yday's data &today's data

Hi all,
following is my cl program.MURALI0 is previous day's
file.MURALI1 is today's file.
prior to generating today's file(MURALI1) i shall be
taking yesterday's file into MURALI0 as per first copy
file command in my program.The program is running
fine.But I have problem if i run this program more
than once in the same day since it replacing MURALI0.
is there any command (please suggest me) i can include
before the first copy file command to compare the
dates (OR)
If I execute the program more than once  ,file MURALI0
is having the same data as MURALI1.
How do i make changes to my program sothat it can be
run any number of times that day  without changing the
data in the MURALI0(after 1st run).
for my first time execution of the program,file
MURALI0 will contain yesterday's data,
for second execution of the program ,file MURALI0 will
get today's data since it is copying from MURALI1.so
teh very purpose of the program is nt working.
I want to see the program work for any number of runs
without loosing yesterday's data in MURALI0.
please suggest me i shall be greatful to you,
Thanks,
Murali.




===========

PGM                                                   
            
     /*THIS IS FOR YDAY'S DATA MURALI0 CONSISTS
PREVIOUS DAY */    
             CPYF       FROMFILE(YMNTEST/MURALI1) +   
            
                          TOFILE(YMNTEST/MURALI0)
MBROPT(*REPLACE) CRTFILE(*YES) FROMRCD(1)             
   
                                
             YCTAC200C  REQSFILE(YDJ.REQS)
POSFILE(YDJPOSF1) OUTFILE(YDJAC200)                   
    
     /* COPY FILE YDJAC200 TO MURALI1 */           
              RUNQRY     QRY(YMNTEST/YIMQRY) 

              /*combines MURALI0 &MURALI1 and
generates required output */              
              RUNQRY     QRY(YMNTEST/YIMQRY01)        
                  
                                                      
 
                                                      
                                                      
       
                                                      
                  
 ENDPGM                                               
                  
==============

__________________________________
Do you Yahoo!?
Protect your identity with Yahoo! Mail AddressGuard
http://antispam.yahoo.com/whatsnewfree