yq/pkg/yqlib/doc/operators/add.md

Add

Add behaves differently according to the type of the LHS:

• arrays: concatenate
• number scalars: arithmetic addition
• string scalars: concatenate
• maps: shallow merge (use the multiply operator (*) to deeply merge)

Use += as a relative append assign for things like increment. Note that .a += .x is equivalent to running .a = .a + .x.

Concatenate arrays

Given a sample.yml file of:

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

then

yq '.a + .b' sample.yml

will output

- 1
- 2
- 3
- 4

Concatenate to existing array

Note that the styling of a is kept.

Given a sample.yml file of:

a: [1,2]
b:
  - 3
  - 4

then

yq '.a += .b' sample.yml

will output

a: [1, 2, 3, 4]
b:
  - 3
  - 4

Concatenate null to array

Given a sample.yml file of:

a:
  - 1
  - 2

then

yq '.a + null' sample.yml

will output

- 1
- 2

Append to existing array

Note that the styling is copied from existing array elements

Given a sample.yml file of:

a: ['dog']

then

yq '.a += "cat"' sample.yml

will output

a: ['dog', 'cat']

Add new object to array

Given a sample.yml file of:

a:
  - dog: woof

then

yq '.a + {"cat": "meow"}' sample.yml

will output

- dog: woof
- cat: meow

Relative append

Given a sample.yml file of:

a:
  a1:
    b:
      - cat
  a2:
    b:
      - dog
  a3: {}

then

yq '.a[].b += ["mouse"]' sample.yml

will output

a:
  a1:
    b:
      - cat
      - mouse
  a2:
    b:
      - dog
      - mouse
  a3: {b: [mouse]}

String concatenation

Given a sample.yml file of:

a: cat
b: meow

then

yq '.a += .b' sample.yml

will output

a: catmeow
b: meow

Number addition - float

If the lhs or rhs are floats then the expression will be calculated with floats.

Given a sample.yml file of:

a: 3
b: 4.9

then

yq '.a = .a + .b' sample.yml

will output

a: 7.9
b: 4.9

Number addition - int

If both the lhs and rhs are ints then the expression will be calculated with ints.

Given a sample.yml file of:

a: 3
b: 4

then

yq '.a = .a + .b' sample.yml

will output

a: 7
b: 4

Increment numbers

Given a sample.yml file of:

a: 3
b: 5

then

yq '.[] += 1' sample.yml

will output

a: 4
b: 6

Add to null

Adding to null simply returns the rhs

Running

yq --null-input 'null + "cat"'

will output

cat

Add maps to shallow merge

Adding objects together shallow merges them. Use * to deeply merge.

Given a sample.yml file of:

a:
  thing:
    name: Astuff
    value: x
  a1: cool
b:
  thing:
    name: Bstuff
    legs: 3
  b1: neat

then

yq '.a += .b' sample.yml

will output

a:
  thing:
    name: Bstuff
    legs: 3
  a1: cool
  b1: neat
b:
  thing:
    name: Bstuff
    legs: 3
  b1: neat

Custom types: that are really strings

When custom tags are encountered, yq will try to decode the underlying type.

Given a sample.yml file of:

a: !horse cat
b: !goat _meow

then

yq '.a += .b' sample.yml

will output

a: !horse cat_meow
b: !goat _meow

Custom types: that are really numbers

When custom tags are encountered, yq will try to decode the underlying type.

Given a sample.yml file of:

a: !horse 1.2
b: !goat 2.3

then

yq '.a += .b' sample.yml

will output

a: !horse 3.5
b: !goat 2.3