Instead of opening up the Ruby Docs in a web page like this, we can use the
ri (Ruby Index) command-line tool to quickly lookup the documentation for a Ruby method, class or module.
ri File.open # View docs for method ri File # View docs for class ri Enumerable # View docs for module
Ruby is a very rich language with lots of built-in methods so being able to quickly look up the docs for its various methods saves a lot of time.
ri should be installed automatically when you install Ruby itself.