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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']

Prepend to existing array

Given a sample.yml file of:
a:
- dog
then
yq '.a = ["cat"] + .a' sample.yml
will output
a:
- cat
- dog

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

Date addition

You can add durations to dates. Assumes RFC3339 date time format, see date-time operators for more information.
Given a sample.yml file of:
a: 2021-01-01T00:00:00Z
then
yq '.a += "3h10m"' sample.yml
will output
a: 2021-01-01T03:10:00Z

Date addition - custom format

You can add durations to dates. See date-time operators for more information.
Given a sample.yml file of:
a: Saturday, 15-Dec-01 at 2:59AM GMT
then
yq 'with_dtf("Monday, 02-Jan-06 at 3:04PM MST", .a += "3h1m")' sample.yml
will output
a: Saturday, 15-Dec-01 at 6:00AM GMT

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