@Override
        public String getName() {
            return "envVar";
        }
@param var         The value being piped into the filter
@param interpreter
@param args        The filter args. One argument, the name of the env var to use for
                   substitution.
@return The value as a bash style variable substitution
stroom-app/src/test/java/stroom/dist/GenerateDistributionConfig.java