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Re: No word splitting for assignment-like expressions in compound assign

From: Oğuz
Subject: Re: No word splitting for assignment-like expressions in compound assignment
Date: Mon, 27 Jul 2020 11:05:31 +0300

27 Temmuz 2020 Pazartesi tarihinde Alexey Izbyshev <izbyshev@ispras.ru>

> On 2020-07-27 10:06, Lawrence Velázquez wrote:
>> On Jul 27, 2020, at 1:31 AM, Dale R. Worley <worley@alum.mit.edu> wrote:
>>> Interesting.  The documentation for 4.2.53(1) says this about parameter
>>> assignments generally, with no special rules for compound assignments:
>>>       All
>>>       values undergo tilde expansion, parameter and variable expansion,
>>> com-
>>>       mand  substitution, arithmetic expansion, and quote removal (see
>>> EXPAN-
>>>       SION below).  ...  Word  splitting  is  not
>>>       performed,  with the exception of "$@" as explained below under
>>> Special
>>>       Parameters.  Pathname expansion is not  performed.
>>> So it seems like the word splitting in "A=(X$Z)" is incorrect.  So is
>>> pathname expansion in that context.
>> If word splitting were not performed in compound assignments, this...
>>     foo=(a b c)
>> ...would not work. If pathname expansion were not performed in compound
>> assignments, this...
>>     foo=(*)
>> ...would not work. Arrays would become significantly less usable if
>> word splitting and pathname expansion were not allowed in compound
>> assignments.
>> To be clear, I don't consider word splitting and expansions in compound
> assignments to be a problem: this is well-known and long-standing behavior,
> even though it doesn't seem to be explicitly documented. In particular, I
> expect word splitting to happen in "A=(X$Z)" case. But I expect it to
> happen in "A=(X=$Z)" too, and the lack of it seems unintentional to me.

I agree, anything that forms a valid assignment statement in isolation is
exempt from word splitting and that indeed seems like a bug or very poor
implementation choice.

    $ Z='a b'
    $ A=(X=$Z X[123]=$Z X[qwerty]=$Z X+=$Z)
    $ declare -p A
    declare -a A=([0]="X=a b" [1]="X[123]=a b" [2]="X[qwerty]=a b"
[3]="X+=a b")

> Alexey


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