Generating redirects file with Eleventy

As part of my migration, I wanted to make sure all the old urls redirected to the new ones. Netlify lets you add a _redirects file with all your redirect rules.

After gathering all the old URLs, it was pretty straightforward. I made _redirects.njk and made sure it was not using my default layout and excluded it from collections. Loop through all my posts and put the old URL, new URL, and 301 . Done.

---
permalink: /_redirects
layout: false
eleventyExcludeFromCollections: true
---
{%- for post in collections.posts -%}
	{%- if post.data.oldUrl -%}
	{%- set absolutePostUrl = post.url | absoluteUrl(metadata.url) -%}
		{{post.data.oldUrl | removeSite }} {{absolutePostUrl}} {{ '301' }}
		{%- if not loop.last -%}
		  {{ '\n' }}
		{%- endif -%}
	{%- endif -%}
{%- endfor -%}

One gotcha for me was {% vs {%-. Adding the - strips whitespace which is exactly what I wanted.

removeSite is a custom filter that removes https://samwarnick.com from the old URL string. Multiple ways I could've handle this, but this is what I did.