Bug report: assigning $! to an array element doesn't work

Bug report: assigning $! to an array element doesn't work

[Frava]

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Dear ZSH gurus,

I noticed the following problem with zsh 5.9 (macOS Sonoma, ARM M2) AND zsh
5.5.1 (Linux RHEL8 x86_64):

#!/bin/zsh
sleep 1 &
arr[1]=$!
typeset -p arr

output:

typeset -a arr=( '$!' )

The double-quoting doesn't work either:

#!/bin/zsh
sleep 1 &
arr[1]="$!"

errput:

unmatched "

---

Thank you for your support,
Rafael.

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Re: Bug report: assigning $! to an array element doesn't work

[Bart Schaefer]

On Wed, Aug 14, 2024 at 4:06 PM Frava <fravadona@gmail.com> wrote:
>
> arr[1]=$!
> typeset -p arr
>
> output:
>
> typeset -a arr=( '$!' )

Hmm, interesting.  When doing lexical analysis of an assignment to an
array element, the ! is tokenized, so $! becomes a plain string. That
can be avoided by:

% arr[1]=($!)

The oddity results from this bit of code in lex.c (pardon possible
loss of tab stop indentation):

1390        case LX2_DASH:
1391            /*
1392             * - shouldn't be treated as a special character unless
1393             * we're in a pattern.  Unfortunately, working out for
1394             * sure in complicated expressions whether we're in a
1395             * pattern is tricky.  So we'll make it special and
1396             * turn it back any time we don't need it special.
1397             * This is not ideal as it's a lot of work.
1398             */
1399            c = Dash;
1400               break;
1401        case LX2_BANG:
1402            /*
1403             * Same logic as Dash, for ! to perform negation in range.
1404             */
1405            if (seen_brct)
1406            c = Bang;
1407            else
1408            c = '!';

The trouble is that seen_brct == 1 because of encountering the open
bracket of the array subscript.  Does anyone (*cough*PWS*cough*)
recall why we need and use seen_brct there rather than just brct ?
seen_brct was introduced for Dash in workers/37678, extended to Bang
in workers/37689, then removed from Dash in workers/40760 without
addressing Bang.  The only case where seen_brct is zero while brct
might be nonzero was introduced by workers/37705.

Changing line 1405 to

1405            if (seen_brct && brct)

still passes all "make check" tests, and fixes the assignment.

> The double-quoting doesn't work either:
> unmatched "

On the other hand that one looks like you have the BANG_HIST option set.

% unsetopt banghist
% sleep 2 &
[1] 71890
% arr[1]="$!"
[1]  + done       sleep 2
% typeset -p arr
typeset -a arr=( 71890 )
% setopt banghist
% arr[1]="$!"
dquote>

However, I can't reproduce that error with a script file even with
"zsh -o banghist", for me it "fails" only at the command line.

Re: Bug report: assigning $! to an array element doesn't work

[Peter Stephenson]

> On 15/08/2024 02:16 BST Bart Schaefer <schaefer@brasslantern.com> wrote:
> Changing line 1405 to
>
> 1405            if (seen_brct && brct)
>
> still passes all "make check" tests, and fixes the assignment.

Without an explicit test for the problem cases inolved to guide us further,
that's probably good enough.  It's not obviously wrong and any problem
is going to be obscure.

pws