$ ruby gl_tail-0.02.rb 
/usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `gem_original_require': no such file to load -- opengl (LoadError)
	from /usr/lib/ruby/site_ruby/1.8/rubygems/custom_require.rb:27:in `require'
	from gl_tail-0.02.rb:4