Re: feature todo .. be able to unset vars at assignment stage , without unset util , for coding language fair extendment

[alex xmb sw ratchev]

On Fri, Feb 23, 2024, 13:26 Zachary Santer <zsanter@gmail.com> wrote:

> On Thu, Feb 22, 2024 at 10:58 PM Greg Wooledge <greg@wooledge.org> wrote:
>
> > On Thu, Feb 22, 2024 at 10:52:59PM -0500, Zachary Santer wrote:
> > >
> > > Maybe something like var=${<>} could unset var. Something between the
> > curly
> > > braces that would just be a syntax error otherwise.
> >
> > ${} is nicely erroneous, currently, as is ${~}.
> >
>
> This would look inconsistent with how the rest of variable assignments work
> when you're trying to unset an entire array, though.
>
> var='whatever' sets var[0] if var is already an indexed or
> associative array, so expecting var=${<>} or var=${~} to unset the entire
> array doesn't work. var[@]='whatever' will set the literal index '@' in an
> associative array, so var[@]=${~} is out. Same applies for *.
>
> The parser can tell ${var[@]} and ${var['@']} apart, though. That would
> leave you with syntax that doesn't look like an assignment at all.
> ${~var[@]} to unset the entire array. ${~var['@']} to unset the element
> with index '@'.
>
> Given the use case of unsetting a variable in a command's environment,
> you're still going to end up with something that doesn't look consistent:
> PATH='/usr/bin' ${~BASH_ENV} ./script
> to set PATH like this and unset BASH_ENV in ./script's environment.
>
> Given that, I might expect
> ${~var}
> to unset var on its own without having to follow :.
>
> Honestly, it's probably better off without the dollar sign even, since it's
> not going to look like an assignment, and it isn't an expansion. But {~var}
> isn't a syntax error, it's just a regular word, so who knows if somebody
> already has it in a script for some reason?
>
> I imagine this feature would now require more changes to the parser, too.
> Is it worth it? Anybody got better ideas?
>

its gotta work in more complex just unset itself after
eg in parameter expansion
actually ${~var} to use and unset is quite nice
im not sure about more advanced syntax , as in parameter expansion

greets

>