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

sudo gem install -n /usr/local/bin cocoapods

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.

解决办法：

1.删除CocoaPods;

2.用命令"which -a ruby"，查看只有一个系统自带的ruby目录。

执行 which -a ruby 回车

/usr/bin/ruby

需要自己再安装一个最新版本的ruby:

解决：重新安装Ruby再安装其他命令即可

brew install ruby

安装完后检查，发现还是只有一个系统目录：

执行 which -a ruby 回车

/usr/bin/ruby

这时需要把新版本加到环境变量中： 

执行 which -a ruby 回车

/usr/bin/ruby

echo 'export PATH="/usr/local/opt/ruby/bin:$PATH"' >> ~/.zshrc
source ~/.zshrc
 
which -a ruby  
/usr/local/opt/ruby/bin/ruby
/usr/bin/ruby

3. 安装CocoaPods:

sudo gem install -n /usr/local/bin cocoapods