yq/pkg/yqlib/doc/operators/assign-update.md

Assign (Update)

This operator is used to update node values. It can be used in either the:

plain form: =

Which will assign the LHS node values to the RHS node values. The RHS expression is run against the matching nodes in the pipeline.

relative form: |=

This will do a similar thing to the plain form, however, the RHS expression is run against the LHS nodes. This is useful for updating values based on old values, e.g. increment. {% hint style="warning" %} Note that versions prior to 4.18 require the 'eval/e' command to be specified.

yq e <exp> <file> {% endhint %}

Create yaml file

Running

yq --null-input '.a.b = "cat" | .x = "frog"'

will output

a:
  b: cat
x: frog

Update node to be the child value

Given a sample.yml file of:

a:
  b:
    g: foof

then

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

will output

a:
  g: foof

Double elements in an array

Given a sample.yml file of:

- 1
- 2
- 3

then

yq '.[] |= . * 2' sample.yml

will output

- 2
- 4
- 6

Update node from another file

Note this will also work when the second file is a scalar (string/number)

Given a sample.yml file of:

a: apples

And another sample another.yml file of:

b: bob

then

yq eval-all 'select(fileIndex==0).a = select(fileIndex==1) | select(fileIndex==0)' sample.yml another.yml

will output

a:
  b: bob

Update node to be the sibling value

Given a sample.yml file of:

a:
  b: child
b: sibling

then

yq '.a = .b' sample.yml

will output

a: sibling
b: sibling

Updated multiple paths

Given a sample.yml file of:

a: fieldA
b: fieldB
c: fieldC

then

yq '(.a, .c) = "potatoe"' sample.yml

will output

a: potatoe
b: fieldB
c: potatoe

Update string value

Given a sample.yml file of:

a:
  b: apple

then

yq '.a.b = "frog"' sample.yml

will output

a:
  b: frog

Update string value via |=

Note there is no difference between = and |= when the RHS is a scalar

Given a sample.yml file of:

a:
  b: apple

then

yq '.a.b |= "frog"' sample.yml

will output

a:
  b: frog

Update deeply selected results

Note that the LHS is wrapped in brackets! This is to ensure we dont first filter out the yaml and then update the snippet.

Given a sample.yml file of:

a:
  b: apple
  c: cactus

then

yq '(.a[] | select(. == "apple")) = "frog"' sample.yml

will output

a:
  b: frog
  c: cactus

Update array values

Given a sample.yml file of:

- candy
- apple
- sandy

then

yq '(.[] | select(. == "*andy")) = "bogs"' sample.yml

will output

- bogs
- apple
- bogs

Update empty object

Given a sample.yml file of:

{}

then

yq '.a.b |= "bogs"' sample.yml

will output

a:
  b: bogs

Update node value that has an anchor

Anchor will remaple

Given a sample.yml file of:

a: &cool cat

then

yq '.a = "dog"' sample.yml

will output

a: &cool dog

Update empty object and array

Given a sample.yml file of:

{}

then

yq '.a.b.[0] |= "bogs"' sample.yml

will output

a:
  b:
    - bogs