Install ruby2.5-doc by entering the following commands in the terminal:
sudo apt update sudo apt install ruby2.5-doc
Description:
Documentation for Ruby 2.5
Ruby is the interpreted scripting language for quick and easy object-oriented programming. It has many features to process text files and to do system management tasks (as in perl). It is simple, straight-forward, and extensible. . This package contains the autogenerated documentation for Ruby 2.5.
Homepage: http://www.ruby-lang.org/
Version: 2.5.1-1ubuntu1
Section: doc