1. 仅更新单个库
composer update foo/bar
2. 不编辑composer.json的情况下安装库
composer require "foo/bar:1.0.0"
3. 派生
composer create-project doctrine/orm path 2.2.0
http://www.phpcomposer.com/5-features-to-know-about-composer-php/
后面还有两条不太理解就没有摘抄过来了