Generate a Gemfile.

$ bundle init [OPTIONS]
  • Gemfile result. 
      # frozen_string_literal: true

  source "https://rubygems.org"

  git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }

  # gem "rails"

Note the file is only readable, you change the permissions first.

$ chmod +w Gemfile
$ nano Gemfile