Code:
$ cat tst2
sos,WINXP,1,2,3,4,5,6,7,,9
sos,WINVISTA,1,2,3,4,5,6,7,,9
sos,MAC,1,2,3,4,5,6,7,,9
sos,LINUX,1,2,3,4,5,6,7,,9
tos,winxp,1,2,3,4,5,6,7,winxp,9
tos,winvista,1,2,3,4,5,6,7,winvista,9
tos,mac,1,2,3,4,5,6,7,mac,9
tos,linux,1,2,3,4,5,6,7,linux,9