composer/doc/00-intro.md

Introduction

Composer is a tool for dependency management in PHP. It allows you to declare the dependent libraries your project needs and it will install them in your project for you.

Dependency management

Composer is not a package manager. Yes, it deals with "packages" or libraries, but it manages them on a per-project basis, installing them in a directory (e.g. vendor) inside your project. By default it will never install anything globally. Thus, it is a dependency manager.

This idea is not new and Composer is strongly inspired by node's npm and ruby's bundler. But there has not been such a tool for PHP.

The problem that Composer solves is this:

a) You have a project that depends on a number of libraries.

b) Some of those libraries depend on other libraries.

c) You declare the things you depend on.

d) Composer finds out which versions of which packages need to be installed, and installs them (meaning it downloads them into your project).

Declaring dependencies

Let's say you are creating a project, and you need a library that does logging. You decide to use monolog. In order to add it to your project, all you need to do is create a composer.json file which describes the project's dependencies.

{
    "require": {
        "monolog/monolog": "1.2.*"
    }
}

We are simply stating that our project requires some monolog/monolog package, any version beginning with 1.2.

System Requirements

Composer requires PHP 5.3.2+ to run. A few sensitive php settings and compile flags are also required, but when using the installer you will be warned about any incompatibilities.

To install packages from sources instead of simple zip archives, you will need git, svn or hg depending on how the package is version-controlled.

Composer is multi-platform and we strive to make it run equally well on Windows, Linux and OSX.

Installation - Linux / Unix / OSX

Downloading the Composer Executable

There are in short, two ways to install Composer. Locally as part of your project, or globally as a system wide executable.

Locally

Installing Composer locally is a matter of just running the installer in your project directory:

curl -sS https://getcomposer.org/installer | php

Note: If the above fails for some reason, you can download the installer with php instead:

php -r "readfile('https://getcomposer.org/installer');" | php

The installer will just check a few PHP settings and then download composer.phar to your working directory. This file 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 install Composer to a specific directory by using the --install-dir option and providing a target directory (it can be an absolute or relative path):

curl -sS https://getcomposer.org/installer | php -- --install-dir=bin

Globally

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.

You can run these commands to easily access composer from anywhere on your system:

curl -sS https://getcomposer.org/installer | php
mv composer.phar /usr/local/bin/composer

Note: If the above fails due to permissions, run the mv line again with sudo.

Note: In OSX Yosemite the /usr directory does not exist by default. If you receive the error "/usr/local/bin/composer: No such file or directory" then you must create /usr/local/bin/ manually before proceeding.

Then, just run composer in order to run Composer instead of php composer.phar.

Installation - Windows

Using the Installer

This is the easiest way to get Composer set up on your machine.

Download and run Composer-Setup.exe, it will install the latest Composer version and set up your PATH so that you can just call composer from any directory in your command line.

Note: Close your current terminal. Test usage with a new terminal: That is important since the PATH only gets loaded when the terminal starts.

Manual Installation

Change to a directory on your PATH and run the install snippet to download composer.phar:

C:\Users\username>cd C:\bin
C:\bin>php -r "readfile('https://getcomposer.org/installer');" | php

Note: If the above fails due to readfile, enable php_openssl.dll in php.ini. You may use the http URL, however this will leave the request susceptible to a Man-In-The-Middle (MITM) attack.

Create a new composer.bat file alongside composer.phar:

C:\bin>echo @php "%~dp0composer.phar" %*>composer.bat

Close your current terminal. Test usage with a new terminal:

C:\Users\username>composer -V
Composer version 27d8904

Using Composer

We will now use Composer to install the dependencies of the project. If you don't have a composer.json file in the current directory please skip to the Basic Usage chapter.

To resolve and download dependencies, run the install command:

php composer.phar install

If you did a global install and do not have the phar in that directory run this instead:

composer install

Following the example above, this will download monolog into the vendor/monolog/monolog directory.

Note: Composer will attempt to protect all HTTPS requests using SSL/TLS. It implements peer verification using a certificate bundle, either one installed on the local system or a copy distributed with Composer. You may also pass the path to a bundle using the --cafile option for most commands. While you can also disable peer verification by passing the --disable-tls option, this is not recommended and will leave all downloads susceptible to Man-In-The-Middle (MITM) attacks.

Autoloading

Besides downloading the library, Composer also prepares an autoload file that's capable of autoloading all of the classes in any of the libraries that it downloads. To use it, just add the following line to your code's bootstrap process:

require 'vendor/autoload.php';

Woah! Now start using monolog! To keep learning more about Composer, keep reading the "Basic Usage" chapter.

Basic Usage →