Error using FSSM to monitor SASS files

I'm monitoring a theme folder in a WordPress project to watch .scss files and run them througg the command line sass tool to create clean .css files.

The script works in so much as it does the conversion put it fails to provide any output as it gets an 'FSSM callback error'. Can anybody tell me why this happens?

#sudo gem install fssm
#sudo gem install haml
# Script to watch a directory for any changes to an scss file and compile it to css in the same place
#
# USAGE: ruby sassy.rb <directory_to_watch>
#
require 'rubygems'
require 'fssm'

#directory = File.join(File.dirname(__FILE__), ARGV.first)
directory = "../wp-content/themes/"
FSSM.monitor(directory, '**/*.scss') do
  update do |base, relative|
    input = "#{base}/#{relative}"
    output = "#{base}/#{relative.gsub!('.scss', '.css')}"
    command = "sass --scss --watch #{input}:#{output}"
    %x{#{command}}

    puts "SASSy regenerated #{input} to #{output}"
  end
end

As I say the SCSS is compiled to a .css file in the same directory but the error is:

sy-mbp:_build simon$ ruby sassy.rb
^Csassy.rb:19:in ``': update - /Data/code/eil/wp-content/themes/eil-baseline/style.scss:  (FSSM::CallbackError)
    from sassy.rb:19
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/path.rb:73:in `call'
    from /Lib开发者_开发知识库rary/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/path.rb:73:in `run_callback'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/path.rb:55:in `callback_action'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/path.rb:35:in `update'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/state/directory.rb:38:in `modified'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/state/directory.rb:36:in `each'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/state/directory.rb:36:in `modified'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/state/directory.rb:17:in `refresh'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/fsevents.rb:15:in `add_handler'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/fsevents.rb:14:in `each'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/fsevents.rb:14:in `add_handler'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/rubycocoa/fsevents.rb:107:in `call'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/rubycocoa/fsevents.rb:107:in `initialize'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/fsevents.rb:27:in `call'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/fsevents.rb:27:in `CFRunLoopRun'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/backends/fsevents.rb:27:in `run'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm/monitor.rb:20:in `run'
    from /Library/Ruby/Gems/1.8/gems/fssm-0.2.3/lib/fssm.rb:18:in `monitor'
    from sassy.rb:12

Help greatly appreciated!

Simon

Rewrote it using watchr, which I've found is pretty simple to get rolling with. Save https://gist.github.com/919884 to watch_scss.rb, install the watchr gem and run watchr watch_scss.rb in a directory above wp-content.

With the current version of the sass gem, running

sass --watch ../wp-content/themes/

from the command line will handle looking for scss file changes and generating the css version

http://sass-lang.com/docs/yardoc/file.SASS_CHANGELOG.html#3-0-0-watch