printable.rb

#!/usr/bin/env ruby -Ku

require 'nkf'

class String
  def printable!
    self.each_char.find_all{|ch|  NKF.guess(ch) == NKF::UTF8}.join("")
  end
end

require 'test/unit'
class PrintableTest < Test::Unit::TestCase
  def test_printable
    assert_equal "あいえお", "あ\000い\343う\201え\202お".printable!
  end
end