> I was surprised that "Awk '!a[$0]++'" works too (on Mac at least). If I "ls Awk" in \usr\bin, it says Awk is there. If I "ls awk" it says awk is also there—but it seems they're the same file, and it's only pretending Awk is a file. AWK also... I never noticed that before!

I presume this is a side-effect of the macOS default filesystem being case-insensitive. I'm running macOS with a case-sensitive fs and that does not work:

    $ awk
    usage: awk [-F fs] [-v var=value] [-f progfile | 'prog'] [file ...]

    $ Awk
    -bash: Awk: command not found

This default is a topic of great debate.