[naniwaduni]

> The leading "{}" is moderately necessary because `jq` technically _processes_ json, not generates it.

The --null-input/-n option is the "out-of-the-box" way to achieve this, and avoids a pipe (usually not a big deal, but leaves stdin free and sometimes saves a fork).

This lets you rewrite your first "pattern":

    jq -cnr --argjson SOME_JSON "$SOME_JSON" '$SOME_JSON[]' | while read ...

We also have a "useless use of cat": --slurpfile does that job better:

    jq -n --slurpfile FOO test.json '{bar: $FOO[]}'

(assuming you are assured that test.json contains one json value; --argjson will immediately fail if this is not the case, but with --slurpjson you may need to check that $FOO is a 1-item array.)

And of course, for exactly the single-file single-object case, you can just write:

    jq '{bar: .}' test.json

[ramses0]

Prefer long args in all cases, especially scripts and teaching.

Pipelines allow consistent syntax, but thanks for pointing out all the different variations of file support in jq.