Truncating Markdown with Redcarpet

gistfile1.rb

require "redcarpet"
require "redcarpet/render_strip"

# I'm not suggesting this is particularly sane, but it works.
# 
# The little bit of regex fixes cases where two paragraphs get squished
# together and you end up with the unsightly
#
#   "end of sentence.New sentence"
#
# when you want
#
#   "end of sentence. New sentence"
#
# (I'm sure there are *loads* of edge-cases it will break on, but
# this sort of handles some common cases, including various bits of
# punctuation.)

def get_content
    # return some text in Markdown here
end

def get_truncated_content(len = 40, ellipsis = "...")
    markdown  = Redcarpet::Markdown.new(Redcarpet::Render::StripDown)
    content   = markdown.render(get_content).split " "
    truncated = content[0...len]

    truncated.join(" ").gsub(/([a-z])(\.|[\.\?\!]?[\'|\"]|\!|\?)([A-Z])/) {
        "#{$1}#{$2} #{$3}"
    } << ( content.size > len ? ellipsis : "" )
end

There's one more elegant solution described here:
http://devblog.boonecommunitynetwork.com/rails-and-markdown/

<%= truncate( strip_tags( markdown(post.description) ), length: 50) %>