Jekyll treats front matter like any other piece of data. You can add [pretty much] anything you want there, and it will be available for you to use programmatically.
Access within a post/page:
Let’s say you are writing a post about Avatar and want to reference the film: front matter in the content of your post. You can use this example to display it within the post:
/_posts/2022-06-20-all-about-avatar.md
---
title: All about Avatar
date: 2022-06-20
film: Avatar (2009)
---
## {{page.title}}
This is my review of {{page.film}}.
The result would look something like this:
Even though that is technically a post, you do not use use post.film, because, at this point, you are displaying front matter on a page, which is why you should use page.film.
Add to a list of posts
Let’s say you want a summary page that lists all the posts you made about films. Here is a basic method to do that:
/index.md
---
layout: default
title: "All my posts about films!"
---
## {{page.title}}
<p></p>
{%- for post in site.posts -%}
Title: <a href="{{post.url |relative_url}}">{{post.title}} / {{post.film}}</a><br>
{%- endfor -%}
The result will be a list of all posts on your site, like this:
Notice in the screenshot that there is a post without the title Introducing my new blog. That post does not have the film YAML front matter, which may be fine for you. However, it is not a list of films, so you will need to modify your code a bit with assign, using a where_exp, like this:
/index.md
---
layout: default
title: "All my posts about films!"
---
## {{page.title}}
<p></p>
{%- assign posts = site.posts | where_exp: 'post', 'post.film' -%}
{%- for post in posts -%}
Title: <a href="{{post.url |relative_url}}">{{post.title}} / {{post.film}}</a><br>
{%- endfor -%}
Now, the output will look like this:
You might be wondering how that where_exp works. It says, “look in site.posts and only give me the results if there is a film: front matter item”.
Another thought: Jekyll Collections
If you find you will be writing about films, tv shows, books, or other topics, you might want to make your life a little easier and use Jekyll Collections.
With Collections, you can create the equivalent of a _posts folder for your films, like /_films and tv shows, like /_tv and so on.
Here is the official documentation for Jekyll Collections:
Here is a post on how to use collections in a similar fashion you may (or may not) want to use: