Example Marked custom processor for previewing Jekyll posts

jekyllpre.rb

#!/usr/bin/ruby
# For use with Marked <http://markedapp.com> and Jekyll _posts
#   turns
# {% img alignright /images/heythere.jpg 100 100 "Hey there" "hi" %}
#   into
# <img src="../images/heythere.jpg" alt="Hey there" class="alignright" title="hi" />
#
# replaces alignleft and alignright classes with appropriate style attribute
#
# Processes final output with /usr/bin/kramdown (install kramdown as system gem: `sudo gem install kramdown`)

content = STDIN.read

def e_sh(str)
  str.to_s.gsub(/(?=[^a-zA-Z0-9_.\/\-\x7F-\xFF\n])/, '\\').gsub(/\n/, "'\n'").sub(/^$/, "''")
end

content.gsub!(/\{% img (.*?) %\}/) {|img|
  if img =~ /\{% img (\S.*\s+)?(https?:\/\/\S+|\/\S+|\S+\/\s+)(\s+\d+\s+\d+)?(\s+.+)? %\}/i
    classes = $1.strip
    src = $2
    size = $3
    title = $4

    if /(?:"|')([^"']+)?(?:"|')\s+(?:"|')([^"']+)?(?:"|')/ =~ title
      title  = $1
      alt    = $2
    else
      alt    = title.gsub!(/"/, '&#34;') if title
    end
    classes.gsub!(/"/, '') if classes
  end

  style = %Q{ style="float:right;margin:0 0 10px 10px"} if classes =~ /alignright/
  style = %Q{ style="float:left;margin:0 10px 10px 0"} if classes =~ /alignleft/

  %Q{<img src="..#{src}" alt="#{alt}" class="#{classes}" title="#{title}"#{style}>}
  # "![#{alt}](..#{src} \"#{title}\")"
}
puts %x{echo #{e_sh content}|/usr/bin/kramdown}