Saving $! (process ID of last background command) as an array element

Question

I can't understand the way zsh 5.9 behaves when assigning $! to an array:

unset a b c

sleep 3 &

a=$!
b[1]=$!
c[1]=${!}

typeset -p a b c

output:

typeset a=21391
typeset -a b=( '$!' )
typeset -a c=( 21391 )

Getting b=( '$!' ) doesn't feel right... Is it a feature? A regression?

On Linux I get b=( 20769 ) with zsh 5.0.2 and b=( '$!' ) with zsh 5.5.1. — Fravadona
– Fravadona, Commented Aug 14, 2024 at 15:12
b[1]="$!" works as expected, too. It's just the bare case. Weird. — Shawn
– Shawn, Commented Aug 14, 2024 at 21:25
I was testing with 5.9; didn't get the unmatched error.... I bet it has something to do with history expansion, since ! is used for that. — Shawn
– Shawn, Commented Aug 15, 2024 at 5:33

Fravadona · Accepted Answer · 2024-11-15 18:42:09Z

1

The problem's been fixed in commit 5977d3c

But IMHO it's best not to rely on arr[1]=$! anymore and use the following workaround to be portable across zsh versions:

arr[1]=${!}

answered Aug 20, 2024 at 10:36

Fravadona

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