of a vendor name and the project's name. Often these will be identical - the vendor name just exists to prevent naming clashes. It allows two different people to create a library named `json`, which would then just be named `igorw/json` and `seldaek/json`. Here we are requiring `monolog/monolog`, so the vendor name is the same as the project's name. For projects with a unique name this is recommended. It also allows adding more related projects under the same namespace later on. If you are maintaining a library, this would make it really easy to split it up into smaller decoupled parts. ### Package Versions We are requiring version `1.0.*` of monolog. This means any version in the `1.0` development branch. It would match `1.0.0`, `1.0.2` or `1.0.20`. Version constraints can be specified in a few different ways. * **Exact version:** You can specify the exact version of a package, for example `1.0.2`. * **Range:** By using comparison operators you can specify ranges of valid versions. Valid operators are `>`, `>=`, `<`, `<=`, `!=`. An example range would be `>=1.0`. You can define multiple ranges, separated by a comma: `>=1.0,<2.0`. * **Wildcard:** You can specify a pattern with a `*` wildcard. `1.0.*` is the equivalent of `>=1.0,<1.1`. * **Next Significant Release (Tilde Operator):** The `~` operator is best explained by example: `~1.2` is equivalent to `>=1.2,<2.0`, while `~1.2.3` is equivalent to `>=1.2.3,<1.3`. As you can see it is mostly useful for projects respecting [semantic versioning](http://semver.org/). A common usage would be to mark the minimum minor version you depend on, like `~1.2` (which allows anything up to, but not including, 2.0). Since in theory there should be no backwards compatibility breaks until 2.0, that works well. Another way of looking at it is that using `~` specifies a minimum version, but allows the last digit specified to go up. By default only stable releases are taken into consideration. If you would like to also get RC, beta, alpha or dev versions of your dependencies you can do so using [stability flags](04-schema.md#package-links). To change that for all packages instead of doing per dependency you can also use the [minimum-stability](04-schema.md#minimum-stability) setting. ## Installing Dependencies To fetch the defined dependencies into your local project, just run the `install` command of `composer.phar`. $ php composer.phar install This will find the latest version of `monolog/monolog` that matches the supplied version constraint and download it into the `vendor` directory. It's a convention to put third party code into a directory named `vendor`. In case of monolog it will put it into `vendor/monolog/monolog`. > **Tip:** If you are using git for your project, you probably want to add > `vendor` into your `.gitignore`. You really don't want to add all of that > code to your repository. Another thing that the `install` command does is it adds a `composer.lock` file into your project root. ## `composer.lock` - The Lock File After installing the dependencies, Composer writes the list of the exact versions it installed into a `composer.lock` file. This locks the project to those specific versions. **Commit your application's `composer.lock` (along with `composer.json`) into version control.** This is important because the `install` command checks if a lock file is present, and if it is, it downloads the versions specified there (regardless of what `composer.json` says). This means that anyone who sets up the project will download the exact same version of the dependencies. Your CI server, production machines, other developers in your team, everything and everyone runs on the same dependencies, which mitigates the potential for bugs affecting only some parts of the deployments. Even if you develop alone, in six months when reinstalling the project you can feel confident the dependencies installed are still working even if your dependencies released many new versions since then. If no `composer.lock` file exists, Composer will read the dependencies and versions from `composer.json` and create the lock file. This means that if any of the dependencies get a new version, you won't get the updates automatically. To update to the new version, use `update` command. This will fetch the latest matching versions (according to your `composer.json` file) and also update the lock file with the new version. $ php composer.phar update If you only want to install or update one dependency, you can whitelist them: $ php composer.phar update monolog/monolog [...] > **Note:** For libraries it is not necessarily recommended to commit the lock file, > see also: [Libraries - Lock file](02-libraries.md#lock-file). ## Packagist [Packagist](https://packagist.org/) is the main Composer repository. A Composer repository is basically a package source: a place where you can get packages from. Packagist aims to be the central repository that everybody uses. This means that you can automatically `require` any package that is available there. If you go to the [packagist website](https://packagist.org/) (packagist.org), you can browse and search for packages. Any open source project using Composer should publish their packages on packagist. A library doesn't need to be on packagist to be used by Composer, but it makes life quite a bit simpler. ## Autoloading For libraries that specify autoload information, Composer generates a `vendor/autoload.php` file. You can simply include this file and you will get autoloading for free. require 'vendor/autoload.php'; This makes it really easy to use third party code. For example: If your project depends on monolog, you can just start using classes from it, and they will be autoloaded. $log = new Monolog\Logger('name'); $log->pushHandler(new Monolog\Handler\StreamHandler('app.log', Monolog\Logger::WARNING)); $log->addWarning('Foo'); You can even add your own code to the autoloader by adding an `autoload` field to `composer.json`. { "autoload": { "psr-0": {"Acme\\": "src/"} } } Composer will register a [PSR-0](https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md) autoloader for the `Acme` namespace. You define a mapping from namespaces to directories. The `src` directory would be in your project root, on the same level as `vendor` directory is. An example filename would be `src/Acme/Foo.php` containing an `Acme\Foo` class. After adding the `autoload` field, you have to re-run `install` to re-generate the `vendor/autoload.php` file. Including that file will also return the autoloader instance, so you can store the return value of the include call in a variable and add more namespaces. This can be useful for autoloading classes in a test suite, for example. $loader = require 'vendor/autoload.php'; $loader->add('Acme\\Test\\', __DIR__); In addition to PSR-0 autoloading, classmap is also supported. This allows classes to be autoloaded even if they do not conform to PSR-0. See the [autoload reference](04-schema.md#autoload) for more details. > **Note:** Composer provides its own autoloader. If you don't want to use that one, you can just include `vendor/composer/autoload_namespaces.php`, which returns an associative array mapping namespaces to directories. ← [Intro](00-intro.md) | [Libraries](02-libraries.md) →