Illustrates some of the shortcomings of Ruby's OptionParser class: it doesn't support required arguments out of the box and the design of the code that invokes the code block on "on" and "on_tail" methods requires binding to a variable to save options value, when this is really something that would be better achieved by passing the object into t…

option_parser_test.rb

#!/usr/bin/env ruby

# See http://stackoverflow.com/questions/1541294/how-do-you-specify-a-required-switch-not-argument-with-ruby-optionparser

require 'optparse'
require 'ostruct'
require 'pathname'

THIS_PATH = Pathname.new(__FILE__).realpath
THIS_DIR = THIS_PATH.dirname
THIS_BASE_NAME = THIS_PATH.basename

class MyOptionParser < OptionParser
  attr_reader :required_arg_names

  def initialize
    @required_arg_names = []
    super
  end

  def on_required(arg_sym, *args, &block)
    on *args, &block
    @required_arg_names << arg_sym
  end

  def on(*args, &block)
    super *args do |value|
      block.call(@options, value)
    end
  end

  def on_tail(*args, &block)
    super *args do
      block.call(@options)
    end
  end

  def run(args)
    @options = OpenStruct.new
    cloned_args = args.clone
    begin
      parse!(cloned_args)
    rescue OptionParser::InvalidOption, OptionParser::MissingArgument
      puts $!.to_s
      puts
      puts self
      exit 1
    end

    missing_arg_names = @required_arg_names.select { |arg_name| @options.send(arg_name).nil? }
    if !missing_arg_names.empty?
      puts "missing required option: #{missing_arg_names.join(', ')}"
      puts
      puts self
      exit 1
    end

    [@options, cloned_args]
  end
end

option_parser = MyOptionParser.new do |parser|
  parser.banner = "Usage: #{THIS_BASE_NAME} [options]"

  parser.on_required(:merge_version, '--merge-version MERGE-VERSION', 'Specify merge version') do |options, value|
    options.merge_version = value
  end

  parser.on_tail '-h', '--help', 'Show help' do
    puts parser
    exit
  end

  parser.on_tail '--version', 'Show version' do
    puts OptionParser::Version.join('.')
    exit
  end
end

options, free_args = option_parser.run(ARGV)
p options
p free_args