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From: Bart Schaefer <schaefer@brasslantern.com>
Date: Fri, 9 Nov 2018 18:07:43 -0800
Message-ID: <CAH+w=7YuTY2W6R=tOrD+DijiiboQxJ-EDRROxhB05+gwwQEgRg@mail.gmail.com>
Subject: Re: Use glob patterns while reading a file
To: Daniel Shahaf <d.s@daniel.shahaf.name>
Cc: Zsh Users <zsh-users@zsh.org>
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On Fri, Nov 9, 2018 at 5:22 PM Daniel Shahaf <d.s@daniel.shahaf.name> wrote=
:
>
> > > $(< ./(a|b)(N))
> >
> > That's a special syntax, expecting a single file so that it doesn't try
> > to do globbing.
>
> I think this violates the principle of least surprise.  Grammars should b=
e
> composable and shouldn't have special cases.

Although I can't argue with this from a philosophical standpoint, I
find it astonishing to pretend that zsh ignores that philosophy only
in this particular case.

> The forms =C2=ABfoo=C2=BB and
> =C2=ABprint -r -- "$(<foo)"=C2=BB should always be equivalent (assuming '=
foo' outputs
> a trailing newline).

I don't follow that at all.  =C2=ABfoo=C2=BB is a shell word.  =C2=ABprint =
-r --
"$(<foo)"=C2=BB is the contents of a file identified by the word =C2=ABfoo=
=C2=BB.  In
what context are those equivalent?

> Similarly, =C2=AB<foo=C2=BB and =C2=AB<foo $READNULLCMD=C2=BB are usually
> equivalent, but =C2=AB$(<*)=C2=BB and =C2=AB$(<* $READNULLCMD)=C2=BB are =
not.

The distinction here is that $(...) is a substitution, not a subshell.
It's more like a quoting mechanism (i.e. `foo`).  $(<foo) is NOT an
"optimization" of $({<foo}) (which does work exactly the way you think
it would, globbing-wise), and the "<" in that position in the
substitution is not a redirection operator, even though it looks like
one for mnemonic reasons.  $(<...) is an entirely different thing,
just like $((...)) is a different thing, even though =C2=AB$(=C2=BB and =C2=
=AB<=C2=BB do
not have to be composed without whitespace to form a token.

> was this behaviour intentionally implemented this way?

Yes.