Re: Associative array keys are not reusable in (( command

[Oğuz]

On Fri, Jan 8, 2021 at 2:14 PM Koichi Murase <myoga.murase@gmail.com> wrote:

> This topic actually pops up occasionally.  FYI, you can also see the
> following discussions:
>
> https://lists.gnu.org/archive/html/bug-bash/2014-06/msg00003.html
> https://lists.gnu.org/archive/html/bug-bash/2014-10/msg00154.html
> https://lists.gnu.org/archive/html/bug-bash/2015-02/msg00066.html
>
> 2021年1月8日(金) 18:21 Oğuz <oguzismailuysal@gmail.com>:
> > `(( assoc[\$key]++ ))' works as usual, but this is not documented as
> > far as I know,
>
> This is explained in the first link above by quoting two sentences in
> the document, but I agree with you that this is so non-trivial that
> it's worth explicitly documenting IMHO.
>

You are right, the first quote explains it.


> > Considering that the following two works, it doesn't make much sense
> > that `(( assoc[$key]++ ))' doesn't.
>
> I think the POSIX expansion order should be applied to, for example,
> $((assoc[$key]++)).  In this case, the arithmetic evaluation of the
> whole expression should be performed only after $key in
> $((assoc[$key]++)) is expanded.  There is no reason to introduce a
> different expansion rule of `((...))' from that of `$((...))'.  It
> feels a bit strange to me to expand `$key' in `(( assoc[$key]++ ))'
> after determining the arithmetic structure thinking the normal
> expansion order.
>

But there already is a different expansion rule. While `(( assoc['$key']++
))' works, `: $(( assoc['$key']++ ))' fails with a bad subscript error.


> > It would be better if at least quoting the key by means of parameter
> > transformation or `printf %q' worked, because these are the first
> > workarounds that come to mind;
>
> This is maybe a good idea.  From Bash 5.1, the single quotation is
> not a subject to the quote removal of `(( ... ))', so we can use the
> single quotation as a part of the arithmetic expression.  We can just
> introduce the string literal of the form '...' or $'...' in the
> arithmetic evaluator.
>

$'...' would be nice, it would even fix existing scripts that rely on @Q or
%q.


> --
> Koichi
>