yq/mkdocs/merge.md

Yaml files can be merged using the 'merge' command. Each additional file merged with the first file will set values for any key not existing already or where the key has no value.

yq m <yaml_file> <path>...

Merge example

Given a data1.yaml file of:

a: simple
b: [1, 2]

and data2.yaml file of:

a: other
c:
  test: 1

then

yq m data1.yaml data2.yaml

will output:

a: simple
b: [1, 2]
c:
  test: 1

Updating files in-place

yq m -i data1.yaml data2.yaml

will update the data1.yaml file with the merged result.

Overwrite values

Given a data1.yaml file of:

a: simple
b: [1, 2]

and data2.yaml file of:

a: other
c:
  test: 1

then

yq m -x data1.yaml data2.yaml

will output:

a: other
b: [1, 2]
c:
  test: 1

Overwrite values with arrays

Given a data1.yaml file of:

a: simple
b: [1, 2]

and data3.yaml file of:

b: [3, 4]
c:
  test: 2
  other: true
d: false

then

yq m -x data1.yaml data3.yaml

will output:

a: simple
b: [3, 4]
c:
  test: 2
  other: true
d: false

Notice that 'b' does not result in the merging of the values within an array.

Append values with arrays

Given a data1.yaml file of:

a: simple
b: [1, 2]
d: hi

and data3.yaml file of:

a: something
b: [3, 4]
c:
  test: 2
  other: true

then

yq m -a data1.yaml data3.yaml

will output:

a: simple
b: [1, 2, 3, 4]
c:
  test: 2
  other: true
d: hi

Note that the 'b' array has concatenated the values from the second data file. Also note that other map keys are not overridden (field a).

Multiple Documents

Merge into single document

Currently yq only has multi-document support for the first document being merged into. The remaining yaml files will have their first document selected.

Given a data1.yaml file of:

something: else
---
a: simple
b: cat

and data3.yaml file of:

b: dog

then

yq m -x -d1 data1.yaml data3.yaml

will output:

something: else
---
a: simple
b: dog

Merge into all documents

Currently yq only has multi-document support for the first document being merged into. The remaining yaml files will have their first document selected.

Given a data1.yaml file of:

something: else
---
a: simple
b: cat

and data3.yaml file of:

b: dog

then

yq m -x -d'*' data1.yaml data3.yaml

will output:

b: dog
something: else
---
a: simple
b: dog