jq combine json files into single array

Question

I have several json files I want to combine. Some are arrays of objects and some are single objects. I want to effectively concatenate all of this into a single array.

For example:

[ { "name": "file1" } ]

{ "name": "file2" }

{ "name": "file3" }

And I want to end up with:

[ { "name": "file1" } { "name": "file2" }, { "name": "file3" }, ]

How can I do this using jq or similar?

I believe this does it: jq -n '[inputs] | add' $(find . -name '*.json') > combined.json — drobert
– drobert, Commented Mar 2, 2021 at 16:33

peak · Accepted Answer · 2021-03-02 19:58:41Z

The following illustrates an efficient way to accomplish the required task:

jq -n 'reduce inputs as $in (null; . + if $in|type == "array" then $in else [$in] end) ' $(find . -name '*.json') > combined.json

The -n command-line option is necessary to avoid skipping the first file.

drobert · Accepted Answer · 2021-03-02 16:37:32Z

0

This did it:

jq -n '[inputs] | add' $(find . -name '*.json') > combined.json

answered Mar 2, 2021 at 16:37

drobert

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6 Comments

peak Over a year ago

Alas, this is incorrect, and also an inefficient way to do what it does.

drobert Over a year ago

Can you offer context on why this is 'incorrect'? It seems to work, what is incorrect about it?

peak Over a year ago

Your requirements differentiate between files with an array and those with a top-level JSON object. Have you tried your own example? Please also compare with my answer.

drobert Over a year ago

Yes I have. I have a resulting file that is a single array where all inner types have been flattened. I have experienced no issues so far. I'm not sure how I would 'compare'. I would expect both to give me what I described. Unless there's a counterexample (or you can give me some details on why one is 'incorrect', which I'd genuinely appreciate) I'm not sure what I'm comparing. Why is your answer superior? (Asking out of genuine ignorance.)

peak Over a year ago

I meant compare the logic. I used your example with three files.

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