Look at this JCL -
//F EXEC PGM=UCHECK
//STEPLIB DD DISP=SHR,DSN=XXXXXX.UCHECK.LOAD
//SYSPRINT DD DISP=(,CATLG),UNIT=SYSDA,SPACE=(TRK,(1,1)),
// DSN=XXXXXX.UCHECK.SYSPRINT(+1)
//LU DD DISP=SHR,DSN=XXXXXX.SCANLU.INPUT
//DB DD DISP=OLD,DSN=XXXXXX.UCHECK.DB
//FLIST EXEC PGM=IEBGENER
//SYSPRINT DD DUMMY
//SYSIN DD DUMMY
//SYSUT1 DD DISP=OLD,DSN=XXXXXX.UCHECK.SYSPRINT(+1)
//SYSUT2 DD SYSOUT=*,DCB=(RECFM=VA,LRECL=125,BLKSIZE=129)
Step F creates new generation in the GDG base XXXXXX.UCHECK.SYSPRINT, step FLIST "prints" prints the data set. Here is an extract from from the JESYSMSG data set -
IEF236I ALLOC. FOR XXXXXXU F
IGD103I SMS ALLOCATED TO DDNAME STEPLIB
IGD101I SMS ALLOCATED TO DDNAME (SYSPRINT)
DSN (XXXXXX.UCHECK.SYSPRINT.G0603V00 )
STORCLAS (USER) MGMTCLAS ( ) DATACLAS ( )
VOL SER NOS= VVVV34
IGD103I SMS ALLOCATED TO DDNAME LU
IGD103I SMS ALLOCATED TO DDNAME DB
IEF142I XXXXXXU F - STEP WAS EXECUTED - COND CODE 0000
IGD104I XXXXXX.UCHECK.LOAD RETAINED, DDNAME=STEPLIB
IGD107I XXXXXX.UCHECK.SYSPRINT.G0603V00 ROLLED IN, DDNAME=SYSPRINT
IGD104I XXXXXX.SCANLU.INPUT RETAINED, DDNAME=LU
IGD104I XXXXXX.UCHECK.DB RETAINED, DDNAME=DB
IEF373I STEP/F /START 2016363.1055
IEF374I STEP/F /STOP 2016363.1055 CPU 0MIN 00.21SEC SRB 0MIN 00.00S
IEF236I ALLOC. FOR XXXXXXU FLIST
IEF237I DMY ALLOCATED TO SYSPRINT
IEF237I DMY ALLOCATED TO SYSIN
IGD103I SMS ALLOCATED TO DDNAME SYSUT1
IEF237I JES2 ALLOCATED TO SYSUT2
IEF142I XXXXXXU FLIST - STEP WAS EXECUTED - COND CODE 0000
IGD104I XXXXXX.UCHECK.SYSPRINT.G0603V00 RETAINED, DDNAME=SYSUT1
IEF285I XXXXXX.XXXXXXU.JOB99472.D0000105.? SYSOUT
IEF373I STEP/FLIST /START 2016363.1055
IEF374I STEP/FLIST /STOP 2016363.1055 CPU 0MIN 00.04SEC SRB 0MIN 00.00S
The IGD101I message tells us it created a new data set XXXXXX.UCHECK.SYSPRINT.G0603V00 for the generation data group. It does not also say it also deleted G0683V00 because the GDG is full at 20 data sets.
The IGD107I message is telling us, basically, that the catalog has actually been updated.