安装 - *nix
下载 Composer 的可执行文件
curl -sS https://getcomposer.org/installer | php
注意： 如果上述方法由于某些原因失败了，你还可以通过 php >下载安装器：
php -r "readfile('https://getcomposer.org/installer');" | php
这将检查一些 PHP 的设置，然后下载 composer.phar 到你的工作目录中。这是 Composer 的二进制文件。这是一个 PHAR 包（PHP 的归档），这是 PHP 的归档格式可以帮助用户在命令行中执行一些操作。
局部安装
你可以通过 --install-dir 选项指定 Composer 的安装目录（它可以是一个绝对或相对路径）：
php composer-setup.php --install-dir=bin --filename=composer
全局安装
你可以将此文件放在任何地方。如果你把它放在系统的 PATH 目录中，你就能在全局访问它。 在类Unix系统中，你甚至可以在使用时不加 php 前缀。
你可以执行这些命令让 composer 在你的系统中进行全局调用：
mv composer.phar /usr/local/bin/composer
现在只需要运行 composer 命令就可以使用 Composer 而不需要输入 php composer.phar。
[elastic@iZm5ebjvditkx9x8pm3dw4Z bin]$ composer
______
/ ____/___ ____ ___ ____ ____ ________ _____
/ / / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/
/ /___/ /_/ / / / / / / /_/ / /_/ (__ ) __/ /
\____/\____/_/ /_/ /_/ .___/\____/____/\___/_/
/_/
Composer version 1.5.1 2017-08-09 16:07:22
Usage:
command [options] [arguments]
Options:
-h, --help Display this help message
-q, --quiet Do not output any message
-V, --version Display this application version
--ansi Force ANSI output
--no-ansi Disable ANSI output
-n, --no-interaction Do not ask any interactive question
--profile Display timing and memory usage information
--no-plugins Whether to disable plugins.
-d, --working-dir=WORKING-DIR If specified, use the given directory as working directory.
-v|vv|vvv, --verbose Increase the verbosity of messages: 1 for normal output, 2 for more verbose output and 3 for debug
Available commands:
about Shows the short information about Composer.
archive Creates an archive of this composer package.
browse Opens the package's repository URL or homepage in your browser.
clear-cache Clears composer's internal package cache.
clearcache Clears composer's internal package cache.
config Sets config options.
create-project Creates new project from a package into given directory.
depends Shows which packages cause the given package to be installed.
diagnose Diagnoses the system to identify common errors.
dump-autoload Dumps the autoloader.
dumpautoload Dumps the autoloader.
exec Executes a vendored binary/script.
global Allows running commands in the global composer dir ($COMPOSER_HOME).
help Displays help for a command
home Opens the package's repository URL or homepage in your browser.
info Shows information about packages.
init Creates a basic composer.json file in current directory.
install Installs the project dependencies from the composer.lock file if present, or falls back on the composer.json.
licenses Shows information about licenses of dependencies.
list Lists commands
outdated Shows a list of installed packages that have updates available, including their latest version.
prohibits Shows which packages prevent the given package from being installed.
remove Removes a package from the require or require-dev.
require Adds required packages to your composer.json and installs them.
run-script Runs the scripts defined in composer.json.
search Searches for packages.
self-update Updates composer.phar to the latest version.
selfupdate Updates composer.phar to the latest version.
show Shows information about packages.
status Shows a list of locally modified packages.
suggests Shows package suggestions.
update Updates your dependencies to the latest version according to composer.json, and updates the composer.lock file.
validate Validates a composer.json and composer.lock.
why Shows which packages cause the given package to be installed.
why-not Shows which packages prevent the given package from being installed.
[elastic@iZm5ebjvditkx9x8pm3dw4Z bin]$
修改镜像源地址：
为了提升下载安装包的速度，建议将composer的镜像源修改为国内的源：
官方推荐有两种使用方法，使用任意一种均可。
方法一： 修改 composer 的全局配置文件（推荐方式）
打开命令行窗口（windows用户）或控制台（Linux、Mac 用户）并执行如下命令：
composer config -g repo.packagist composer https://packagist.phpcomposer.com
方法二： 修改当前项目的 composer.json 配置文件：
打开命令行窗口（windows用户）或控制台（Linux、Mac 用户），进入你的项目的根目录（也就是 composer.json 文件所在目录），执行如下命令：
composer config repo.packagist composer https://packagist.phpcomposer.com
上述命令将会在当前项目中的 composer.json 文件的末尾自动添加镜像的配置信息（你也可以自己手工添加）：
"repositories": {
"packagist": {
"type": "composer",
"url": "https://packagist.phpcomposer.com"
}
}
以 laravel 项目的 composer.json 配置文件为例，执行上述命令后如下所示（注意最后几行）：
{
"name": "laravel/laravel",
"description": "The Laravel Framework.",
"keywords": ["framework", "laravel"],
"license": "MIT",
"type": "project",
"require": {
"php": ">=5.5.9",
"laravel/framework": "5.2.*"
},
"config": {
"preferred-install": "dist"
},
"repositories": {
"packagist": {
"type": "composer",
"url": "https://packagist.phpcomposer.com"
}
}
}
OK，一切搞定！试一下 composer install 来体验飞一般的速度吧！
镜像原理：
一般情况下，安装包的数据（主要是 zip 文件）一般是从 github.com 上下载的，安装包的元数据是从 packagist.org 上下载的。
然而，由于众所周知的原因，国外的网站连接速度很慢，并且随时可能被“墙”甚至“不存在”。
“Packagist 中国全量镜像”所做的就是缓存所有安装包和元数据到国内的机房并通过国内的 CDN 进行加速，这样就不必再去向国外的网站发起请求，从而达到加速 composer install 以及 composer update 的过程，并且更加快速、稳定。因此，即使 packagist.org、github.com 发生故障（主要是连接速度太慢和被墙），你仍然可以下载、更新安装包。
修改composer地址参考文档： Packagist / Composer中国全量镜像
附：全局安装英文原文：
Globally#
You can place the Composer PHAR anywhere you wish. If you put it in a directory that is part of your PATH, you can access it globally. On unixy systems you can even make it executable and invoke it without directly using the php interpreter.
After running the installer following the Download page instructions you can run this to move composer.phar to a directory that is in your path:
mv composer.phar /usr/local/bin/composer
Note:
If the above fails due to permissions, you may need to run it again with sudo.
Note:
On some versions of OSX the/usrdirectory does not exist by default. If you receive the error "/usr/local/bin/composer: No such file or directory" then you must create the directory manually before proceeding:mkdir -p /usr/local/bin.
Note:
For information on changing your PATH, please read the Wikipedia article and/or use Google.
Now just run composer in order to run Composer instead of php composer.phar.
