When running cat this way, you are in “cooked mode”. A ctrl-d does nothing on a non-empty line.

The shell usually runs in non-cokked, or raw, mode as well as nonblocking mode. Where it sees (nearly) every key you press as you press them. Which is why it " sees" the ctrl-d even when you are not on an empty line.

You can learn more here:

• https://jvns.ca/blog/2024/11/26/terminal-rules/#rule-3-repls-should-quit-when-you-press-ctrl-d-on-an-empty-line. (And more generally, from her various blog posts on the matter)
• https://www.gnu.org/software/mit-scheme/documentation/stable/mit-scheme-ref/Terminal-Mode.html

Here is the author’s blog post: https://www.byran.ee/posts/creation/

Very interesting stuff. I’m waiting for the deep dive on the various issues with great interest.

I get you. I have many similar stories. Where things should have been simple, a 4 steps process. And yet.

Last time was the printer no longer working from my mom’s iPhone. It’s supposed to detect the printer automatically when on the same network, it no longer did. And the stored/“remembered” entry did not work either.

After many troubleshoting steps, I gave up, sent the document to another computer and printed from there. So, clearly, the printer worked (for once) and accepted commands from the LAN.