在Mac上安装cocoapods遇到路径未被允许的情况

用命令：sudo gem install -n /usr/local/bin cocoapods

安装cocoapods  提示错误：

ERROR:  While executing gem ... (Gem::FilePermissionError)

You don't have write permissions for the /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/lib/ruby/gems/2.6.0 directory.

提示错误路径未被允许，然后我安装了rbenv ，安装完后再去执行就OK了，为什么出现这种情况，找时间看看！

如何安装rbenv 看这这篇文章https://www.jianshu.com/p/519e41f91b1a