This script takes simple Markdown lists and converts them for use in Bike

md_to_bike.rb

#!/usr/bin/env ruby
# frozen_string_literal: true

# This script takes simple Markdown lists and converts them for use in
# Bike (https://www.hogbaysoftware.com/bike/), a Mac outliner app from
# Hog Bay Software.
#
# It doesn't handle nested code blocks or any non-list Markdown. It just
# turns simple lists into text Bike will recognize when it's pasted into
# a Bike document. Multiple paragraphs in a list item become additional
# nodes at the same level.

require 'shellwords'
require 'fcntl'

stdin = $stdin.read.strip if $stdin.stat.size.positive? || $stdin.fcntl(Fcntl::F_GETFL, 0).zero?

if !stdin && ARGV.count != 1
  exe = File.basename(__FILE__)
  puts "#{exe} requires one argument"
  puts "#{exe} [markdown file]"
  Process.exit 1
end

source = ARGV[0]

# Read input file
content = stdin ? stdin : IO.read(source).strip
# Remove spaces from empty lines
content.gsub!(/^\s*\n/, "\n")
# Replace consecutive empty lines with a single newline
content.gsub!(/\n+/, "\n")

# Replace 2 or 4 spaces with tabs (based on detected indentation)
m = content.match(/^ {2,4}/) # find first indentation
indentation = m ? m[0].length : 1 # determine whether first indent is 2 or 4 spaces
content.gsub!(/^( {#{indentation}})+(?=\S)/) do |m| # Replace leading spaces with tabs
  mtch = Regexp.last_match(0)
  mtch ? "\t" * (mtch.length / indentation) : m # tab * detected indent / detected indentation
end

# Replace markdown list markers
content.gsub!(/(\s*)[+*\-] /, '\1')

# Copy result to clibpoard
`echo #{Shellwords.escape(content)} | pbcopy`

puts "Results in clipboard. Paste into a Bike document."