This is used to construct objects (or maps). This can be used against existing yaml, or to create fresh yaml documents.

Collect empty object

Running

yq eval --null-input '{}'

will output

{}

Wrap (prefix) existing object

Given a sample.yml file of:

name: Mike

then

yq eval '{"wrap": .}' sample.yml

will output

wrap:
  name: Mike

Using splat to create multiple objects

Given a sample.yml file of:

name: Mike
pets:
  - cat
  - dog

then

yq eval '{.name: .pets.[]}' sample.yml

will output

Mike: cat
Mike: dog

Working with multiple documents

Given a sample.yml file of:

name: Mike
pets:
  - cat
  - dog
---
name: Rosey
pets:
  - monkey
  - sheep

then

yq eval '{.name: .pets.[]}' sample.yml

will output

Mike: cat
Mike: dog
Rosey: monkey
Rosey: sheep

Creating yaml from scratch

Running

yq eval --null-input '{"wrap": "frog"}'

will output

wrap: frog