Re: Not to set PIPESTATUS unless necessary

[Kerin Millar]

On Thu, 9 May 2024, at 4:34 AM, Peng Yu wrote:
> On Wed, May 8, 2024 at 9:23 PM Kerin Millar <kfm@plushkava.net> wrote:
>>
>> On Thu, 9 May 2024, at 2:57 AM, Peng Yu wrote:
>> > Hi,
>> >
>> > true | true
>> > false
>> > echo ${PIPESTATUS[@]}
>> >
>> > In the above commands, echo will print 1. But such information is also
>> > available in $?. Therefore, I think it is unnecessary to set
>> > PIPESTATUS after false. It is better to preserve its value until it is
>>
>> Bear in mind that "false" is also a foreground pipeline there.
>>
>> > really necessary. Otherwise, users will have to preserve PIPESTATUS
>> > after running true | true. This will result in more code to write.
>>
>> Can you show a realistic program in which it necessitates significantly more 
>> code?
>
> Here is a reasonably real application.
>
> curl url | jq something || {
>  pipestatus=(${PIPESTATUS[@]})
>  # A few lines of code to consolidate the exit statuses of curl and jq
> into a single exit statute of the pipeline.
> }
>
> curl has many exit statuses. jq also has several exit statuses. It
> requires a few lines of code to preserve all the exit status info from
> both programs. Thus, not having to save PIPESTATUS to pipestatus will
> make the above scenario more compact and more readable.
>
> When similar pipelines are used a lot, it would save a lot of
> redundant code for not having to save PIPESTATUS.

OK. Given that bash can't presently do as you wish, encapsulating all of this 
within a function might then help you.

curl2jq() {
        local curl_args pipestatus
        while (( $# )); do
                curl_args+=("$1")
                shift
                if [[ $1 == -- ]]; then
                        shift
                        break
                fi
        done
        if ! curl "${curl_args[@]}" | jq "$@"; then
                pipestatus=("${PIPESTATUS[@]}") 
                : consolidation code that returns the desired value
        fi
}

curl2jq "$url" -- 'jq program'

-- 
Kerin Millar