yq/pkg/yqlib/doc/multiply-merge.md

Multiply (Merge)

Like the multiple operator in jq, depending on the operands, this multiply operator will do different things. Currently numbers, arrays and objects are supported.

Objects and arrays - merging

Objects are merged deeply matching on matching keys. By default, array values override and are not deeply merged.

Note that when merging objects, this operator returns the merged object (not the parent). This will be clearer in the examples below.

Merge Flags

You can control how objects are merged by using one or more of the following flags. Multiple flags can be used together, e.g. .a *+? .b. See examples below

• + to append arrays
• ? to only merge existing fields
• d to deeply merge arrays

Merging files

Note the use of eval-all to ensure all documents are loaded into memory.

yq eval-all 'select(fileIndex == 0) * select(fileIndex == 1)' file1.yaml file2.yaml

Multiply integers

Running

yq eval --null-input '3 * 4'

will output

12

Merge objects together, returning merged result only

Given a sample.yml file of:

a:
  field: me
  fieldA: cat
b:
  field:
    g: wizz
  fieldB: dog

then

yq eval '.a * .b' sample.yml

will output

field:
  g: wizz
fieldA: cat
fieldB: dog

Merge objects together, returning parent object

Given a sample.yml file of:

a:
  field: me
  fieldA: cat
b:
  field:
    g: wizz
  fieldB: dog

then

yq eval '. * {"a":.b}' sample.yml

will output

a:
  field:
    g: wizz
  fieldA: cat
  fieldB: dog
b:
  field:
    g: wizz
  fieldB: dog

Merge keeps style of LHS

Given a sample.yml file of:

a: {things: great}
b:
  also: "me"

then

yq eval '. * {"a":.b}' sample.yml

will output

a: {things: great, also: "me"}
b:
  also: "me"

Merge arrays

Given a sample.yml file of:

a:
  - 1
  - 2
  - 3
b:
  - 3
  - 4
  - 5

then

yq eval '. * {"a":.b}' sample.yml

will output

a:
  - 3
  - 4
  - 5
b:
  - 3
  - 4
  - 5

Merge, only existing fields

Given a sample.yml file of:

a:
  thing: one
  cat: frog
b:
  missing: two
  thing: two

then

yq eval '.a *? .b' sample.yml

will output

thing: two
cat: frog

Merge, appending arrays

Given a sample.yml file of:

a:
  array:
    - 1
    - 2
    - animal: dog
  value: coconut
b:
  array:
    - 3
    - 4
    - animal: cat
  value: banana

then

yq eval '.a *+ .b' sample.yml

will output

array:
  - 1
  - 2
  - animal: dog
  - 3
  - 4
  - animal: cat
value: banana

Merge, only existing fields, appending arrays

Given a sample.yml file of:

a:
  thing:
    - 1
    - 2
b:
  thing:
    - 3
    - 4
  another:
    - 1

then

yq eval '.a *?+ .b' sample.yml

will output

thing:
  - 1
  - 2
  - 3
  - 4

Merge, deeply merging arrays

Merging arrays deeply means arrays are merge like objects, with indexes as their key. In this case, we merge the first item in the array, and do nothing with the second.

Given a sample.yml file of:

a:
  - name: fred
    age: 12
  - name: bob
    age: 32
b:
  - name: fred
    age: 34

then

yq eval '.a *d .b' sample.yml

will output

- name: fred
  age: 34
- name: bob
  age: 32

Merge arrays of objects together, matching on a key

It's a complex command, the trickyness comes from needing to have the right context in the expressions. First we save the second array into a variable '$two' which lets us reference it later. We then need to update the first array. We will use the relative update (|=) because we need to update relative to the current element of the array in the LHS in the RHS expression. We set the current element of the first array as $cur. Now we multiply (merge) $cur with the matching entry in $two, by passing $two through a select filter.

Given a sample.yml file of:

- a: apple
  b: appleB
- a: kiwi
  b: kiwiB
- a: banana
  b: bananaB

And another sample another.yml file of:

- a: banana
  c: bananaC
- a: apple
  b: appleB2
- a: dingo
  c: dingoC

then

yq eval-all '(select(fi==1) | .[]) as $two | select(fi==0) | .[] |= (. as $cur |  $cur * ($two | select(.a == $cur.a)))' sample.yml another.yml

will output

- a: apple
  b: appleB2
- a: kiwi
  b: kiwiB
- a: banana
  b: bananaB
  c: bananaC

Merge to prefix an element

Given a sample.yml file of:

a: cat
b: dog

then

yq eval '. * {"a": {"c": .a}}' sample.yml

will output

a:
  c: cat
b: dog

Merge with simple aliases

Given a sample.yml file of:

a: &cat
  c: frog
b:
  f: *cat
c:
  g: thongs

then

yq eval '.c * .b' sample.yml

will output

g: thongs
f: *cat

Merge copies anchor names

Given a sample.yml file of:

a:
  c: &cat frog
b:
  f: *cat
c:
  g: thongs

then

yq eval '.c * .a' sample.yml

will output

g: thongs
c: &cat frog

Merge with merge anchors

Given a sample.yml file of:

foo: &foo
  a: foo_a
  thing: foo_thing
  c: foo_c
bar: &bar
  b: bar_b
  thing: bar_thing
  c: bar_c
foobarList:
  b: foobarList_b
  !!merge <<:
    - *foo
    - *bar
  c: foobarList_c
foobar:
  c: foobar_c
  !!merge <<: *foo
  thing: foobar_thing

then

yq eval '.foobar * .foobarList' sample.yml

will output

c: foobarList_c
!!merge <<:
  - *foo
  - *bar
thing: foobar_thing
b: foobarList_b