How to merge 2 JSON objects from 2 files using jq?

Since 1.4 this is now possible with the * operator. When given two objects, it will merge them recursively. For example,

jq -s '.[0] * .[1]' file1 file2

Important: Note the -s (--slurp) flag, which puts files in the same array.

Would get you:

{  "value1": 200,  "timestamp": 1382461861,  "value": {    "aaa": {      "value1": "v1",      "value2": "v2",      "value3": "v3",      "value4": 4    },    "bbb": {      "value1": "v1",      "value2": "v2",      "value3": "v3"    },    "ccc": {      "value1": "v1",      "value2": "v2"    },    "ddd": {      "value3": "v3",      "value4": 4    }  },  "status": 200}

If you also want to get rid of the other keys (like your expected result), one way to do it is this:

jq -s '.[0] * .[1] | {value: .value}' file1 file2

Or the presumably somewhat more efficient (because it doesn't merge any other values):

jq -s '.[0].value * .[1].value | {value: .}' file1 file2

Use jq -s add:

$ echo '{"a":"foo","b":"bar"} {"c":"baz","a":0}' | jq -s add{  "a": 0,  "b": "bar",  "c": "baz"}

This reads all JSON texts from stdin into an array (jq -s does that) then it "reduces" them.

(add is defined as def add: reduce .[] as $x (null; . + $x);, which iterates over the input array's/object's values and adds them. Object addition == merge.)

Who knows if you still need it, but here is the solution.

Once you get to the --slurp option, it's easy!

--slurp/-s:    Instead of running the filter for each JSON object in the input,    read the entire input stream into a large array and run the filter just once.

Then the + operator will do what you want:

jq -s '.[0] + .[1]' config.json config-user.json

(Note: if you want to merge inner objects instead of just overwriting the left file ones with the right file ones, you will need to do it manually)