$schemamarkup = get_post_meta(get_the_ID(), 'schemamarkup', true); if(!empty($schemamarkup)) { echo $schemamarkup; }

Linux Mint 19 Can’t Find Header Files for Ruby At /usr/lib/ruby/include/ruby.h

August 6, 2018 | By the+gnu+linux+evangelist.

Linux Mint 19.x Tara/Tessa/Tina/Tricia can’t find header files for ruby

This Tip shows you How to Solve Linux Mint 19.x Tara/Tessa/Tina/Tricia can’t find header files for ruby at /usr/lib/ruby/include/ruby.h Issue.

And this Issue in Installing Ruby Gems is due to Missing Development Files on Linux Mint System.

Linux Mint 19.x Tara/Tessa/Tina/Tricia can't find header files for ruby at /usr/lib/ruby/include/ruby.h - Featured
sudo apt install ruby-dev

Or if you have Enabled the Ruby PPA:

sudo apt install ruby2.[x]-dev