DFSORT's IFTHEN is fully described in "z/OS DFSORT Application Programming Guide" which is available from:http://www.ibm.com/support/docview.wss? ... g3T7000080
See the "OUTFIL Control Statements" Chapter and look for IFTHEN.
However, if you're not familiar with DFSORT and DFSORT's ICETOOL, I'd suggest reading through "z/OS DFSORT: Getting Started". It's an excellent tutorial, with lots of examples, that will show you how to use DFSORT, DFSORT's ICETOOL and DFSORT Symbols. You can access it online from the link above.