Could not open input file: composer.phar

Yii 2官网推荐用Composer安装框架，但是在本地出错：Could not open input file: composer.phar。后来修改了命令行就ok了，难道是我装的Composer跟官网的不同？

Yii官网推荐：php composer.phar global require "fxp/composer-asset-plugin:1.0.0"

正确的：composer global require "fxp/composer-asset-plugin:1.0.0"