How to merge two JSON files using jq?

Question

I need to merge two JSON files into one. The requirement is to replace values of keys existing in both files by values from second file. And add keys doesn't exist in first should be appended to the output JSON.

Is it possible to use jq to perform this operation?

First JSON:

{
    "foo": "bar",
    "aaa": "aaa",
    "count": 0
}

Second JSON:

{
    "bbb": "bbb",
    "count": 1
}

Expected output:

{
    "foo": "bar",
    "aaa": "aaa",
    "count": 1,
    "bbb": "bbb"
}

`jq '. + input' first.json second.json` (use `*` instead of `+` if you need nesting). — pmf, Mar 09 '22 at 15:41
(Interestingly, `jq -n 'input + input' first.json second.json` does *not* work; it seems to read `second.json` first.) — chepner, Mar 09 '22 at 15:44
Another answer is here: https://stackoverflow.com/questions/19529688/how-to-merge-2-json-objects-from-2-files-using-jq — fukanchik, Mar 09 '22 at 15:44
@chepner - jq and gojq differ in the order of evaluation of the arguments to `+`. For jq you could write: `input as $a | $a + input` — peak, Mar 09 '22 at 19:02

score -1 · Answer 1 · answered Mar 09 '22 at 15:52

jq provides “object multiplication” feature:

jq '. * input' file1.json file2.json

See the manual:

Multiplication, division, modulo: *, /, and %

[…]

Multiplying two objects will merge them recursively: this works like addition but if both objects contain a value for the same key, and the values are objects, the two are merged with the same strategy.

How to merge two JSON files using jq?

1 Answers1

Multiplication, division, modulo: *, /, and %