[COFF] Re: On Bloat and the Idea of Small Specialized Tools

[Ralph Corderoy <ralph@inputplus.co.uk>]

Hi,

As an example of pushing the limit of Unix pipes, I found this awkward
to read, e.g. the noise of the redundant backslash after an end-of-line
pipe.

>             gcloud compute instances describe \
>                         --zone "$z" "$i" --format=json > "$inst_info"
>             kver=$(jq < "$inst_info" 2> /dev/null \
>                 '.metadata.items[] | select(.key == "kernel_version") | .value' | \
>                         sed -e 's/^"//' -e 's/"$//' \
>                             -e 's/^Linux xfstests-[0-9A-Za-z-]* //' -e 's/ .*//')
> `           gce_status=$(jq < "$inst_info" .status | \
>                             sed -e 's/^"//' -e 's/"$//')
>             status=$(jq < "$inst_info" 2> /dev/null \
>                 '.metadata.items[] | select(.key == "status") | .value' | \
>                             sed -e 's/^"//' -e 's/"$//')
>             ip=$(jq < "$inst_info" 2> /dev/null \
>                     '.networkInterfaces[] | .accessConfigs[] | select(.name == "external-nat") | .natIP' | \
>                         sed -e 's/^"//' -e 's/"$//')

Re-formatting, including the more idiomatic placement of I/O
redirection, gives

    gcloud compute instances describe \
        --zone "$z" "$i" --format=json >"$inst_info"

    kver=$(
        jq '.metadata.items[] | select(.key == "kernel_version") | .value' \
            <"$inst_info" 2>/dev/null |
        sed '
                s/^"//; s/"$//
                s/^Linux xfstests-[0-9A-Za-z-]* //
                s/ .*//
            '
    )
    gce_status=$(
        jq .status \
            <"$inst_info" |
        sed 's/^"//; s/"$//'
    )
    status=$(
        jq '.metadata.items[] | select(.key == "status") | .value' \
            <"$inst_info" 2>/dev/null |
        sed 's/^"//; s/"$//'
    )
    ip=$(
        jq '.networkInterfaces[] | .accessConfigs[] | select(.name == "external-nat") | .natIP' \
            <"$inst_info" 2>/dev/null |
        sed 's/^"//; s/"$//'
    )

The repetition is now more clear to me.  And I see jq's stderr is
discarded in all but one case.  Assuming that one can be, or should be,
the same allows factoring.

    gcloud compute instances describe \
        --zone "$z" "$i" --format=json >"$inst_info"

    query() {
        jq "${1?}" <"$inst_info" 2>/dev/null |
        sed 's/^"//; s/"$//'
    }

    kver=$(
        query '.metadata.items[] | select(.key == "kernel_version") | .value' |
        sed 's/^Linux xfstests-[0-9A-Za-z-]* //; s/ .*//'
    )
    gce_status=$(query .status)
    status=$(query '.metadata.items[] | select(.key == "status") | .value')
    ip=$(query '.networkInterfaces[] | .accessConfigs[] | select(.name == "external-nat") | .natIP')

-- 
Cheers, Ralph.