codegolf_checker.rb

require 'tempfile'
def codegolf_check file, samples: nil
  unless samples
    samples = DATA.read.split(/^# ?input\n/).drop(1).map { |s| s.split(/# ?output\n/) }
  end
  lines = File.read(file).lines
  codes = []
  lines.each.with_index(1).each do |line, num|
    next unless /^# ?code ?(?<name>.*)$/ =~ line
    code = ''
    (num...lines.size).each do |i|
      break if lines[i] =~ /^(# ?code|)$/
      code << lines[i]
    end
    code.chomp! unless code =~ /\A#! ruby.+\n\z/
    codes << { code: code, name: (name.empty? ? "LINE#{num}" : "#{name}(#{num})") }
  end
  codes.group_by { |c| c[:code] }.select { |k, v| v.size >= 2 }.each do |k, v|
    puts "duplicate code in #{v.map { |c| c[:name] }}"
  end
  shortest = nil
  codes.each do |c|
    file = Tempfile.new ['code', 'rb']
    file.write c[:code]
    file.close
    result = samples.map.with_index(1) do |(sample_input, sample_output), number|
      output = IO.popen ['ruby', file.path], 'r+' do |io|
        io.write sample_input
        io.close_write
        io.read
      end
      if sample_output.chomp == output.chomp
        true
      else
        puts "#{c[:name]} \e[31mX(input#{number})\e[m"
        puts "\e[37m--expected--\e[m"
        puts sample_output
        puts "\e[37m---output---\e[m"
        puts output
        puts "\e[37m------------\e[m"
        false
      end
    end
    if result.all?
      puts "#{c[:name]} \e[32mO(#{c[:code].bytesize}B)\e[m"
      shortest = c if shortest.nil? || c[:code].bytesize < shortest[:code].bytesize
    end
  end

  if shortest
    puts "\e[1mShortest: #{shortest[:name]} #{shortest[:code].bytesize}B\e[m"
    puts shortest[:code]
  end
  exit
end

codegolf_checker_sample.rb

require './codegolf_checker'
codegolf_check __FILE__

# code
#! ruby -penguin

# code
loop { $> << ($<.getc || break) }

# code foo
Kernel.itself.puts Kernel.itself.gets

# code
$> << 5.times.map { $<.getc } * ''

__END__
#input
Hello
#output
Hello
#input
World!
#output
World!

output

LINE4 O(17B)
LINE7 O(33B)
foo(10) O(37B)
LINE13 X(input2)
--expected--
World!
---output---
World
------------
Shortest: LINE4 17B
#! ruby -penguin