From: "Lawrence Velázquez" <larryv@zsh.org>
To: "Daniil Iaitskov" <daniil.iaitskov@soostone.com>
Cc: zsh-workers@zsh.org
Subject: Re: bug: nested for loop body is executed once!
Date: Thu, 12 Aug 2021 23:50:34 -0400 [thread overview]
Message-ID: <34dbacca-01ee-4dda-a179-505c57760309@www.fastmail.com> (raw)
In-Reply-To: <CAAyLbqKCubQKvXMa5SRkQYgUYBLThzKujm43PmCAuJg45Psdqg@mail.gmail.com>
On Thu, Aug 12, 2021, at 11:13 PM, Daniil Iaitskov wrote:
> I just spot a following bug on Big Sur zsh 5.8 (x86_64-apple-darwin20.0)
It's not a bug.
> > $ K="1 2 3"
> > $ for i in $(for j in $K; do echo "ddd/$j" ; done) ; do echo "$i" ; done
> > ddd/1
> > 2
> > 3
>
> I would expect following output
> > ddd/1
> > ddd/2
> > ddd/3
By default, zsh does not word-split unquoted parameter expansions;
this behavior differs from most Bourne-adjacent shells. Observe
that your "inner" loop actually only loops once, with $j taking on
the entire value of $K:
% K="1 2 3"
% for j in $K; do echo "<ddd/$j>"; done
<ddd/1 2 3>
However, zsh *does* word-split unquoted command substitutions, so
the output of $(for j in $K; do echo "ddd/$j" ; done) is split into
'ddd/1', '2', and '3', and $i takes on each value in turn.
> > $ for i in $(for j in $(echo 1 2 3); do echo "ddd/$j" ; done) ; do echo "$i" ; done
>
> produce expected output:
> > ddd/1
> > ddd/2
> > ddd/3
In this example, $(echo 1 2 3) is word-split because it is a command
substitution. Thus, $j takes on the values '1', '2', and '3', as
you expected.
> I don't know if this is a feature due to some legacy optimizations.
> I mostly use BASH and this behavior differs from BASH.
> BASH behaves exactly as I expect.
Actually, many zsh users consider the word-splitting of unquoted
parameter expansions to be a misfeature, which zsh's default behavior
remedies. In any case, it's very much intentional. You can obtain
word-splitting behavior with the ${=foo} form:
% K="1 2 3"
% for j in ${=K}; do echo "<ddd/$j>"; done
<ddd/1>
<ddd/2>
<ddd/3>
You can also set SH_WORD_SPLIT, or rewrite the code to use an array.
If you're running code that relies on word-splitting (a POSIX script,
perhaps), you can run it under sh emulation.
> Wow! Are you still using just a mailing list for bug tracking?!
Yes.
--
vq
next prev parent reply other threads:[~2021-08-13 3:51 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-13 3:13 Daniil Iaitskov
2021-08-13 3:47 ` Matthew Martin
2021-08-13 3:50 ` Lawrence Velázquez [this message]
2021-08-14 15:07 ` Daniel Shahaf
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