/usr/lib/ruby/2.0.0/tkextlib/tclx.rb is in ruby2.0-tcltk 2.0.0.484-1ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 | #
# TclX support
# by Hidetoshi NAGAI (nagai@ai.kyutech.ac.jp)
#
# call setup script for general 'tkextlib' libraries
require 'tkextlib/setup.rb'
# call setup script
require 'tkextlib/tclx/setup.rb'
# load library
require 'tkextlib/tclx/tclx'
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