Assign (Update)

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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.
Create yaml file
Running
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yq eval --null-input '.a.b = "cat" | .x = "frog"'
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will output
1
a:
2
  b: cat
3
x: frog
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Update node to be the child value
Given a sample.yml file of:
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a:
2
  b:
3
    g: foof
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then
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yq eval '.a |= .b' sample.yml
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will output
1
a:
2
  g: foof
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Double elements in an array
Given a sample.yml file of:
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- 1
2
- 2
3
- 3
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then
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yq eval '.[] |= . * 2' sample.yml
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will output
1
- 2
2
- 4
3
- 6
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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:
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a: apples
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And another sample another.yml file of:
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b: bob
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then
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yq eval-all 'select(fileIndex==0).a = select(fileIndex==1) | select(fileIndex==0)' sample.yml another.yml
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will output
1
a:
2
  b: bob
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Update node to be the sibling value
Given a sample.yml file of:
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a:
2
  b: child
3
b: sibling
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then
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yq eval '.a = .b' sample.yml
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will output
1
a: sibling
2
b: sibling
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Updated multiple paths
Given a sample.yml file of:
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a: fieldA
2
b: fieldB
3
c: fieldC
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then
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yq eval '(.a, .c) = "potatoe"' sample.yml
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will output
1
a: potatoe
2
b: fieldB
3
c: potatoe
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Update string value
Given a sample.yml file of:
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a:
2
  b: apple
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then
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yq eval '.a.b = "frog"' sample.yml
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will output
1
a:
2
  b: frog
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Update string value via |=
Note there is no difference between = and |= when the RHS is a scalar
Given a sample.yml file of:
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a:
2
  b: apple
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then
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yq eval '.a.b |= "frog"' sample.yml
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will output
1
a:
2
  b: frog
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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:
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a:
2
  b: apple
3
  c: cactus
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then
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yq eval '(.a[] | select(. == "apple")) = "frog"' sample.yml
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will output
1
a:
2
  b: frog
3
  c: cactus
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Update array values
Given a sample.yml file of:
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- candy
2
- apple
3
- sandy
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then
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yq eval '(.[] | select(. == "*andy")) = "bogs"' sample.yml
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will output
1
- bogs
2
- apple
3
- bogs
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Update empty object
Given a sample.yml file of:
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{}
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then
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yq eval '.a.b |= "bogs"' sample.yml
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will output
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{a: {b: bogs}}
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Update node value that has an anchor
Anchor will remaple
Given a sample.yml file of:
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a: &cool cat
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then
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yq eval '.a = "dog"' sample.yml
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will output
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a: &cool dog
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Update empty object and array
Given a sample.yml file of:
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{}
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then
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yq eval '.a.b.[0] |= "bogs"' sample.yml
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will output
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{a: {b: [bogs]}}
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