On Fri, Nov 19, 2021 at 08:02:19AM +0100, Harald Dunkel wrote:
> On 2021-11-18 17:52:29, Robert Elz wrote:
> > Date: Thu, 18 Nov 2021 10:34:40 +0100
> > From: Harald Dunkel <harald.dun...@aixigo.com>
> > Message-ID: <fff15881-9ee7-ce68-6d86-daa81a7d6...@aixigo.com>
> >
> > | at least due to unbalanced parenthesis?
> >
> > Greg's reply was correct, but he didn't explicitly address that point.
> > In sh, characters like { } [ ] (but not ( and )) are just characters.
> > In some scenarios they're required to be paired for things to work, but
> > you can always simply use one (unquoted) anywhere there's a need. They
> > don't have to balance in any way.
> >
>
> "Some scenarios" is the point here. The parenthesis have to balance as
> soon as it comes to shell parameter expansion, which is (or should have
> been) the case here. Something like
>
> : ${SSLDIR:="${JM_WORK}/ssl"
>
> doesn't work, either.
>
> You have to admit that this was a mean pitfall.
You're expecting curly braces to have special meaning. They don't.
Curly braces only have special meaning in three highly specific scenarios:
1) The { appears after a $ character.
2) An unquoted { } pair appears with an unquoted comma between them,
triggering brace expansion.
3) { appears alone in the command position, indicating the start of a
braced command group.
In all other scenarios, { and } are simply ordinary characters with no
special meaning.
Number 2 is tricky. You can get unexpected results if you feed an
ambiguous set of unbalanced curlies to the parser. I would not recommend
using brace expansion in scripts. It's really intended only for
interactive use, to save typing in relatively simple commands.
