Change Jekyll site baseurl without breaking links to existing posts

Question

I have a Jekyll blog using the Minimal Mistakes theme. It's hosted through GitHub Pages, with a custom domain name. The github repo is called eg me.github.io. Currently, the blog is at something like http://www.example.com, so each post comes up like http://www.example.com/trouble-with-urls/.

I want to change it so that it's all at http://www.example.com/blog instead. I have added baseurl: "/blog" to my _config.yml file and now the posts are at the right place, http://www.example.com/blog/trouble-with-urls/. However, I now have two problems: all my image links are broken, and more importantly the links to individual posts are also broken.

Is it possible to automatically redirect posts? I looked at the jekyll-redirect-from gem, but I don't really understand it. It looks like the baseurl is automatically included in the path for the redirect_from: and I can't work out how to ignore it. The readme for that gem says, for customising, "Simply create a layout in your site's _layouts directory called redirect.html." Is there something I can do with that?

Actually I would also like to change the permalinks as well, to add dates, but I'm trying to focus on one problem at a time! Eventually the final URL of each post should be like http://www.example.com/blog/2021/02/13/trouble-with-urls/.

For the images, they are currently all hardcoded like ![url trouble](/assets/images/2021-02/ugh.png). I can fix the path by adding in "/blog", to make it ![url trouble](/blog/assets/images/2021-02/ugh.png) but I think this might be a bad way to link images anyway. I saw that there are {% %} tags for links but can't find any resources about using them for images. Is it possible?

Answer 1

I managed to get this working, so here's what I did in case anyone else tries similar in future.

Adding a baseurl in _config.yml didn't work. Instead, I duplicated my repo, to take advantage of Github Pages' allowance for 1 User site but many Project sites.

One repo remained as me.github.io. I renamed the copy to blog, and added a gh-pages branch. This made GitHub automatically deploy it at me.github.io/blog.

Within the blog repo, I changed the permalinks to the style I wanted. The images were fine as the relative paths hadn't changed.

Within the original me.github.io repo, I first changed the home page (by editing the Minimal Mistakes html files) to hide all posts. Then I added a link at the top of the page to their new home, at me.github.io/blog. The blog is now successfully a subsidiary of the main site.

So that old links wouldn't break, I kept all the existing post files in the me.github.io repo. I used the jekyll-redirect-from gem to add redirects into each post for the new address. This was done by manually adding a line into the Front Matter of each, saying eg redirect_to: http://www.example.com/blog/2021/02/13/trouble-with-urls/. I also deleted all the post content of these posts, so only the Front Matter was left.

All future posts will be made within the blog repo, and so they will have the correct URLs.