Query a File on MacOS to extract and set a Session Variable (APM)

I would like to know if there is a way to query a specific file on MacOS to extract a "GUID" from said file and set it as a session variable?

 

My investigations so far have led me down the "Variable Assign" route, but I am not sure if this is the right path?

 

Any assistance would be greatly appreciated.

 

Thanks