Unfortunately, it doesn't merge/concatenate arrays. Sometimes that's what you want (you want the 2nd value to override the 1st but sometimes not.

If you want it to concatenate instead, here are some workarounds:

1. https://stackoverflow.com/questions/53661930/jq-recursively-merge-objects-and-concatenate-arrays

2. If you only need/want to concatenate for some fixed list of keys, you could do it more simply like this (but could get repetitive to repeat for each key you want it for):

⟫ jq -n '[{hosts: ["a"]}, {hosts: ["b"]}] | .[]' | jq -s '.[0] * .[1] * {hosts: (.[0].hosts + .[1].hosts)}' { "hosts": [ "a", "b" ] }