class Gem::Commands::WhichCommand

def find_paths(package_name, dirs)
  result = []
  dirs.each do |dir|
    Gem.suffixes.each do |ext|
      full_path = File.join dir, "#{package_name}#{ext}"
      if File.exist? full_path and not File.directory? full_path then
        result << full_path
        return result unless options[:show_all]
      end
    end
  end
  result
end