Field extraction of log file which each line has different format, how can I include all format in one regex

I am doing field extraction for a log file format as below line 1: field1, field2, field3, field4 line 2: field1, field2, field3, field5, field4 line 3: field1, field2, field3, field4 I can write separate regex1 for line 1 and regex 2 for line 2 format, but when I do field extraction, I can only use one regex, how can I put both regex in to cover all log format? Any suggestions? Cheers Sam