安装haml时出错

Question

我只是想学习haml所以首先使用我的终端安装ruby 这是我安装的ruby版本：ruby 2.0.0p451 (2014-02-24 revision 45167) [universal.x86_64-darwin13]

当我运行此命令时：gem install haml 我收到这个错误：

MacBook-Pro:~ user$ gem install haml
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.0.0 directory.

谁能告诉我哪里出错？