# File lib/rubygems/gem_commands.rb, line 1565
    def execute(io=STDOUT)
      if options[:list]
        version = options[:version] || "> 0.0.0"
        gem = get_one_gem_name
        
        s = options[:specdirs].map do |i|
          [i, File.join(i,"specifications")]
        end.flatten
        
        if s.empty?
          s = Gem::SourceIndex.installed_spec_directories
          path_kind = "default gem paths"
          system = true
        else
          path_kind = "specified path"
          system = false
        end

        si = Gem::SourceIndex.from_gems_in(*s)

        gem_spec = si.search(gem, version).last
        unless gem_spec
          io.puts "Unable to find gem '#{gem}' in #{path_kind}"
          if options[:verbose]
            io.puts "\nDirectories searched:"
            s.each do |p|
              io.puts p
            end
          end
          return
        end
        # show the list of files.
        gem_spec.files.each do |f|
          io.puts File.join(gem_spec.full_gem_path, f)
        end
      end
    end