Simple example of unix style filter written in ruby. This one filters a dot file created by the rails-erd gem in order to put specializations in subgraphs.

edit_dot.rb

#!/usr/bin/env ruby

BEGIN {
  clusters = Hash.new {|h, k| h[k] = []}
}


ARGF.each_line do |line|
  case line
  when /\s*(\w+) -> .+?grey60/
    clusters[$1] << line
  when %r|\s*\}\s*|
  else
    puts line
  end
end

END {
  puts "graph [style=filled, color=aliceblue];"
  clusters.each do |name, edges|
    puts "subgraph cluster_#{name} {"
    puts "  label=#{name};"
    edges.each do |edge|
      puts "  #{edge}"
    end
    puts "}"
  end
  puts "}"
}