Like the `jq` equivalents, variables are sometimes required for the more complex expressions (or swapping values between fields). Note that there is also an additional `ref` operator that holds a reference (instead of a copy) of the path, allowing you to make multiple changes to the same path. ## Single value variable Given a sample.yml file of: ```yaml a: cat ``` then ```bash yq eval '.a as $foo | $foo' sample.yml ``` will output ```yaml cat ``` ## Multi value variable Given a sample.yml file of: ```yaml - cat - dog ``` then ```bash yq eval '.[] as $foo | $foo' sample.yml ``` will output ```yaml cat dog ``` ## Using variables as a lookup Example taken from [jq](https://stedolan.github.io/jq/manual/#Variable/SymbolicBindingOperator:...as$identifier|...) Given a sample.yml file of: ```yaml "posts": - "title": Frist psot "author": anon - "title": A well-written article "author": person1 "realnames": "anon": Anonymous Coward "person1": Person McPherson ``` then ```bash yq eval '.realnames as $names | .posts[] | {"title":.title, "author": $names[.author]}' sample.yml ``` will output ```yaml title: Frist psot author: Anonymous Coward title: A well-written article author: Person McPherson ``` ## Using variables to swap values Given a sample.yml file of: ```yaml a: a_value b: b_value ``` then ```bash yq eval '.a as $x | .b as $y | .b = $x | .a = $y' sample.yml ``` will output ```yaml a: b_value b: a_value ``` ## Use ref to reference a path repeatedly Note: You may find the `with` operator more useful. Given a sample.yml file of: ```yaml a: b: thing c: something ``` then ```bash yq eval '.a.b ref $x | $x = "new" | $x style="double"' sample.yml ``` will output ```yaml a: b: "new" c: something ```