yq/pkg/yqlib/doc/operators/anchor-and-alias-operators.md

Anchor and Alias Operators

Use the alias and anchor operators to read and write yaml aliases and anchors. The explode operator normalises a yaml file (dereference (or expands) aliases and remove anchor names).

yq supports merge aliases (like <<: *blah) however this is no longer in the standard yaml spec (1.2) and so yq will automatically add the !!merge tag to these nodes as it is effectively a custom tag.

Merge one map

see https://yaml.org/type/merge.html

Given a sample.yml file of:

- &CENTER
  x: 1
  y: 2
- &LEFT
  x: 0
  y: 2
- &BIG
  r: 10
- &SMALL
  r: 1
- !!merge <<: *CENTER
  r: 10

then

yq '.[4] | explode(.)' sample.yml

will output

x: 1
y: 2
r: 10

Merge multiple maps

see https://yaml.org/type/merge.html

Given a sample.yml file of:

- &CENTER
  x: 1
  y: 2
- &LEFT
  x: 0
  y: 2
- &BIG
  r: 10
- &SMALL
  r: 1
- !!merge <<:
    - *CENTER
    - *BIG

then

yq '.[4] | explode(.)' sample.yml

will output

r: 10
x: 1
y: 2

Override

see https://yaml.org/type/merge.html

Given a sample.yml file of:

- &CENTER
  x: 1
  y: 2
- &LEFT
  x: 0
  y: 2
- &BIG
  r: 10
- &SMALL
  r: 1
- !!merge <<:
    - *BIG
    - *LEFT
    - *SMALL
  x: 1

then

yq '.[4] | explode(.)' sample.yml

will output

r: 10
x: 1
y: 2

Get anchor

Given a sample.yml file of:

a: &billyBob cat

then

yq '.a | anchor' sample.yml

will output

billyBob

Set anchor

Given a sample.yml file of:

a: cat

then

yq '.a anchor = "foobar"' sample.yml

will output

a: &foobar cat

Set anchor relatively using assign-update

Given a sample.yml file of:

a:
  b: cat

then

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

will output

a: &cat
  b: cat

Get alias

Given a sample.yml file of:

{b: &billyBob meow, a: *billyBob}

then

yq '.a | alias' sample.yml

will output

billyBob

Set alias

Given a sample.yml file of:

{b: &meow purr, a: cat}

then

yq '.a alias = "meow"' sample.yml

will output

{b: &meow purr, a: *meow}

Set alias to blank does nothing

Given a sample.yml file of:

{b: &meow purr, a: cat}

then

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

will output

{b: &meow purr, a: cat}

Set alias relatively using assign-update

Given a sample.yml file of:

{b: &meow purr, a: {f: meow}}

then

yq '.a alias |= .f' sample.yml

will output

{b: &meow purr, a: *meow}

Explode alias and anchor

Given a sample.yml file of:

{f: {a: &a cat, b: *a}}

then

yq 'explode(.f)' sample.yml

will output

{f: {a: cat, b: cat}}

Explode with no aliases or anchors

Given a sample.yml file of:

a: mike

then

yq 'explode(.a)' sample.yml

will output

a: mike

Explode with alias keys

Given a sample.yml file of:

{f: {a: &a cat, *a: b}}

then

yq 'explode(.f)' sample.yml

will output

{f: {a: cat, cat: b}}

Explode with merge anchors

Given a sample.yml file of:

foo: &foo
  a: foo_a
  thing: foo_thing
  c: foo_c
bar: &bar
  b: bar_b
  thing: bar_thing
  c: bar_c
foobarList:
  b: foobarList_b
  !!merge <<:
    - *foo
    - *bar
  c: foobarList_c
foobar:
  c: foobar_c
  !!merge <<: *foo
  thing: foobar_thing

then

yq 'explode(.)' sample.yml

will output

foo:
  a: foo_a
  thing: foo_thing
  c: foo_c
bar:
  b: bar_b
  thing: bar_thing
  c: bar_c
foobarList:
  b: bar_b
  thing: foo_thing
  c: foobarList_c
  a: foo_a
foobar:
  c: foo_c
  a: foo_a
  thing: foobar_thing

Dereference and update a field

Use explode with multiply to dereference an object

Given a sample.yml file of:

item_value: &item_value
  value: true
thingOne:
  name: item_1
  !!merge <<: *item_value
thingTwo:
  name: item_2
  !!merge <<: *item_value

then

yq '.thingOne |= explode(.) * {"value": false}' sample.yml

will output

item_value: &item_value
  value: true
thingOne:
  name: item_1
  value: false
thingTwo:
  name: item_2
  !!merge <<: *item_value