CECI is also called command level interpreter.
Just type CECI on CICS terminal
You will see the following commands (Source IBM)
STATUS: ENTER ONE OF THE FOLLOWING ABend DISAble ISsue RELease SUspend ACquire DISCard Journal RESEtbr SYncpoint ADdress DUmp LInk RESYnc Trace ALlocate ENAble LOad RETRieve Unlock ASKtime ENDbr Monitor RETUrn Verify ASSign ENQ PErform REWrite WAIT BIf ENTer POInt ROute WAITCics BUild EXtract POP SENd WRITE CAncel FEpi POSt SET WRITEQ CHange FOrmattime PURge SIGNOFf Xctl COLlect FREE PUSh SIGNON CONNect FREEMain Query SPOOLClose CONVerse GDs READ SPOOLOpen DELAy GEtmain READNext SPOOLRead DELETE Handle READPrev SPOOLWrite DELETEQ IGnore READQ START DEQ INquire RECeive STARTBr PF 1 HELP 2 HEX 3 END 4 EIB 5 VAR 6 USER 9 MSG
So CECI we can use to get complete syntax of CICS commands. No need to remember commands. Second usage is we can process the commands.
For ex: CECI RETRIVE >>It display complete syntax of the command.
STATUS: ABOUT TO EXECUTE COMMAND NAME=
EXEC CICS RETRieve
< Set() | Into() >
< Length() >
< RTRansid() >
< RTErmid() >
< Queue() >
< Wait >
CECS- we call it as command level syntax checking.
By typing CECS you will get similar screen as in the case CECI. Only difference is that we can not process the commands.