實現 Markdown 語法和代碼語法高亮分別是用的 Redcarpet 和 pygments.rb 兩個 Gem：

    https://github.com/vmg/redcarpet
    https://github.com/tmm1/pygments.rb
    https://github.com/richleland/pygments-css
    http://pygments.org/docs/lexers/

在/Gemfile中添加如下兩行：

gem 'redcarpet'gem 'pygments.rb'

需要說明的是，pygments.rb 依賴于 Python，所以確保機器已經安裝了 Python 2.x。

然后在/app/controllers/comments_controller.rb中添加相應 redcarpet 和 pygments.rb 的代碼：

class ApplicationController < ActionController::Base # Prevent CSRF attacks by raising an exception. # For APIs, you may want to use :null_session instead. protect_from_forgery with: :exception helper_method [:markdown] # Highlight code with Pygments class HTMLwithPygments < Redcarpet::Render::HTML  def block_code(code, language)   language = "text" if language.blank?   sha = Digest::SHA1.hexdigest(code)   Rails.cache.fetch ["code", language, sha].join("-") do    Pygments.highlight(code, :lexer => language)   end  end end protected # Markdown with Redcarpet def markdown(text)  renderer = HTMLwithPygments.new({   :filter_html => true,   :hard_wrap => true,   :link_attributes => {:rel => 'external nofollow'}  })  options = {   :autolink => true,   :no_intra_emphasis => true,   :fenced_code_blocks => true,   :lax_html_blocks => true,   :strikethrough => true,   :superscript => true,   :tables => true  }  Redcarpet::Markdown.new(renderer, options).render(text).html_safe endend

最后在 View 中就可以直接調用 markdown 方法來處理博客正文了：

<%= markdown @post.content %>

語法規則類似 Github 上的 Markdown，碼字效率大大提高。