This re2 (using Go in my case) matches the APRS-IS header.
The format of the APRS-IS packet is TNC2 standard:
SOURCE>DESTINATION,PATH:PACKET
This regex matches the Q construct format used by APRS-IS:
`SOURCE>DESTINATION,PATH,QCON,FROMCALL:
The result is a series of capturable groups:
Group 1: Src SSID
Group 2: Dest SSID
Group 3: Path
Group 4: Q construct
Group 5: From Calll