Re: Use of $@

[Andreas Kusalananda Kähäri]

On Tue, Feb 21, 2023 at 11:27:36AM +0100, Christof Warlich wrote:
> Hi,
> 
> just to improve my bash skills: The following functions prints the array
> index of a value if found:
> 
> index() { local e="$1"; shift; local a=("$@"); for i in "${!a[@]}"; do
> [[ ${a[$i]} != $e ]] || { echo $i; break; }; done; }
> 
> Thus, with e.g.: myarray=("a" "bc" "my value" "z")
> 
> I get:
> 
> $ index "my value" "${myarray[@]}"
> 2
> 
> as expected. The only thing that bothers me is that I couldn't get away
> without the intermediate assignment of $@ to a new array (a): Is there
> really no way to avoid that, i.e. directly using $@ in the for-loop?
> 
> Cheers,
> 
> Chris

You don't have to mention $@ at all, just shift elements off from the
list until you find the one you're looking for, or until the list is
empty. The below implementation returns a non-zero exit status (and no
output) if the string isn't found.

index () {
        local query="$1"; shift
        local index=0

        until [ "$#" -eq 0 ] || [ "$1" = "$query" ]
        do
                index=$(( index + 1 ))
                shift
        done

        [ "$#" -ne 0 ] && printf '%s\n' "$index"
}

arr=( a bc "my value" z )

if ! index "my value" "${arr[@]}"
then
        echo 'not found' >&2
fi

-- 
Andreas (Kusalananda) Kähäri
SciLifeLab, NBIS, ICM
Uppsala University, Sweden

.