finding locations of many files via kpse

[Karl Berry]

Hi Erik,

    in GNU's getopt library, long options are always preceded
    by two dashes. 

Well, that is the default, but it is quite common to call
getopt_long_only, not getopt_long, and then -mark is the same as --mark.
(And --mar is also accepted, etc.)

Specifically, I used getopt_long_only pervasively throughout the TeX
engines, drivers, etc., back when I unified option handling among the
programs extant in the late 1980s. Programs added since then sometimes
use getopt_long_only, sometimes not. We use the Perl equivalent of
getopt_long_only in tlmgr and install-tl.

    My hope is that lua-alt-getopt is somewhat aligned with other CLIs
    within TeX Live, but I'm guessing this script is for internal use.

I don't know what you mean. lua-alt-getopt was an early Lua option
parsing package written independently by Aleksey Cheusov (and not
updated since 2010). It's not used within TL as far as I know.
Grepping in a bindir, I see that luaotfload-tool uses it, and, so far as
that grep showed, nothing else.

    I'll have to admit that I'm a great fan of GNU's getopt semantics. 

Me too. That's why I used it. At some point I had to copy the source
files into TL (kpathsea/getopt*) because of incompatibilities, but it's
still GNU getopt.

    However, from a historical standpoint, the alternative getopt
    library within TeX Live should be favored instead,

I'm not aware of any "alternative library" in TL (for C).

Happy option hacking,
Karl