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Jekyll Plugin to Load Asciinema Recordings Locally

Posted on 24 Sep 2023, tagged JekyllBlogcommand lineAsciicast

Asciinema is a wonderful tool to record Linux terminal. It saves the records as a text format called Asciicast. However, it has a strong integration with its website. Especially if you want to embed the recordings into the web page use some simple JS code like this:

<script src="https://asciinema.org/a/14.js" id="asciicast-14" async></script>

You need to share the recordings to Asciinema’s website and need to link an account with the recordings, otherwise they will be deleted after 7 days, which I just found out yesterday. I don’t want my blog to rely on some third party website for core content, so I need a way to load the recordings from my website itself.

Lucky, the Asciinema Javascript player is open source and support to load recordings from a url out of box. First you need to import the CSS:

<link rel="stylesheet" type="text/css" href="/asciinema-player.css" />

This is no big deal since this can be put in Jekyll’s template. Then you need some JS code like this:

<div id="demo"></div>
 ...
<script src="/asciinema-player.min.js"></script>
<script>
  AsciinemaPlayer.create('/demo.cast', document.getElementById('demo'));
</script>

It’s a little bit too much for embedding a terminal recording in a blog. However, with the powerful Jekyll plugin system, We can write a plugin to make it simpler so that we can just use a tag to include it:


{% asciicast <id> %}

Here is the implementation, it’s also in my blog’s Github repo:

module Jekyll
  class RenderAsciicastTag < Liquid::Tag

    def initialize(tag_name, text, tokens)
      super
      @text = text.strip
    end

    def render(context)
      "<div id=\"cast-#{@text}\"></div>" \
      '<script src="/static/js/asciinema-player.min.js"></script>' \
      "<script>AsciinemaPlayer.create('/static/asciicasts/#{@text}.cast', document.getElementById('cast-#{@text}'), {rows: 10, autoPlay: true});</script>"
    end
  end
end

Liquid::Template.register_tag('asciicast', Jekyll::RenderAsciicastTag)

It will find the recordings under /static/asciicasts/{id}.cast and load from there.

Put this file under _plugins and happy hacking!