`ls` seems to have changed (unless ls has distro specific arguments). When I use `ls -r` I get reverse order. To get sub-directories, I have to use `ls -R`. I'm running Mint.

I don't think it has changed. IIRC recursive in ls has always (in the near ¼ century I've been using Linux and occasionally other unix-a-likes) been specified with an upper-case R. I suspect an uncorrected typo.

These might help:

* https://github.com/jlevy/the-art-of-command-line notes and tips on using the command-line, suitable for both beginners and experienced users

* https://github.com/tldr-pages/tldr collection of community-maintained help pages for command-line tools

* http://www.compciv.org/unix-tools/ examples for most common usecases

* https://devmanual.gentoo.org/tools-reference/bash/index.html Bash reference cheatsheet

Thank you!