Make UML diagrams from a PlantUML script embedded in Markdown

plantuml.rb

require 'pp'
require 'fileutils'

file = ARGV[0]
dirname = File.basename(file,'.*')
FileUtils.mkdir_p dirname
source = File.read(file)
i = 1

source.gsub(/(?<=<!---).+?(?=--->)/m) do |m|
  name = "#{dirname}/#{i}.txt"
  outpath = nil
  code = m.split("\n")[1..-1]
  code[0].gsub!(/@startuml\{([^{]+)\}/) do
    outname = "#{i}_#{$1}"
    outpath = "#{dirname}/#{outname}"
    "@startuml{#{outname}}"
  end
  code = code.join("\n")
  code = code.gsub(/\\>/,'>')
  
  old_code = File.read(name) rescue nil
  
  if old_code.nil? || code != old_code then
    File.write(name, code)
    system "plantuml #{name} && open #{outpath}"
  end
  
  i+=1
end