markdown.rb

require 'rubygems'
require 'redcarpet'
require 'pathname'

path = Pathname.new(ARGV.shift)

raise "Input path must be absolute." unless path.absolute?
raise "Input path must point to a file that exists" unless path.exist?
raise "Input path must point to a file that is readable" unless path.readable?

output   = Pathname.new(path.dirname.join(path.basename.sub(".md", ".html")))
engine   = Redcarpet::Markdown.new(Redcarpet::Render::HTML, :autolink => true, :space_after_headers => true)
document = engine.render(path.read)

output.open("w") { |f| f.write(document) }