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From: Ilkka Virta <itvirta@iki.fi>
Newsgroups: gnu.bash.bug
Subject: Re: Backslash missing in brace expansion
Date: Fri, 6 Dec 2019 22:29:14 +0200
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Approved: bug-bash@gnu.org
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To: Eric Blake <eblake@redhat.com>, Martin Schulte <gnu@schrader-schulte.de>, bug-bash@gnu.org
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Xref: csiph.com gnu.bash.bug:15704

On 6.12. 21:36, Eric Blake wrote:
> On 12/5/19 10:53 PM, Martin Schulte wrote:
>=20
>>>> (2019-11-11) x86_64 GNU/Linux $ echo ${BASH_VERSINFO[@]}
>>>> 4 4 12 1 release x86_64-pc-linux-gnu
>>>> $ set -x
>>>> $ echo {Z..a}
>>>> + echo Z '[' '' ']' '^' _ '`' a
>>>> Z [=A0 ] ^ _ ` a
>>>>
>>>> It looks as if the backslash (between [ and ] in ASCII code) is
>>>> missing in brace expansion. The same behaviour seems to be found in
>>>> bash 5.0.
>>>
>>> It's an unquoted backslash, which is removed by quote removal when th=
e
>>> words are expanded. Look at the extra space between `[' and `]'; that=
's
>>> the null argument resulting from the unquoted backslash.
>>
>> Yes - sure. But then I'm wondering why the unquoted backtick doesn't
>> start command substitution:
>=20
> It may be version dependent:
>=20
> $ echo ${BASH_VERSINFO[@]}
> 5 0 7 1 release x86_64-redhat-linux-gnu
>=20
> $ echo b{Z..a}d
> bash: bad substitution: no closing "`" in `d

I get that with 4.4 and 'echo b{Z..a}d' too, the trailing letter seems=20
to trigger it.

Which also doesn't seem to make sense, but one might argue that {Z..a}=20
doesn't make much sense in the first place. Seriously, is there an=20
actual use case for such a range?

It doesn't seem to even generalize from that if you go beyond letters,=20
so you can't do stuff like generating all the printable ASCII characters=20
with it in Bash.


--=20
Ilkka Virta / itvirta@iki.fi