[<lookup_name>]: The name of the lookup.
external_cmd = <string>: The command and arguments that the Splunk platform should invoke to perform the lookup. The Splunk platform expects the command to be the name of the script, such as external_lookup.py.
external_type = [python|executable|kvstore|geo]: The type of script being used for the lookup. Can be python, for a Python script, or executable, for a binary executable. The kvstore and geo values are reserved for KV store lookups and geospatial lookups, respectively.
fields_list = <string>: is a list of all fields that are supported by the external lookup. The fields must be delimited by a comma followed by a space.
See fields_list above. I don't want to limit this lookup to any fields right now (this will not be an automatic lookup). Can I simply not add that line so that the external lookup command will work on any field I send to it?