Redcarpet 2 is written with sugar, spice and everything nice

Redcarpet is Ruby library for Markdown processing that smells like butterflies and popcorn.

Redcarpet used to be a drop-in replacement for Redcloth. This is no longer the case since version 2 -- it now has its own API, but retains the old name. Yes, that does mean that Redcarpet 2 is not backwards-compatible with the 1.X versions.

Redcarpet is powered by the Sundown library. You might want to find out more about Sundown to see what makes this Ruby library so awesome.

This library is written by people

Redcarpet 2 has been rewritten from scratch by Vicent Martí (@vmg). Why are you not following me on Twitter?

Redcarpet would not be possible without the Sundown library and its authors (Natacha Porté, Vicent Martí, and its many awesome contributors).

You can totally install it as a Gem

Redcarpet is readily available as a Ruby gem. It will build some native extensions, but the parser is standalone and requires no installed libraries.

$ [sudo] gem install redcarpet

The Redcarpet source (including Sundown as a submodule) is available at GitHub:

$ git clone git://github.com/vmg/redcarpet.git

And it's like really simple to use

The core of the Redcarpet library is the Redcarpet::Markdown class. Each instance of the class is attached to a Renderer object; the Markdown class performs parsing of a document and uses the attached renderer to generate output.

The Markdown object is encouraged to be instantiated once with the required settings, and reused between parses.

Markdown.new(renderer, extensions={})

Initializes a Markdown parser

renderer -  a renderer object, inheriting from Redcarpet::Render::Base.
            If the given object has not been instantiated, the library
            will do it with default arguments.

extensions - a hash containing the Markdown extensions which the parser
            will identify. The following extensions are accepted:

            :no_intra_emphasis - do not parse emphasis inside of words.
                Strings such as `foo_bar_baz` will not generate `<em>`
                tags.

            :tables - parse tables, PHP-Markdown style

            :fenced_code_blocks - parse fenced code blocks, PHP-Markdown
                style. Blocks delimited with 3 or more `~` or backticks
                will be considered as code, without the need to be
                indented. An optional language name may be added at the
                end of the opening fence for the code block

            :autolink - parse links even when they are not enclosed in
                `<>` characters. Autolinks for the http, https and ftp
                protocols will be automatically detected. Email addresses
                are also handled, and http links without protocol, but
                starting with `www.`

            :strikethrough - parse strikethrough, PHP-Markdown style
                Two `~` characters mark the start of a strikethrough,
                e.g. `this is ~~good~~ bad`

            :lax_spacing - HTML blocks do not require to be surrounded
                by an empty line as in the Markdown standard.

            :space_after_headers - A space is always required between the
                hash at the beginning of a header and its name, e.g.
                `#this is my header` would not be a valid header.

            :superscript - parse superscripts after the `^` character;
                contiguous superscripts are nested together, and complex
                values can be enclosed in parenthesis,
                e.g. `this is the 2^(nd) time`

Example:

    markdown = Redcarpet::Markdown.new(Redcarpet::Render::HTML,
        :autolink => true, :space_after_headers => true)

Rendering with the Markdown object is done through Markdown#render. Unlike in the RedCloth API, the text to render is passed as an argument and not stored inside the Markdown instance, to encourage reusability.

Markdown#render(text)

Render a Markdown document with the attached renderer

text - a Markdown document

Example:

    markdown.render("This is *bongos*, indeed.")
    #=> "<p>This is <em>bongos</em>, indeed</p>"

Darling, I packed you a couple renderers for lunch

Redcarpet comes with two built-in renderers, Redcarpet::Render::HTML and Redcarpet::Render::XHTML, which output HTML and XHTML, respectively. These renderers are actually implemented in C, and hence offer a brilliant performance, several degrees of magnitude faster than other Ruby Markdown solutions.

All the rendering flags that previously applied only to HTML output have now been moved to the Render::HTML class, and may be enabled when instantiating the renderer:

Render::HTML.new(render_options={})

Initializes an HTML renderer. The following flags are available:

:filter_html - do not allow any user-inputted HTML in the output

:no_images - do not generate any `<img>` tags

:no_links - do not generate any `<a>` tags

:no_styles - do not generate any `<style>` tags

:safe_links_only - only generate links for protocols which are considered safe

:with_toc_data - add HTML anchors to each header in the output HTML,
    to allow linking to each section.

:hard_wrap - insert HTML `<br>` tags inside on paragraphs where the origin
    Markdown document had newlines (by default, Markdown ignores these
    newlines).

:xhtml - output XHTML-conformant tags. This option is always enabled in the
    `Render::XHTML` renderer.

