This operator is used to handle environment variables usage in path expressions. While environment variables can, of course, be passed in via your CLI with string interpolation, this often comes with complex quote escaping and can be tricky to write and read. Note that there are two forms, env which will parse the environment variable as a yaml (be it a map, array, string, number of boolean) and strenv which will always parse the argument as a string.

Read string environment variable

Running

myenv="cat meow" yq eval --null-input '.a = env(myenv)'

will output

a: cat meow

Read boolean environment variable

Running

myenv="true" yq eval --null-input '.a = env(myenv)'

will output

a: true

Read numeric environment variable

Running

myenv="12" yq eval --null-input '.a = env(myenv)'

will output

a: 12

Read yaml environment variable

Running

myenv="{b: fish}" yq eval --null-input '.a = env(myenv)'

will output

a: {b: fish}

Read boolean environment variable as a string

Running

myenv="true" yq eval --null-input '.a = strenv(myenv)'

will output

a: "true"

Read numeric environment variable as a string

Running

myenv="12" yq eval --null-input '.a = strenv(myenv)'

will output

a: "12"

Dynamic key lookup with environment variable

Given a sample.yml file of:

cat: meow
dog: woof

then

myenv="cat" yq eval '.[env(myenv)]' sample.yml

will output

meow