89 lines
3.0 KiB
Markdown
89 lines
3.0 KiB
Markdown
# Introduction
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Composer is a tool for dependency management in PHP. It allows you to declare
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the dependent libraries your project needs and it will install them in your
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project for you.
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## Dependency management
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Composer is not a package manager. Yes, it deals with "packages" or libraries, but
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it manages them on a per-project basis, installing them in a directory (e.g. `vendor`)
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inside your project. By default it will never install anything globally. Thus,
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it is a dependency manager.
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This idea is not new and Composer is strongly inspired by node's [npm](http://npmjs.org/)
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and ruby's [bundler](http://gembundler.com/). But there has not been such a tool
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for PHP.
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The problem that composer solves is this:
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a) You have a project that depends on a number of libraries.
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b) Some of those libraries depend on other libraries .
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c) You declare the things you depend on
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d) Composer finds out which versions of which packages need to be installed, and
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install them (meaning it downloads them into your project).
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## Declaring dependencies
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Let's say you are creating a project, and you need a library that does logging.
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You decide to use [monolog](https://github.com/Seldaek/monolog). In order to
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add it to your project, all you need to do is create a `composer.json` file
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which describes the project's dependencies.
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{
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"require": {
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"monolog/monolog": "1.0.*"
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}
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}
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We are simply stating that our project requires some `monolog/monolog` package,
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any version beginning with `1.0`.
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## Installation
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### 1) Downloading the Composer Executable
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To actually get Composer, we need to do two things. The first one is installing
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composer (again, this mean downloading it into your project):
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$ curl -s http://getcomposer.org/installer | php
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This will just check a few PHP settings and then download `composer.phar` to
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your working directory. This file is the composer binary. It is a PHAR (PHP
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archive), which is an archive format for PHP which can be run on the command
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line, amongst other things.
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You can install composer to a specific directory by using the `--install-dir`
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option and providing a target directory (it can be an absolute or relative path):
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$ curl -s http://getcomposer.org/installer | php -- --install-dir=bin
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You can place this file anywhere you wish. If you put it in your `PATH`,
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you can access it globally. On unixy systems you can even make it
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executable and invoke it without `php`.
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### 2) Using Composer
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Next, run the command the `install` command to calculate and download dependencies:
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$ php composer.phar install
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This will download monolog into the `vendor/monolog/monolog` directory.
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## Autoloading
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Besides download the library, Composer also prepares an autoload file that's
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capable of autoloading all of the classes in any of the libraries that it
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downloads. To use it, just add the following line to your code's bootstrap
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process:
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require 'vendor/.composer/autoload.php';
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Woh! Now starting using monolog! To keep learning more about Composer, keep
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reading the "Basic Usage" chapter.
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[Basic Usage](01-basic-usage.md) →
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