Re: Nofork ${{var}...} edge cases

[Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>]

On Sat, May 31, 2025 at 12:21 AM Mikael Magnusson <mikachu@xxxxxxxxx> wrote:
>
> This just came up on IRC, and I'm not sure what the currently expected
> result is here, and I couldn't find any test coverage for this either:
> % REPLY=before; echo $REPLY ${ echo 1} ${| REPLY=2} $REPLY
> before 1 2 1
>
> I find it very surprising that REPLY is overwritten by ${ echo 1}

Not really obvious but you have to have a space between "1" and "}" --
spaces inside BOTH braces, not just the left one.  Without the final
space, this is being interpreted as
  ${{} echo 1}
which defaults to using $REPLY in the scope of the caller, just as if you wrote
  ${{REPLY} echo 1}.
REPLY is chosen there because ${| echo 1} uses REPLY.

${{} ...} is permitted because ${} is permitted.  Overlooked when
writing the doc, sorry.

${ ... } (with the spaces on both ends) actually uses an undocumented
read-only local ${.zsh.cmdsubst}.

It might be possible to make it a bad substitution to skip the final space.