yq/pkg/yqlib/doc/operators/headers/eval.md

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, beit a path .a.b.c | select(. == "cat"), or an update .a.b.c = "gogo".

Tip: This can be useful way parameterize complex scripts.