    :link_attributes - hash of extra attributes to add to links

Example:

rndr = Redcarpet::Render::HTML.new(:no_links => true, :hard_wrap => true)

The HTML renderer has an alternate version, Redcarpet::Render::HTML_TOC, which will output a table of contents in HTML based on the headers of the Markdown document.

Furthermore, the abstract base class Redcarpet::Render::Base can be used to write a custom renderer purely in Ruby, or extending an existing renderer. See the following section for more information.

And you can even cook your own

Custom renderers are created by inheriting from an existing renderer. The built-in renderers, HTML and XHTML may be extended as such:

# create a custom renderer that allows highlighting of code blocks
class HTMLwithAlbino < Redcarpet::Render::HTML
  def block_code(code, language)
    Albino.safe_colorize(code, language)
  end
end

markdown = Redcarpet::Markdown.new(HTMLwithAlbino, :fenced_code_blocks => true)

But new renderers can also be created from scratch (see lib/render_man.rb for an example implementation of a Manpage renderer)

class ManPage < Redcarpet::Render::Base
    # you get the drill -- keep going from here
end

The following instance methods may be implemented by the renderer:

# Block-level calls
# If the return value of the method is `nil`, the block
# will be skipped.
# If the method for a document element is not implemented,
# the block will be skipped.
# 
# Example:
#
#   class RenderWithoutCode < Redcarpet::Render::HTML
#     def block_code(code, language)
#       nil
#     end
#   end
#
block_code(code, language)
block_quote(quote)
block_html(raw_html)
header(text, header_level)
hrule()
list(contents, list_type)
list_item(text, list_type)
paragraph(text)
table(header, body)
table_row(content)
table_cell(content, alignment)

# Span-level calls
# A return value of `nil` will not output any data
# If the method for a document element is not implemented,
# the contents of the span will be copied verbatim
autolink(link, link_type)
codespan(code)
double_emphasis(text)
emphasis(text)
image(link, title, alt_text)
linebreak()
link(link, title, content)
raw_html(raw_html)
triple_emphasis(text)
strikethrough(text)
superscript(text)

# Low level rendering
entity(text)
normal_text(text)

# Header of the document
# Rendered before any another elements
doc_header()

# Footer of the document
# Rendered after all the other elements
doc_footer()

# Pre/post-process
# Special callback: preprocess or postprocess the whole
# document before or after the rendering process begins
preprocess(full_document)
postprocess(full_document)

You can look at "How to extend the Redcarpet 2 Markdown library?" for some more explanations.

Also, now our Pants are much smarter

Redcarpet 2 comes with a standalone SmartyPants implementation. It is fully compliant with the original implementation. It is the fastest SmartyPants parser there is, with a difference of several orders of magnitude.

The SmartyPants parser can be found in Redcarpet::Render::SmartyPants. It has been implemented as a module, so it can be used standalone or as a mixin.

When mixed with a Renderer class, it will override the postprocess method to perform SmartyPants replacements once the rendering is complete

# Mixin
class HTMLWithPants < Redcarpet::Render::HTML
  include Redcarpet::Render::SmartyPants
end

# Standalone
Redcarpet::Render::SmartyPants.render("<p>Oh SmartyPants, you're so crazy...</p>")

SmartyPants works on top of already-rendered HTML, and will ignore replacements inside the content of HTML tags and inside specific HTML blocks such as <code> or <pre>.

What? You really want to mix Markdown renderers?

What a terrible idea! Markdown is already ill-specified enough; if you create software that is renderer-independent, the results will be completely unreliable!

Each renderer has its own API and its own set of extensions: you should choose one (it doesn't have to be Redcarpet, though that would be great!), write your software accordingly, and force your users to install it. That's the only way to have reliable and predictable Markdown output on your program.

Still, if major forces (let's say, tornadoes or other natural disasters) force you to keep a Markdown-compatibility layer, Redcarpet also supports this:

require 'redcarpet/compat'

Requiring the compatibility library will declare a Markdown class with the classical RedCloth API, e.g.

Markdown.new('this is my text').to_html

This class renders 100% standards compliant Markdown with 0 extensions. Nada. Don't even try to enable extensions with a compatibility layer, because that's a maintance nightmare and won't work.

On a related topic: if your Markdown gem has a lib/markdown.rb file that monkeypatches the Markdown class, you're a terrible human being. Just saying.

Testing

Tests run a lot faster without bundle exec :)

Boring legal stuff

Copyright (c) 2011, Vicent Martí

Permission to use, copy, modify, and/or distribute this software for any purpose with or without fee is hereby granted, provided that the above copyright notice and this permission notice appear in all copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.