I really like this feature of rsync (trailing "/" means copy the directory contents to the dest, no trailing "/" means copy the directory itself). Other tools, like cp, don't have any way at all to say copy the directory contents to the dest, and for those tools the result depends on whether or not the destination already exists and is a directory (you might end up with a duplicate nested directory). Rsync produces the same result whether the destination already exists or not.

rsync, or at least the version I had would behave differently for 'rsync a b' vs 'rsync a/ b/', even though I added the slash for both sides.

And `cp`.

Yes, into versus onto. Luckily we have AI to write our command lines.