evaluateELString
Description: This function evaluates the Expression Language inside the variable value.
Subject Type: String
Arguments: No arguments
Return Type: String
Examples: If one of the registry variable named "query" has value "SELECT * FROM TABLE WHERE ID = ${id}" and the value of the "id" field, we are getting from the flowfile attributes (i.e. id=20) then the Expression ${query:evaluateELString()}
will return SELECT * FROM TABLE WHERE ID = 20