build-your-own-shell VS raspberry-pi-os

https://github.com/tokenrove/build-your-own-shell

I think you right, and implementing core utils is a nice exercise in system programming.

C: Build Your Own Shell

Last but not the least, learning by doing is fun so you can check out - raspberry-pi-os (writing an os from scratch) - https://github.com/s-matyukevich/raspberry-pi-os

CheesecakeOS for Raspberry Pi Volume 0: Booting, Processes, and Virtual Memory is the first in what I hope is a series of github markdown tutorials or volumes on bare-metal from-scratch operating system development.

I have dreamed of contributing to the Linux Kernel, but have yet to find the courage to jump in and do so. I started by attempting to read Understanding the Linux Kernel by Daniel Bovet and Marco Cesati, but found it was too advanced for me at the time. I found another text I credit with advancing my understanding, Computer Systems: A Programmer's Perspective by Randall Bryant and David O'Hallaron. I worked on the self-study labs from their book website, and found them to be a superb educational tool.

Further, then becoming interested in what creating an operating system actually means, I stumbled upon Sergey Matyukevich's Rasberry-Pi-OS github repo (https://github.com/s-matyukevich/raspberry-pi-os). I wanted to expand on his tutorial, for my own education, and, in the best case, for the benefit of others.

There are many ideas taken from Linux in the implementation, as when I didn't know how to proceed, that is the source I would consult. Though, I attempt to simplify and explain the details in the text. The implementation stops short of implementing or supporting a file system, the subject of the next volume.

Not familiar with this myself but aiming to start soon. Have found a nice youtube series for low level development on the RPi, not sure which version he uses, but reportedly it works for some on RPi 4. He also has a subreddit:

Here's one tutorial: https://github.com/s-matyukevich/raspberry-pi-os

C: Learning operating system development using Linux kernel and Raspberry Pi