Merge only missing keys

[23tux]

First of all: Really appreciate the work on yq, it's a huge time safer for me!

This command from the docs merges everything from file2.yml into file1.yml

yq ea '. as $item ireduce ({}; . * $item)' -i file1.yml file2.yml

# file1.yml
key1: Key1
key2: Key2

# file2.yml
key1: Overwritten Key1
key3: Key3

And this is file1.yml after the merge:

# file1.yml
# file2.yml
key1: Overwritten Key1
key2: Key2
key3: Key3

My question is: Is it possible, to skip the overwrite for key1: Overwritten Key1 / is it possible to only merge new keys and not overwrite existing ones? The resulting yaml should look like this:

# file1.yml
# file2.yml
key1: Key1
key2: Key2
key3: Key3

[mikefarah]

Yep - documented here: https://mikefarah.gitbook.io/yq/operators/multiply-merge#merge-flags

[mikefarah]

oh wait - you want the opposite right? only include new field and leave the existing 🤔

[23tux]

yes, I only want to include new fields and the leave the existing ones as they are. So basically, the opposite of the ? flag:

? to only merge existing fields

[mikefarah]

Will have this functionality out (and documented) in the next release (next weekend eta)

[mikefarah]

Ok I've released a new merge flag (n) https://mikefarah.gitbook.io/yq/operators/multiply-merge#merge-only-new-fields in 4.17.2 :)

yq ea '. as $item ireduce ({}; . *n $item)' examples/data1.yaml examples/data2.yaml

key1: Key1
key2: Key2
key3: Key3