gem install - fatal error: 'ruby/config.h' file not found in Catalina

记录一下安装cocoapods失败的问题。
新电脑，好久没用cocoapods了，新用到了一个库需要装一下cocoapods，结果
sudo gem install cocoapods
的时候报错了，错误就是标题那样的：

In file included from /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby.h:33:
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX11.1.sdk/System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/include/ruby-2.6.0/ruby/ruby.h:24:10: fatal error: 'ruby/config.h' file not found

OK，既然问题来了，那就search吧，在这里找到了答案：

image.png

也就是用xcrun工具安装：xcrun gem install cocoapods，原因截图里也说明了。
但是直接这么run有可能会报这个错：

ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /Library/Ruby/Gems/2.6.0 directory.

所以加上sudo就行：sudo xcrun gem install cocoapods

总结

搜索大法好！