What is ":require=>false:" in Gemfile?

It means that you will install the gem, but you will not require it when you start the Bundler.

If you're going to use a library,

require "whenever"

in writing.

To download a gem named whenever but require whereever

gem "whenever", :require=>"whereever"

I'm writing. If the name of the gem and the name of the libraay to require are different, write it like this