实现 Markdown 语法和代码语法高亮分别是用的 Redcarpet 和 pygments.rb 两个 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中添加如下两行：
gem 'redcarpet' gem 'pygments.rb'
需要说明的是，pygments.rb 依赖于 Python，所以确保机器已经安装了 Python 2.x。
然后在/app/controllers/comments_controller.rb中添加相应 redcarpet 和 pygments.rb 的代码：
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
end
end
最后在 View 中就可以直接调用 markdown 方法来处理博客正文了：
%= markdown @post.content %>
语法规则类似 Github 上的 Markdown，码字效率大大提高。
