Meta Code converts itself into a highlighted HTML or PDF document.

meta_code.rb

require "coderay"
require "pdfkit"
require File.join(File.dirname(__FILE__), "styles/tomorrow_night")

module Meta
  class Code
    attr_reader :creator

    def initialize(options = {})
      @creator = options[:creator]
    end

    def save(format)
      raise ArgumentError, "Invalid format: #{format}" unless %w(txt html pdf).include?(format.to_s)
      File.open("#{File.basename(__FILE__, ".rb")}.#{format}", "w") { |f| f.write(send(format)) }
    end

    def pdf
      @pdf ||= PDFKit.new(html, page_width: 150, page_height: 150, margin_top: 0, margin_right: 0,
        margin_bottom: 0, margin_left: 0).to_pdf
    end

    def html
      @html ||= CodeRay.encode(txt, :ruby, :page, style: :tomorrow_night, line_numbers: false)
    end

    def txt
      @txt ||= "#{credits}\n#{File.read(__FILE__)}"
    end

    protected

    def credits
      <<-RB.gsub(/^\s+/, "")
        # By #{creator}
        # Copyright #{Time.now.year}
      RB
    end
  end
end

Meta::Code.new(creator: "Sjoerd Andringa").save(ARGV[0] || :html)

tomorrow_night.rb

module CodeRay
module Styles

  # A colorful theme using CSS 3 colors (with alpha channel).
  class TomorrowNight < Style

    register_for :tomorrow_night

    code_background = '#1d1f21'
    numbers_background = 'hsl(180,65%,90%)'
    border_color = 'silver'
    normal_color = '#c5c8c6'

    CSS_MAIN_STYLES = <<-MAIN  # :nodoc:
body {
  background-color: #{code_background};
  padding: 7mm;
  margin: 0;
  min-height: 136mm;
}
.CodeRay {
  color: #{normal_color};
}
.CodeRay pre {
  margin: 0px;
  font-family: Monaco;
  font-size: 7pt;
  font-weight: normal !important;
  line-height: 1.2em;
}

span.CodeRay { white-space: pre; border: 0px; padding: 2px; }

table.CodeRay { border-collapse: collapse; width: 100%; padding: 2px; }
table.CodeRay td { padding: 2px 4px; vertical-align: top; }

.CodeRay .line-numbers {
  background-color: #{numbers_background};
  color: gray;
  text-align: right;
  -webkit-user-select: none;
  -moz-user-select: none;
  user-select: none;
}
.CodeRay .line-numbers a {
  background-color: #{numbers_background} !important;
  color: gray !important;
  text-decoration: none !important;
}
.CodeRay .line-numbers a:target { color: blue !important; }
.CodeRay .line-numbers .highlighted { color: red !important; }
.CodeRay .line-numbers .highlighted a { color: red !important; }
.CodeRay span.line-numbers { padding: 0px 4px; }
.CodeRay .line { display: block; float: left; width: 100%; }
.CodeRay .code { width: 100%; }
    MAIN

    TOKEN_COLORS = <<-'TOKENS'
.debug { color: white !important; background: blue !important; }

.annotation { color:#007 }
.attribute-name { color:#b48 }
.attribute-value { color:#700 }
.binary { color:#509 }
.char .content { color:#b5bd68 }
.char .delimiter { color:#b5bd68 }
.char { color:#b5bd68 }
.class { color:#f0c674;  }
.class-variable { color:#369 }
.color { color:#0A0 }
.comment { color:#969896 }
.comment .char { color:#969896 }
.comment .delimiter { color:#969896 }
.complex { color:#A08 }
.constant { color:#f0c674;  }
.decorator { color:#B0B }
.definition { color:#099;  }
.delimiter { color:b5bd68 }
.directive { color:#088;  }
.doc { color:#970 }
.doc-string { color:#D42;  }
.doctype { color:#34b }
.entity { color:#800;  }
.error { color:#F00; background-color:#FAA }
.escape  { color:#666 }
.exception { color:#C00;  }
.float { color:#60E }
.function { color:#81a2be;  }
.global-variable { color:#d70 }
.hex { color:#02b }
.imaginary { color:#f00 }
.include { color:#B44;  }
.inline { color: #b5bd68 }
.inline-delimiter { color: #de935f }
.instance-variable { color:#cc6666 }
.integer  { color:#de935f }
.key .char { color: #60f }
.key .delimiter { color: #404 }
.key { color: #606 }
.keyword { color:#b294bb;  }
.label { color:#970;  }
.local-variable { color:#963 }
.namespace { color:#707;  }
.octal { color:#40E }
.operator { }
.predefined { color:#369;  }
.predefined-constant { color:#de935f }
.predefined-type { color:#0a5;  }
.preprocessor { color:#579 }
.pseudo-class { color:#00C;  }
.regexp .content { color:#cc6666 }
.regexp .delimiter { color:#cc6666 }
.regexp .modifier { color:#cc6666 }
.regexp { }
.reserved { color:#080;  }
.shell .content { color:#2B2 }
.shell .delimiter { color:#161 }
.shell { background-color:hsla(120,100%,50%,0.06); }
.string .char { color: #b5bd68 }
.string .content { color: #b5bd68 }
.string .delimiter { color: #b5bd68 }
.string .modifier { color: #b5bd68 }
.string {  }
.symbol .content { color:#b5bd68 }
.symbol .delimiter { color:#b5bd68 }
.symbol { color:#b5bd68 }
.tag { color:#070 }
.type { color:#339;  }
.value { color: #088; }
.variable  { color:#037 }

.insert { background: hsla(120,100%,50%,0.12) }
.delete { background: hsla(0,100%,50%,0.12) }
.change { color: #bbf; background: #007; }
.head { color: #f8f; background: #505 }
.head .filename { color: white; }

.delete .eyecatcher { background-color: hsla(0,100%,50%,0.2); border: 1px solid hsla(0,100%,45%,0.5); margin: -1px; border-bottom: none; border-top-left-radius: 5px; border-top-right-radius: 5px; }
.insert .eyecatcher { background-color: hsla(120,100%,50%,0.2); border: 1px solid hsla(120,100%,25%,0.5); margin: -1px; border-top: none; border-bottom-left-radius: 5px; border-bottom-right-radius: 5px; }

.insert .insert { color: #0c0; background:transparent;  }
.delete .delete { color: #c00; background:transparent;  }
.change .change { color: #88f }
.head .head { color: #f4f }
    TOKENS

  end

end
end