rdoc2md.rb

require 'rdoc'
converter = RDoc::Markup::ToMarkdown.new
filename = ARGV[0] || 'README.rdoc'
rdoc = File.read(filename)
md = converter.convert(rdoc)
filename_raw = filename.split('.')[0]
File.open("#{filename_raw}.md", 'w') { |file| file.write(md) }

# ruby rdoc2md.rb >> README.md
# ruby rdoc2md.rb ABC.rdoc >> abc.md

rdoc2md.sh

alias rdoc2md='ruby ./rdoc2md.rb $1'

# rdoc2md >> README.md
# rdoc2md ABC.rdoc >> ABC.md