xcode 11.3.1 已安装，执行

sudo gem install cocoapods

出现错误

RROR:  Error installing cocoapods:
         ERROR: Failed to build gem native extension.
 current directory: /Library/Ruby/Gems/2.3.0/gems/ffi-1.12.2/ext/ffi_c
 /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -r ./siteconf20200319-1090-1u4hxao.rb extconf.rb
 mkmf.rb can't find header files for ruby at /System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/lib/ruby/include/ruby.h
 extconf failed, exit code 1

执行下面的命令，安装后, 问题解决

open /Library/Developer/CommandLineTools/Packages/macOS_SDK_headers_for_macOS_10.14.pkg