How to extract 4th field if numerics?

view story

http://www.unix.com – I have a file which contains fields comma separated & with each field surrounded by quotes. The 4th field contains either a serial number, the text ABC, the text XYZ or it's blank. I want to only extract records which have a serial number. Here's some sample data: Code: > cat myfile "ABC123","00CJ","SP16","","SP265","","S248","19/05/2003" "ABC123","00CJ","SP16","00240095028","SP265","","S248","19/05/2003" "ABC1 (HowTos)