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From: Clint Hepner <clint.hepner@gmail.com>
Newsgroups: gnu.bash.bug
Subject: Re: Tilde expansion in assignment-like context
Date: Mon, 6 Aug 2018 16:04:32 -0400
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Approved: bug-bash@gnu.org
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References: <349F67EA-6EA7-4C8E-8E3A-AC36A82EBFBD@gmail.com> <3f04a0db-0583-d5d9-1faf-75deb76c1219@case.edu>
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> On 2018 Aug 6 , at 3:45 p, Chet Ramey <chet.ramey@case.edu> wrote:
>=20
> On 8/6/18 3:09 PM, Clint Hepner wrote:
>=20
>> Bash Version: 4.4
>> Patch Level: 19
>> Release Status: release
>>=20
>> Description:
>>        A non-initial unquoted tilde is expanded outside of an =
assignment. This
>>        was raised as a question on Stack Overflow, =
https://stackoverflow.com/q/51713759/1126841.
>>=20
>> Repeat-By:
>>=20
>>        $ set +k
>>        $ echo home_dir=3D~
>>        home_dir=3D/Users/chepner
>=20
> Yes. Bash has done this since its earliest days. A word that looks =
like an
> assignment statement has tilde expansion performed after unquoted =3D~ =
and :~
> no matter where it appears on the command line. This makes things like
>=20
> 	make DESTDIR=3D~stager/bash-install
> or
> 	export PATH=3D/usr/local/bin:~/bin:/usr/bin
>=20
> easy and convenient.

Oh, right. For some reason, I had it in my head that this was only =
intended
for builtins like export, and that their status as builtins somehow made
the argument be treated as an assignment. I hadn't thought at all about =
non-builtin
commands like make.

>=20
> The first version I can find that implemented the =3D~ and :~ tilde =
expansion
> prefixes is bash-1.10 (1991). Those early versions would have expanded
> something like `--home_dir=3D~'. The first version that restricted it =
to
> words that satisfied the assignment statement restrictions is bash-2.0
> (1996).
>=20
> Bash doesn't do this when it's in posix mode. The first version that
> implemented that was bash-1.14.0.
>=20
> --=20
> ``The lyf so short, the craft so long to lerne.'' - Chaucer
> 		 ``Ars longa, vita brevis'' - Hippocrates
> Chet Ramey, UTech, CWRU    chet@case.edu    =
http://tiswww.cwru.edu/~chet/