Merging file without changing array value

[steenstra]

When given the files a.yaml and b.yaml:

a.yaml

filled-in: custom_client_value
something:
 - a
 - b
something2: [a, b,]

b.yaml

filled-in: default_value
something: default_value
something2: 
  - default
  - value
this_is_a_new_value: spiksplinternieuw

I want to use yq to merge the files into:

c.yaml

filled-in: custom_client_value
something:
 - a
 - b
someting2: [a, b]
this_is_a_new_value: spiksplinternieuw

So line 1 tm 5 should stay like in a.yaml, but the new value spiksplinternieuw should be added. Basically, I want yq to only add the missing values, but not change any existing ones.

However, what happens, is this:

(v3) - yq merge --comments overwrite a.yaml b.yaml

results in

filled-in: custom_client_value
something: default_value
something2: 
  - default
  - value
this_is_a_new_value: spiksplinternieuw

When consulting the (v3) help function, it shows:

Flags:
  -a, --arrays string     array merge strategy (update/append/overwrite)
                          update: recursively update arrays by their index
                          append: concatenate arrays together
                          overwrite: replace arrays

It seems there's not an easy way for keeping the arrays as they are, like there is with all other values. Or am I missing something?

[steenstra]

Using version 4, I've resolved the issue with the following command:

docker run --rm -v "${PWD}":/workdir mikefarah/yq:latest 
eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' b.yaml a.yaml

It was not very clear from the upgrade guide that the arguments have become reversed in this version, so that b.yaml is overwritten by a.yaml.