Batching YAML Front Matter Updates

Posted: July 10, 2023 | Categories: Developer Tools, Eleventy

When I migrated this site from Joomla! to Eleventy, I realized about halfway through the process (after migrating 400 or so articles to .md files) that I wanted to include a description property in articles through YAML front matter properties. This description value became the description for the article in site list views and I also use it to set the description meta tag in the page's HTML Head.

For example, here's the front matter for this post:

---
title: Batching YAML Front Matter Updates
description: This article describes a command-line utility I created to do batch add/update to YAML front matter of all of the markdown files in a folder. This is especially helpful when working with static site generators (SSG).
date: 2023-07-10
showCoffee: 
headerImage: 
headerImageAltText: 
categories:
  - Developer Tools
  - Eleventy
---

Here's the description on the home page:

This article on the home page

And here's the description meta tag:

<head>
    <title>John M. Wargo: Batching YAML Front Matter Updates</title>
    <meta charset="utf-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1, user-scalable=no" />
    <meta name="generator" content="@11ty/eleventy v2.0.1" />
    <meta name="author" content="John M. Wargo">    
    <meta name="description" content="This article describes a command-line utility I created to do batch add/update to YAML front matter of all of the markdown files in a folder. This is especially helpful when working with static site generators (SSG)." />
    <meta name="keywords" content="Developer Tools, Eleventy">    
    <link rel="manifest" href="/manifest.json">
    <link rel="stylesheet" href="/assets/css/main.css" />    
</head>

So, now that you know why I wanted to add the description property to all of my site's articles, the question is how to add it to every article.

Now, I knew I'd have to write the description for each article, but that generally means copying the first paragraph from the article and editing it. What I needed was a simple way to add the property to the front matter, then I can go back in and start copying the content in. For other use cases, I could add a property and value at the same time, even overriding existing values in the process.

I decided to build a command-line utility to do it for me. The utility I created is called YAML Add Property and you can find it on npm.

You can use it to:

Add empty properties to YAML front matter
Add properties and values to YAML front matter
Update existing front matter property values.

To execute the utility, open a terminal window or command prompt, navigate to the Eleventy project folder (it doesn't have to be an Eleventy project), and execute the following command:

npx yaml-add-property

The module will prompt you for the operational parameters to use while executing:

Prompt	Input	Description
Source folder	String	The folder name, relative to the execution folder, for the source files.
Property name	String	The property name added to the YAML front matter.
Property value	String	The value assigned to the property added to the front matter. When omitted, defaults to a blank string (`''`)
Override existing	Yes/No	Controls whether the package overrides the property value if the file already has the property in its front matter.
Process subfolders	Yes/No	Controls whether the package recurses through sub folders when building the file list

To display additional information in the console during execution, enable debug mode by adding a -d to the command line.

When the command executes, it will update the console as shown in the following figure:

an image of the command running in the terminal

I hope you find this utility helpful.

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Header image: Photo by Ashim D’Silva on Unsplash.