Re: Backslash missing in brace expansion

[Ilkka Virta]

On 6.12. 21:36, Eric Blake wrote:
> On 12/5/19 10:53 PM, Martin Schulte wrote:
>
> > > > (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 [  ] ^ _ ` 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 the
> > > 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:
>
> It may be version dependent:
>
> $ echo ${BASH_VERSINFO[@]}
> 5 0 7 1 release x86_64-redhat-linux-gnu
>
> $ 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 
to trigger it.

Which also doesn't seem to make sense, but one might argue that {Z..a} 
doesn't make much sense in the first place. Seriously, is there an 
actual use case for such a range?

It doesn't seem to even generalize from that if you go beyond letters, 
so you can't do stuff like generating all the printable ASCII characters 
with it in Bash.


--
Ilkka Virta / itvirta@iki.fi