[ruby] How to find where gem files are installed

You can trick gem open into displaying the gem path:

VISUAL=echo gem open gem-name

Example:

VISUAL=echo gem open rails
=> /usr/local/opt/asdf/installs/ruby/2.4.3/lib/ruby/gems/2.4.0/gems/rails-5.1.4

It just works, and no third party gem is necessary.