Composer 需要PHP5.3.2+ 以上的环境来运行。有几个敏感的PHP设置和编译标志也是必需的，但安装程序会发出警告当存在任何不兼容的情况。
比如PHP的扩展的要求是，安装或重新编译php without –disable-phar
为了从源地址安装软件包，而不是简单的压缩文件包，您将需要安装软件包的版本控制工具，比如git、svn或hg等。
Composer 是兼容多平台的，其运行适用于Windows，Linux和OSX。
安装失败的错误消息：
curl -sS https://getcomposer.org/installer | PHP #!/usr/bin/env php some settings on your machine make Composer unable to work properly. Make sure that you fix the issues listed below and run this script again: The phar extension is missing. Install it or recompile php without –disable-phar Your PHP (5.2.9) is too old, you must upgrade to PHP 5.3.2 or higher.
我的本地默认开发环境是PHP 5.2.9，当我尝试在PHP 5.2.9上安装时，提示版本过低，需要升级到PHP 5.3.2 或者更高的版本。
于是我下载XAMPP 1.7.7 usb lite 版本。
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_177\php\php.exe -v PHP 5.3.8 (cli) (built: Aug 23 2011 11:50:20) Copyright (c) 1997-2011 The PHP Group Zend Engine v2.3.0, Copyright (c) 1998-2011 Zend Technologies
XAMPP 1.7.7 下的PHP环境是5.3.8。确认我的PHP环境大于等于PHP5.3.2后。
PHP 5.3 安装 Composer
E:\USB\Dropbox\phpstorm\php53>curl -sS https://getcomposer.org/installer | E:\USB\xampp_177\php\php.exe #!/usr/bin/env php Some settings on your machine may cause stability issues with Composer. If you encounter issues, try to change the following: The openssl extension is missing, which will reduce the security and stability o f Composer. If possible you should enable it or recompile php with –with-openssl Downloading… Composer successfully installed to: E:\USB\Dropbox\phpstorm\php53\composer.phar Use it: php composer.phar
注意：
我关闭了XAMPP 1.7.7 Apache的SSL模块，所以Composer提示我警告，为了安全因素建议我开启SSL模块。不开启也不影响使用。
安装时的参数 | PHP，一定要更改为真实的PHP环境路径，比如 | E:\USB\xampp_177\php\php.exe
使用Composer为PHP路径 + 命令，在我们安装的环境中，使用方法为：E:\USB\xampp_177\php/php.exe composer.phar 命令。
我安装的环境是在Windows下，如果在Linux下，而PHP 5.3 环境也不在默认PHP命令下时，应该采用 | /usr/php/53/usr/bin/php，例如：
curl -sS https://getcomposer.org/installer | /usr/php/53/usr/bin/php
安装完成后，检查安装版本。
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_177\php/php.exe composer.phar -V Composer version 0209bd31a0ac3aeb2a68fc81e2d03c71072bef33
检查PHP Composer命令：
E:\USB\Dropbox\phpstorm\php53>E:\USB\xampp_177\php/php.exe composer.phar ______ / ____/___ ____ ___ ____ ____ ________ _____ / / / __ \/ __ `__ \/ __ \/ __ \/ ___/ _ \/ ___/ / /___/ /_/ / / / / / / /_/ / /_/ (__ ) __/ / \____/\____/_/ /_/ /_/ .___/\____/____/\___/_/ /_/ Composer version 0209bd31a0ac3aeb2a68fc81e2d03c71072bef33 Usage: [options] command [arguments] Options: –help -h Display this help message. –quiet -q Do not output any message. –verbose -v Increase verbosity of messages. –version -V Display this application version. –ansi Force ANSI output. –no-ansi Disable ANSI output. –no-interaction -n Do not ask any interactive question. –profile Display timing and memory usage information –working-dir -d If specified, use the given directory as working directory . Available commands: about Short information about Composer archive Create an archive of this composer package config Set config options create-project Create new project from a package into given directory. depends Shows which packages depend on the given package diagnose Diagnoses the system to identify common errors. dump-autoload Dumps the autoloader dumpautoload Dumps the autoloader help Displays help for a command 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. list Lists commands require Adds required packages to your composer.json and installs the m run-script Run the scripts defined in composer.json. search Search for packages self-update Updates composer.phar to the latest version. selfupdate Updates composer.phar to the latest version. show Show information about packages status Show a list of locally modified packages update Updates your dependencies to the latest version according to composer.json, and updates the composer.lock file. validate Validates a composer.json
这样我们在PHP5.3环境下的Composer已经安装完成。
类似的方法我们也可以安装PHP 5.4的环境上。
PHP 5.4 安装 Composer
下载XAMPP 1.8.1 usb lite 版本，将得到PHP5.4.7环境。