Homebrew官网：http://brew.sh
Homebrew installs the stuff you need that Apple didn't
Homebrew的安装非常简单，打开终端复制、粘贴以下命令。
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
2.如果你当前的环境变量还没有加入 mongod ,手动添加的环境变量中.
$ nano ~/.bash_profile
//添加mongodb安装目录到环境变量中
export PATH=/usr/local/Cellar/mongodb/3.4.0/bin/:$PATH
3.如果让环境变量马上生效? 执行下面的
shell source ~/.bash_profile
