On 10/25/21 8:24 PM, Mark March wrote:
> If -u is on and you declare a simple or associative array 'y' and set it
> empty, then ${y@a} will fail with 'unbound variable'.
It really is unset:
"An array variable is considered set if a subscript has been assigned a
value."
> I was able to repro this under 5.1.0(1)-release and 5.1.8. 5.0.17(1)-release
> does not seem to be affected.
Bash-5.1 fixed some bugs in this area.
> The code to reproduce (output lines begin with #>):
>
> echo $BASH_VERSION
> #> 5.1.0(1)-release
> set -u
> declare -a y=()
> echo ${y@a}
> #> bash: y: unbound variable
Yes, because it's unset, but see below.
> declare -p y
> #> declare -a y=()
> echo ${y[@]}
> #>
The `@' and `*' subscripts are exempted from the nounset option to parallel
the behavior of `$@' and `$*' when there are no positional parameters (the
latter is specified by POSIX).
> set +u
> echo ${y@a}
> #> a
>
> As you can see, turning off -u makes ${y@a} work correctly.
If the `nonunset' option is not enabled, there is a special case for the
`a' transform so it will print the attributes of an unset array variable.
That was the result of a long discussion:
https://lists.gnu.org/archive/html/bug-bash/2020-02/msg00050.html
> I wonder if this is a side-effect of the fix that you described in item (n)
> of the most recent change log:
>
> n. Fixed a bug that caused ${foo@a} to treat foo as an unset variable if it
> was an array without a value for subscript 0/"0" but had other set elements
This is not relevant, there are no set elements.
Chet
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU c...@case.edu http://tiswww.cwru.edu/~chet/
