A quick-and-dirty CSS generator. Basically takes a file an does some text replacements, but allows you to use constants and blocks in your css.

example_config.yaml

--- 
:definitions: 
  MAIN_BG: white
  MAIN_TEXT_COLOR: black
  MAIN_LINK_COLOR: black
  MAIN_LINK_HIGHLIGHT_COLOR: "#FF0"

:partials: 
  MASTHEAD_GRADIENT: |
    background: rgb(40,40,40);
    background: -moz-linear-gradient(top, rgba(40,40,40,1) 0%, rgba(25,25,25,1) 100%);
    background: -webkit-gradient(linear, left top, left bottom, color-stop(0%,rgba(40,40,40,1)), color-stop(100%,rgba(25,25,25,1)));
    background: -webkit-linear-gradient(top, rgba(40,40,40,1) 0%,rgba(25,25,25,1) 100%);
    background: -o-linear-gradient(top, rgba(40,40,40,1) 0%,rgba(25,25,25,1) 100%);
    background: -ms-linear-gradient(top, rgba(40,40,40,1) 0%,rgba(25,25,25,1) 100%);
    background: linear-gradient(top, rgba(40,40,40,1) 0%,rgba(25,25,25,1) 100%);
    filter: progid:DXImageTransform.Microsoft.gradient( startColorstr='#282828', endColorstr='#191919',GradientType=0 );

example_style.css

.body {
   background: MAIN_BG;
   color: MAIN_TEXT_COLOR;
}

.masthead {
   <MASTHEAD_GRADIENT>
}

sgen.rb

#!/usr/bin/ruby
require 'yaml'

CONFIG_FILE = 'config.yaml'

if !File.exists? CONFIG_FILE
   IO.write(CONFIG_FILE, {
      :partials => { 'PARTIAL' => 'PARTIAL' },
      :definitions => { 'DEFINITION' => 'DEFINITION' }
   }.to_yaml)
   puts "No config file found, created `config.yaml`"
end

input_file = ARGV[0]
input_file ||= 'style.css'

output_file = ARGV[1]
output_file ||= File.join Dir.pwd, File.basename(input_file, '.css') + '-gen.css'

last_modified = {
   :css => nil,
   :config => nil
}

loop do
   current_modified = {
      :css => File.mtime(input_file),
      :config => File.mtime(CONFIG_FILE)
   }
   
   if last_modified != current_modified
      last_modified = current_modified
      
      css = IO.read input_file
      config = YAML.load_file CONFIG_FILE
      
      # Due to gsub order, partials can contain constants, and will
      # have them replaced correctly!
      config[:partials].each { |k,v| css.gsub! "<#{k}>", v }
      config[:definitions].each { |k,v| css.gsub! k, v }
      
      File.open(output_file, 'w') { |f| f.write css }
      puts "Update!"
   end
   sleep 0.2
end