UPD：

假设你有一个my_gem gem项目，里面有/templates文件夹：

# in my_gem.rb 

module MyGem
  def self.setup_files(project_root)
    File.write(File.join(project_root, 'my_gem.txt'), 'The content of file')
    # or
    FileUtils.cp_r("#{__dir__}/templates/", project_root)
  end
end

# in your project

require 'my_gem'
MyGem.setup_files(Dir.pwd)

# or in Rails project
MyGem.setup_files(Rails.root)

字符串