Generate table of contents from Markdown file

toc.rb

#!/usr/bin/env ruby

# sanity checks
if ARGV.count == 0
  puts "You must provide a file name"
  return
elsif File.exist?(ARGV.first) == false
  puts "That file doesn't exist"
  return
end

toc = Array.new
toc << "## Table of Contents"

File.open(ARGV.first).each do |line|
  if line.start_with? "##"
    # count number of lines, figure out how many leading paces we need
    # four spaces for each hash after the second
    spaces = " " * (line.split(" ").first.count("#") - 2) * 4
    title = line.split(" ")
    title.shift
    # links are the title, downcased, and spaces replaced with hyphens
    link = title.map {|w| w.downcase } .join("-")
    toc << "#{spaces}* [#{title.join(" ")}](##{link})"
  end
end
puts toc.join("\n")

Easy way to use on OS X
./toc.rb <FILENAME> | pbcopy
Then paste wherever you please