gistfile1.rb

require 'kramdown'
require 'uri'
require 'pathname'

body =<<EOS
> [link](test)
>> [google](http://www.google.com)
EOS

kramdown = Kramdown::Document.new(body)
nodes = [kramdown.root]
while(node = nodes.shift)
  nodes += node.children
  case(node.type)
  when :a
    href = node.attr['href']
    if URI.parse(href).scheme.nil? && Pathname.new(href).relative?
      node.attr['href'] = '/pages/' + href
    end
    node.attr['href'] = node.attr['href']
  end
end

p kramdown.to_html