I have no experience with Ruby. When I try to do gem install nokogiri
on MacOS I am getting.
Building native extensions. This could take a while...
ERROR: Error installing nokogiri:
ERROR: Failed to build gem native extension.
current directory: /Library/Ruby/Gems/2.3.0/gems/nokogiri-1.10.5/ext/nokogiri
/System/Library/Frameworks/Ruby.framework/Versions/2.3/usr/bin/ruby -I /Library/Ruby/Site/2.3.0 -r ./siteconf20191105-81089-x3wjwy.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
Gem files will remain installed in /Library/Ruby/Gems/2.3.0/gems/nokogiri-1.10.5 for inspection.
Results logged to /Library/Ruby/Gems/2.3.0/extensions/universal-darwin-18/2.3.0/nokogiri-1.10.5/gem_make.out