Splitting serial port into two virtual ports

[Craig Young]

My weather station outputs a single serial port data stream.  On a Pi I have a python program which opens the port and sends the weather data to WeatherUnderground.  The next step is to bring up Weewx and connect to the incoming datastream and output to Weatherunderground.  But, during the testing phase I do not want to interrupt the feed to WU.

Has anyone on the forum here split an incoming physical serial stream into two output virtual streams?  I could then leave one virtual stream as the WU updates and use the second stream as the input to the Weewx test system.  Once the Weewx installation is working successfully I can then revert it to use the direct feed from the station.

I have seen a few solutions while scanning the internet but thought I would check here first and see what has been successfully used.

Craig