Create yaml file

Running

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

will output

a:
  g: foof

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 eval '.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 eval '(.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 eval '.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 eval '.a.b |= "frog"' sample.yml

will output

a:
  b: frog

Update selected results

Given a sample.yml file of:

a:
  b: apple
  c: cactus

then

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

will output

- bogs
- apple
- bogs

Update empty object

Given a sample.yml file of:

{}

then

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

will output

{a: {b: bogs}}

Update empty object and array

Given a sample.yml file of:

{}

then

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

will output

{a: {b: [bogs]}}