DouKaku?

require 'rubygems'
require 'win32/ipc' # http://rubyforge.org/projects/win32utils
require 'win32/changenotify' # http://rubyforge.org/projects/win32utils
include Win32

exit if ARGV == []
filename = File.expand_path(ARGV[0])

flags = ChangeNotify::FILE_NAME | ChangeNotify::LAST_WRITE | ChangeNotify::SIZE
cn = ChangeNotify.new(File.dirname(filename), false, flags)

loop {
  cn.wait(){|sa|
    sa.each {|st|
      puts "modified!" if st.file_name == File.basename(filename)
    }
  }
}