在执行pod 操作时提示一下错误，或者在安装pod时提示
Ignoring ffi-1.15.5 because its extensions are not built. Try: gem pristine ffi --version 1.15.5
根据后面的提示前面添加sudo
sudo gem pristine ffi --version 1.15.5
正常输出：
Ignoring ffi-1.15.5 because its extensions are not built. Try: gem pristine ffi --version 1.15.5
Restoring gems to pristine condition...
Building native extensions. This could take a while...
Restored ffi-1.15.5
如果出现：
Ignoring ffi-1.15.5 because its extensions are not built. Try: gem pristine ffi --version 1.15.5
ERROR: While executing gem ... (Gem::FilePermissionError)
You don't have write permissions for the /Library/Ruby/Gems/2.6.0 directory.
可以根据下面地址更改系统的权限
https://blog.csdn.net/SharkToping/article/details/79464581
更改后权限后
sudo gem update --system
根据提示输入密码,提示类似的内容。
Ignoring ffi-1.15.5 because its extensions are not built. Try: gem pristine ffi --version 1.15.5
Latest version already installed. Done.
再次执行，出现最开始提到的内容，在尝试执行pod命令
sudo gem pristine ffi --version 1.15.5
