Alternative (Default value)

This operator is used to provide alternative (or default) values when a particular expression is either null or false.

LHS is defined

Given a sample.yml file of:

yaml

a: bridge

then

bash

yq '.a // "hello"' sample.yml

will output

yaml

bridge

LHS is not defined

Given a sample.yml file of:

yaml

{}

then

bash

yq '.a // "hello"' sample.yml

will output

yaml

hello

LHS is null

Given a sample.yml file of:

yaml

a: ~

then

bash

yq '.a // "hello"' sample.yml

will output

yaml

hello

LHS is false

Given a sample.yml file of:

yaml

a: false

then

bash

yq '.a // "hello"' sample.yml

will output

yaml

hello

RHS is an expression

Given a sample.yml file of:

yaml

a: false
b: cat

then

bash

yq '.a // .b' sample.yml

will output

yaml

cat

Update or create - entity exists

This initialises a if it's not present

Given a sample.yml file of:

yaml

a: 1

then

bash

yq '(.a // (.a = 0)) += 1' sample.yml

will output

yaml

a: 2

Update or create - entity does not exist

This initialises a if it's not present

Given a sample.yml file of:

yaml

b: camel

then

bash

yq '(.a // (.a = 0)) += 1' sample.yml

will output

yaml

b: camel
a: 1