2016-02-03 23:43:37 +0000, Martijn Dekker:
> bash treats an empty array as if it were an unset variable, which seems
> very illogical as empty is quite distinct from unset:
>
> $ myarray=()
> $ [[ -v myarray ]] && echo set || echo unset
> unset
[[ -v var ]] is for scalar variables (AFAICT).
bash like ksh arrays to some extend overload. (as in $var is ${var[0]}).
$ bash -c 'a[1]=x; [[ -v a ]]' || echo unset
unset
$ bash -c 'a[1]=x; [[ -v a[@] ]]' && echo set
set
~$ bash -c 'a=(""); [[ -v a[@] ]]' && echo set
set
In:
$ bash -c 'a=(); [[ -v a[@] ]]' || echo unset
unset
It still returns "unset" as none of the elements are set.
You can always check whether the variable is "bound" with
declare -p
declare -p array >/dev/null 2>&1 && echo set
I don't know how one can check whether the variable is
/declared/ or not though (when it's not "bound").
> $ set | grep ^myarray= # yet, it's set:
> myarray=()
> $ set -u
> $ for i in "${x[@]}"; do :; done
> bash: x[@]: unbound variable
>
> Note also that the "unbound variable" error is inconsistent with the
> behaviour of "$@"; I would have thought that, logically, "$@" and
> "${x[@]}" should behave the same way, since arrays are implemented as a
> logical extension of the positional parameters concept.
Agreed.
> zsh and ksh93 can distinguish between empty and unset arrays.
[...]
In zsh, arrays are a clearly distinct type.
You may want to check the archieve, I beleive it's been
discussed before.
--
Stephane
