Installing cocoapods on macOS Mojave

I have looked through a lot of these questions and none seem to apply. I am trying to install cocoapods and run pod init in my xcode project. When I run sudo gem install cocoa podsI get right the end and see this:

Building native extensions. This could take a while...
ERROR:  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 -I /Library/Ruby/Site/2.3.0 -r ./siteconf20200314-453-8td9mi.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/ffi-1.12.2 for inspection.

And of course when I run pod init inside my Xcode project I get:

-bash: pod: command not found