Eval

Use eval to dynamically process an expression - for instance from an environment variable.

eval takes a single argument, and evaluates that as a yq expression. Any valid expression can be used, be it a path .a.b.c | select(. == "cat"), or an update .a.b.c = "gogo".

Tip: This can be a useful way to parameterise complex scripts.

Dynamically evaluate a path

Given a sample.yml file of:

{pathExp: '.a.b[] | select(.name == "cat")', a: {b: [{name: dog}, {name: cat}]}}

then

yq 'eval(.pathExp)' sample.yml

will output

{name: cat}

Dynamically update a path from an environment variable

The env variable can be any valid yq expression.