## sass.rb

template = %q{
  body
    :background url(/images/<%= @file %>.jpg)
}.gsub(/^  /){}

## makesass.rb

require 'erb'

['f1','f2','f3'].each do |it|
  @file = it
  f = File.read("sass.rb")
  sass = File.new("#{it}.sass","w+")
  sass.puts ERB.new(eval(f)).result
end