JSONPath is a complete implementation of http://goessner.net/articles/JsonPath/. JSONPath can be combined with a script language. In many web samples it's combined with javascript. This framework comes without a script language but can be easily extended with one. See example.
It is based on Gval and can be combined with the modular expression languages based on gval. So for script features like multiply, length, regex or many more take a look at the documentation in the GoDoc.