gistfile1.txt

        AUTO_LINK_RE = %r{
            ( https?:// | www\. )
            [^\s<]+
          }x unless const_defined?(:AUTO_LINK_RE)

        BRACKETS = { ']' => '[', ')' => '(', '}' => '{' }

        # Turns all urls into clickable links.  If a block is given, each url
        # is yielded and the result is used as the link text.
        def auto_link_urls(text, html_options = {})
          link_attributes = html_options.stringify_keys
          text.gsub(AUTO_LINK_RE) do
            href = $&
            punctuation = ''
            left, right = $`, $'
            # detect already linked URLs and URLs in the middle of a tag
            if left =~ /<[^>]+$/ && right =~ /^[^>]*>/
              # do not change string; URL is alreay linked
              href
            else
              # don't include trailing punctuation character as part of the URL
              if href.sub!(/[^\w\/-]$/, '') and punctuation = $& and opening = BRACKETS[punctuation]
                if href.scan(opening).size > href.scan(punctuation).size
                  href << punctuation
                  punctuation = ''
                end
              end

              link_text = block_given?? yield(href) : href
              href = 'http://' + href unless href.index('http') == 0

              content_tag(:a, h(link_text), link_attributes.merge('href' => href)) + punctuation
            end
          end
        end