redrug
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The redcarpet library can be a bit cumbersome to use, and redrug aims to rectify this problem by wrapping it with simpler interfaces for common use cases. Three places to get information about RedRug include:

Installation

The simple way to install redrug is to use the gem command:

  $ gem install redrug

You can also build from source and install it the "hard" way. To do this, first clone the sources to your local system using Fossil SCM:

  $ fossil clone http://redrug.fossrec.com redrug.fossil

Then, open the repository in an appropriate directory:

  $ mkdir redrug
  $ cd redrug
  $ fossil open ../redrug.fossil

Finally, build and install, where in this example the N.N.N sequence is a series of numbers indicating the current version number of the gem.

  $ gem build red_rug.gemspec
  $ gem install redrug-N.N.N.gem

Rails Usage

The most convenient use of RedRug with Rails is probably as an application helper. The following example assumes that approach.

First, stick it in your Gemfile:

  gem 'redrug'

Next, make sure you install it:

  $ bundle install

Finally (and this is the "hard" part, of course), set up a helper in your project's app/helpers/application_helper.rb (though if you are only going to use it in very limited contexts, you may want to stick it in some other helper within app/helpers/):

  # whatever other requires you need
  require 'red_rug'

  module ApplicationHelper
    # whatever other helper methods you've defined

    def markdown text
      RedRug.to_html(text).html_safe
    end
  end

You can then use it wherever you need to parse Markdown by executing the markdown method, most likely in views. For instance, there's always this common pattern, in (for instance) your app/views/profiles/show.html.erb view:

  <h2><%= @article.title %></h2>

  <%= markdown @article.body %>

Voila: Markdown enhanced blogging.

HTML Safety

Alas, the simplistic approach above may expose you to the dangers of unescaped HTML input from users. The following rewrite of the markdown helper method as two methods provides both a way to escape any HTML in the input Markdown text and a way to leave HTML unescaped when you trust the source of the Markdown text and want to allow HTML to pass through unmolested:

  module ApplicationHelper
    # whatever other helper methods you've defined

    # use this for input you do not trust
    def markdown text
      RedRug.to_html(h text).html_safe
    end

    # use this for input you trust, if you really really must
    def septic_markdown text
      RedRug.to_html(text).html_safe
    end
  end

Since RedRug version 0.3.0, you have another alternative that relies on Redcarpet's own HTML escaping capabilities. If you wish to use that instead of the Rails h helper, you can do this with the HTML-escaped version of your RedRug-based Markdown helper:

  module ApplicationHelper
    # . . .

    def markdown text
      RedRug.to_html(text, escape_html: true).html_safe
    end

    # . . .
  end

Library Usage

At this time, the RedRug module provides a very simple API for translating Markdown into HTML. The basic use case examples are as follows:

  require 'red_rug'

  RedRug.from_file '/path/to/filename.md'

  RedRug.to_html <<END
    # This Is A Markdown Heading

    This is how paragraphs look in Markdown.
  END

Command Line Usage

The redrug gem provides a redrug command line utility that takes a Markdown formatted file as input and translates it into HTML, dumping the results to standard output. The usual approach would be to use a redirect to send the output to a persistent file instead:

  $ redrug filename.md > filename.html

This translates the contents of a Markdown formatted file, filename.md, into HTML, then writes that HTML into a file called filename.html.

It can also accept Markdown from standard input, so commands such as the following examples should also work:

  $ cat file1.md file2.md file3.md | redrug > filename.html
  $ redrug < filename.md > filename.html

The usual Unix pipeline rules apply.

As of RedRug version 0.3.0, the redrug utility also accepts a command line option for escaping HTML before parsing Markdown:

  $ redrug -e filename.md

Simply put, -e employs Redcarpet's :html_escape parsing option to escape HTML before parsing any Markdown. Otherwise, the behavior of the redrug utility has not changed.

Bugs And Feature Requests

To file a bug report, feature request, or other issue, please log in as "anonymous" using the temporary password provided on the login page, then click the Tickets link and select New Ticket. Select the appropriate issue type before submitting.

Other

For more information, see either the redrug project page or the redrug Rubygems page.