/usr/lib/ruby/1.9.1/tkmenubar.rb is in libtcltk-ruby1.9.1 1.9.3.484-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | #
# tkmenubar.rb - load tk/menubar.rb
#
require 'tk/menubar'
|