Including Boilerplate Files in Jekyll

I use Ark to format my books¹ but Jekyll (the default for GitHub Pages) for my other sites². Each of those sites has a license, a contributor guide, and a code of conduct in its root directory. I don’t want to put YAML headers in them because GitHub renders all of their content when they’re viewed online, but I also don’t want to duplicate the content in other files for rendering on GitHub Pages. My solution is to create a parallel file called (for example) license_.md (with a trailing underscore) that contains this:

---
title: License
permalink: /license/
---

{% include boilerplate.md filename='LICENSE.md' %}

and then put this in _includes/boilerplate.md:

{% capture other %}{% include_relative {{include.filename}} %}{% endcapture %}
{{ other | markdownify | split: "</h1>" | last }}

It only works correctly if the file being included has exactly one h1 header, but well-formed pages shouldn’t have more (or none). I hope it’s useful.

This post motivated in part by a reading of Crichton and Krishnamurthi’s recent paper “A Core Calculus for Documents”.