Emacs

Eglot + various system lsps

Shell-scripting

Isn't shell-script-mode available in vanilla installation? For me it automatically gets enabled when I open .sh file

Markdown

https://www.emacswiki.org/emacs/MarkdownMode

HTML+CSS

Haven't written these in a while, but I expect there will be modes for them

Rust

https://github.com/rust-lang/rust-mode?tab=readme-ov-file#melpa

And in general:
https://www.emacswiki.org/emacs/InstallingPackages
and
https://www.gnu.org/software/emacs/manual/html_node/emacs/Customization-Groups.html

I use org mode for everything. org-babel let's you embed code and execute it in the document or tangle code blocks into external scripts.

Spacemacs

Hello! Welcome to Emacs!

Contrary to the other commenters, I would suggest starting with an out-of-the-box Emacs and only adding the things you need, as you need them.

As for your question, could you provide more detail about your expectations?

In the absence of it, I'll give you some generic responses:

• Shell-scripting: Emacs should support this out of the box
• Markdown: There is a popular package that provides a major mode markdown-mode: https://github.com/jrblevin/markdown-mode
• HTML+CSS: There is a major mode html-mode that is included by out of the box: https://www.gnu.org/software/emacs/manual/html_node/emacs/HTML-Mode.html
• For language support, the response will depend on your needs/expectations. If all you want is highlighting, it will probably work out of the box. For advanced features, you'll need to look at Eglot or something like lsp-mode

I used to maintain my own Emacs config, but I switched to Doom years ago and never looked back. I appreciate the community aspect that lets it be better integrated and tested than I had time to manage on my own.

I use it as my primary environment for everything you mentioned and its excellent. The initial setup is fairly easy too.

And because it's Emacs, if there's something you don't like, you can change it! 😄

Base Emacs 29 will do a lot for you in those areas, especially with rust-ts-mode (Treesitter powered Rust mode), Markdown mode, Company (a completion tool), and Eglot (lsp server client). I also recommend adding Which-Key to help figure out the bindings in different modes. Built-in eshell is great for scripting / terminal needs.

For a kickstarter config, System Crafters' is pretty nice and will mostly keep you to built ins with good documentation of why they chose things. https://github.com/SystemCrafters/crafted-emacs/ and they have a Rust example config using their modules in their examples.

Doom Emacs and Space Emacs are cool too to show some possibilities and get a full featured ide earlier, but there those setups due add their own learning steps.

I second looking at System Crafters' resources. One thing that helped me was their emacs from scratch video series.

And as a heavy Markdown user, I initially built my config around Markdown. But several years later I've found I now use org-mode almost exclusively instead. They both fill the same niche in my workflow, but org-mode can do a lot more.

If you're new(ish) to Emacs, I would strongly suggest using a kit like Doom Emacs. It sets up some modern defaults, and makes it far, far simpler to set up a good environment for whatever languages you want. And the wonderful thing is that you can keep using Doom!