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From: =?utf-8?Q?Lawrence_Vel=C3=A1zquez?= <vq@larryv.me>
Newsgroups: gnu.bash.bug
Subject: Re: No word splitting for assignment-like expressions in compound assignment
Date: Mon, 27 Jul 2020 03:06:22 -0400
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Cc: Alexey Izbyshev <izbyshev@ispras.ru>, bug-bash@gnu.org
To: "Dale R. Worley" <worley@alum.mit.edu>
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Xref: csiph.com gnu.bash.bug:16620

> On Jul 27, 2020, at 1:31 AM, Dale R. Worley <worley@alum.mit.edu> =
wrote:
>=20
> Alexey Izbyshev <izbyshev@ispras.ru> writes:
>> I have a question about the following behavior:
>>=20
>> $ Z=3D'a b'
>> $ A=3D(X=3D$Z)
>> $ declare -p A
>> declare -a A=3D([0]=3D"X=3Da b")
>> $ A=3D(X$Z)
>> $ declare -p A
>> declare -a A=3D([0]=3D"Xa" [1]=3D"b")
>>=20
>> I find it surprising that no word splitting is performed in the first=20=

>> compound assignment.
>=20
>> * Brace expansion is performed for "A=3D(X=3Da{x,y}b)" by all bash =
versions=20
>> mentioned above (which is inconsistent with normal variable =
assignment).
>> * Globbing for "A=3D(X=3Da?b)" is performed by bash 3.1.17, but not =
by other=20
>> versions.
>=20
> Interesting.  The documentation for 4.2.53(1) says this about =
parameter
> assignments generally, with no special rules for compound assignments:
>=20
>       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 "$@" as explained below under =
Special
>       Parameters.  Pathname expansion is not  performed.
>=20
> So it seems like the word splitting in "A=3D(X$Z)" is incorrect.  So =
is
> pathname expansion in that context.


If word splitting were not performed in compound assignments, this...

    foo=3D(a b c)

...would not work. If pathname expansion were not performed in compound
assignments, this...

    foo=3D(*)

...would not work. Arrays would become significantly less usable if
word splitting and pathname expansion were not allowed in compound
assignments.

vq=