A very basic script to translate a simple HTML file (consisting only of paragraphs with bold & italic text) to Markdown.

convert_to_markdown.rb

require 'nokogiri'
 
file = ARGV[0]
 
if !File.exist?(file)
  puts "File #{file} does not exist."
  exit
end

html = File.read(file)
 
puts 'Parsing HTML...'
document = Nokogiri::HTML.parse(html)
 
paragraphs = []
 
puts 'Reading content...'
document.css('p').each do |paragraph|
  # Skip blank paragraphs.
  if paragraph.content =~ /\A\s*\Z/
    next
  end
 
  paragraph.css('i').each do |italic|
    italic.replace "*#{italic.content}*"
  end
  paragraph.css('b').each do |bold|
    bold.replace "**#{bold.content}**"
  end

  # Replace newlines not at the beginning of a line. 
  paragraphs << paragraph.content.gsub(/(?<!^)\n/, ' ')
end
 
markdown_filename = File.join(File.dirname(file), File.basename(file, '.html') + '.md')
 
puts "Writing Markdown to #{markdown_filename}..."
File.open(markdown_filename, 'w') do |f|
  f.write(paragraphs.join("\n"))
end
 
puts "Done!"

This is useful if you have, e.g., a basic Word document with no frills—just some bold and/or italic text. Use Word, OpenOffice, etc. to export the file to HTML, then run this script to get Markdown.