composer/doc/01-basic-usage.md

Basic usage

Installation

To install composer, simply run this command on the command line:

$ curl -s http://getcomposer.org/installer | php

This will perform some checks on your environment to make sure you can actually run it.

Then it will download composer.phar and place it in your working directory. composer.phar is the composer binary. It is a PHAR (PHP archive), which is an archive format for PHP which can be run on the command line, amongst other things.

You can place this file anywhere you wish. If you put it in your PATH, you can access it globally. On unixy systems you can even make it executable and invoke it without php.

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 -s http://getcomposer.org/installer | php -- --help

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 is quite easy to write. It allows you to define nested structures.

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 to versions.

Package names

The package name consists of a vendor name and the project's name. Often these will be identical. The vendor name 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 also requiring the version 1.0.* of monolog. This means any version in the 1.0 development branch. It would match 1.0.0, 1.0.2 and 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. This is not used very often, but can be useful.

• 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 of these, separated by comma: >=1.0,<2.0.

• Wildcard: You can specify a pattern with a * wildcard. 1.0.* is the equivalent of >=1.0,<1.1-dev.

Installing dependencies

To fetch the defined dependencies into the local project, you simply 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 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.

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 project's composer.lock into version control.

The reason is that anyone who sets up the project should get the same version. The install command will check if a lock file is present. If it is, it will use the versions specified there. If not, it will resolve the dependencies and create a lock file.

If any of the dependencies gets a new version, you can update to that version by using the update command. This will fetch the latest matching versions and also update the lock file.

$ php composer.phar update

Packagist

Packagist 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 (packagist.org), you can browse and search for packages.

Any open source project using composer should publish their packages on packagist.

Autoloading

For libraries that follow the PSR-0 naming standard, composer generates a vendor/.composer/autoload.php file for autoloading. You can simply include this file and you will get autoloading for free.

require 'vendor/.composer/autoload.php';

This makes it really easy to use third party code, because you only have to add one line to composer.json and run install. For monolog, it means that we 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', 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/"}
    }
}

This is a mapping from namespaces to directories. The src directory would be in your project root. 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/.composer/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/.composer/autoload.php';
$loader->add('Acme\Test', __DIR__);

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.

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