Never trust a board that clips things.

$ gem install evil_clipboard

You can listen for changes on the system's keyboard.

require "evil_clipboard"

EvilClipboard.listen do |clipboard_data|
  # do something with it
  puts clipboard_data
end

You can also continously inject data into the system's keyboard.

EvilClipboard.inject("Anything you want.")

The gem is available as open source under the terms of the MIT License.