for context, this came up when trying to do $((foo[bar[i%${#bar[@]}]]))
which has no immediate equivalent without $
On Mon, Jun 30, 2025, 19:45 Robert Elz <k...@munnari.oz.au> wrote:
> Date: Mon, 30 Jun 2025 10:44:24 -0400
> From: Greg Wooledge <g...@wooledge.org>
> Message-ID: <20250630144424.gj32...@wooledge.org>
>
> | Unfortunately, that's not true. You need $ if you want to use any
> | special parameters in an arithmetic context, such as $# or $1.
>
> There are a zillion other reasons why it can be needed as well,
> One is to have a variable operator in the expression (say op=+ or op=-
> and then use ${op} as a binary operator.)
>
> Further I often embed command substitutions within arithmetic, that's
> useful as well (and unless the results would be different using the old
> form cmdsub (`...`) which it doesn't seem to be) this really should be
> fixed (I personally don't care much about the (()) command, but the
> same issue arises in $(( )) -- though that's not surprising, the two
> should be the same for everything except the final result use).
>
> And even more, it should be possible to have the entire expression
> be the result of a variable expansion
> ((${exp}))
> and (aside from no recursive expansions) that should evaluate exactly
> the same as
> eval "((${exp}))"
> would.
>
>
> What's more, I don't see what the issue is, inside (( )) or $(( ))
> is what should be treated as a double quoted string (arith context
> for evaluation, but still a double quoted string - and the first thing
> the shell should be doing with any double quoted string, in any context,
> is to do any var/cmdsub/arith expansions that occur within it. Then
> it gets used for whatever purpose it has.
>
> Do that in the given example, and
>
> ((i=$x,a[b[i]]))
> turns into
> ((i=0,a[b[i]]))
>
> which does work. Of course, I know nothing about how any of this
> is implemented inside bash, but this just seems simple to me, and
> if as:
>
>
> chet.ra...@case.edu said:
> | This was one of the results of this 2021 discussion:
> | https://lists.gnu.org/archive/html/bug-bash/2021-03/msg00056.html
> | You can get the result you want by not using the $.
>
> then something went very badly wrong with what happened there, and
> simply saying "don't use the $" is not nearly good enough.
>
> kre
>
>
>
>
