docs/howto: export specific elements in a top-level list

[jpluscplusm]

We have the pages https://cuelang.org/docs/howto/export-fields-whose-names-are-not-valid-identifiers/ and https://cuelang.org/docs/howto/refer-to-fields-whose-names-are-not-valid-identifiers/, but they don't explicitly mention how the elements of a top-level list can be accessed.

Show an example like this on a separate page, but where

exec cue export list.json -l input: -e 'input[1]'
-- list.json --
[ 1, "2", 3 ]

This page will exist to demonstrate the -e required. No matching page should be needed to handle the case where the reference is required inside CUE code, as that follows directly from this example and the pages mentioned above.

[myitcv]

Is there a conversation somewhere that motivated this?

[jpluscplusm]

Is there a conversation somewhere that motivated this?

No. I needed to parse some JSON output when building cuelang.org, and realised we don't cover this issue's precise use case on the site.

My specific use case

$ ip -json r g 8.8.8.8 
[{"dst":"8.8.8.8","gateway":"192.168.0.1","dev":"eth0","prefsrc":"192.168.0.200","flags":[],"uid":1100,"cache":[]}]
$ IP=$(ip -json r g 8.8.8.8 | cue export json: - --path input: --expression 'input[0].prefsrc' --out text)
$ ./scripts/serve.bash --update --hugo=--bind=0.0.0.0 --hugo=--baseURL=http://$IP:1313
...