Re: Local variable can not unset within shell functions

[Chet Ramey]

On 7/11/24 9:42 AM, Dr. Werner Fink wrote:
> Hi,
>
> I've a report that with later bash the following which works in bash-4.2
>
>   x () {
>    local x=y
>    declare -p x
>    echo $x
>    unset x
>    declare -p x
>    echo $x
>   }
>
> with
>
>   linux-40cm:~ # x () {
>   >   local x=y
>   >   declare -p x
>   >   echo $x
>   >   unset x
>   >   declare -p x
>   >   echo $x
>   >  }
>   linux-40cm:~ # x
>   declare -- x="y"
>   y
>   -bash: declare: x: not found
>   
> but with bash-5.X the reporter sees (and complains)
>
>   sl15sp5:~ # x () {
>   >   local x=y
>   >   declare -p x
>   >   echo $x
>   >   unset x
>   >   declare -p x
>   >   echo $x
>   >  }
>   sl15sp5:~ # x
>   declare -- x="y"
>   y
>   declare -- x

The variable is unset: it has attributes (local) but has not been assigned
a value.

The idea behind preserving the local attribute is that the variable will
continue to be reported as unset while in the function, but assigning it
a new value will preserve it as a local variable. This is how bash has
behaved since 1995 (bash-2.0).

The bug in bash-4.2 was that it didn't tell you which instance of a
variable the shell would modify if it were subsequently assigned a value.
The local variable still exists, is unset, and would be used by expansions
and assignments, but `declare' would not tell you that.

This would have been clearer to see (and more misleading) if the variable
x also had a value at the global scope.

A discussion that prompted the change starts at

https://lists.gnu.org/archive/html/bug-bash/2013-11/msg00000.html

Chet
--
``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/

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