by Adam Brett

Mark Old Posts as Deprecated in Jekyll

This article was published on Tuesday, February 12, 2013 which was more than 18 months ago , this means the content may be out of date or no longer relevant. You should verify that the technical information in this article is still current before relying upon it for your own purposes.

This blog is built with jekyll1, which is a static blogging platform from the guys at github, and is also the engine behind github pages2, where this blog is hosted.

I have written a simple plugin to add a LiquidTag3 to render a warning for all posts that reach a certain age. This is particularly useful for technical blogs such as this one, where the things I'm writing about can move on pretty quickly. The way something was done a year ago isn't necessarily the way I recommend doing it today.

Using the Plugin

If you have a Gemfile, add the chronic gem and run bundle install. If you don’t have a Gemfile, install the gem with gem install chronic --no-ri --no-rdoc.

Now you can add the mark_old_post_tag.rb file to your _plugins folder.

# Mark Old Posts Liquid Tag
# A liquid tag for Jekyll sites to mark old posts as deprecated
# Usage:
#     {% mark_old_posts <time_ago_in_words|date> %}
# Example:
#     {% mark_old_posts 6 months ago %}
#     {% mark_old_posts 1 year ago %}
#     {% mark_old_posts 01/01/2012 %}
# Requires:
#     chronic gem: sudo gem install chronic --no-ri --no-rdoc
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
# @author Adam Brett <[email protected]>
# @license BSD-3-Clause
# @version 0.1
# @link
# @link

require 'chronic'

module Jekyll
  class MarkOldPostTag < Liquid::Tag
    def initialize(tag_name, cut_off, tokens)
      @cut_off_date = Chronic.parse(cut_off)
      @cut_off = cut_off

    def render(context)
      post_date = context.environments.first["page"]["date"]

      unless (post_date.is_a? Time) && (@cut_off_date.is_a? Time)
        return ""

      if context.environments.first["page"]["mark_old_post"] == false
        return ""

      if post_date > @cut_off_date
        return ""

      html_output_for context.environments.first["page"]["date"]

    def html_output_for(post_date)
      post_date = post_date.strftime("%A, %B %d, %Y")
      return <<-HTML
<div class="alert alert-warning">
  <h4>Out Of Date Warning</h4>

    This article was published on <strong>#{post_date}</strong> which was
    <strong>more than #{@cut_off}</strong>, this means the content may be
    out of date or no longer relevant.  You should <strong>verify that the
    technical information in this article is still current</strong> before
    relying upon it for your own purposes.

Liquid::Template.register_tag('mark_old_posts', Jekyll::MarkOldPostTag)

It's not very customisable at the moment. At some point in the future I'd like to allow you to specify the HTML markup without having to modify the plugin itself, but for now you have to modify the output of the html_output_for method if you want to change anything.

To render the warning message, add the tag: {% mark_old_posts <time ago in words|date >%} wherever you want the HTML to be output. You can specify any sort of date string that chronic will understand here, such as 6 months ago, 12 months ago, or an actual date such as 01/01/2012. You can see the example for this site on github4

Excluding Posts/Pages

If you don't want to deprecate an old post, set mark_old_post: false in the YFM for the post or page and the plugin won't render anything.

For exclusive content, including screen-casts, videos, and early beta access to my projects, subscribe to my email list below.

I love discussion, but not blog comments. If you want to comment on what's written above, head over to twitter.