When the SYSIN DD statement is a DD DUMMY, points to an empty file, or is omitted, IEBCOPY will generate a COPY statement that allows you to run IEBCOPY without supplying a control statement data set for SYSIN.

The generated statement can take several forms, depending on what parameters are specified in the JCL EXEC PARM field.

1. When COMPRESS and REPLACE are not specified, the generated statement is: COPY OUTDD=SYSUT2,INDD=SYSUT1 which will copy without replacing from the data set designated by the SYSUT1 DD statement to the data set designated by the SYSUT2 DD statement.
2. When COMPRESS is not specified but REPLACE is specified, the generated statement is: COPY OUTDD=SYSUT2,INDD=(SYSUT1,R) which will copy with replace from the data set designated by the SYSUT1 DD statement to the data set designated by the SYSUT2 DD statement.
3. When COMPRESS is specified, then the generated statement is: COPY OUTDD=SYSUT2,INDD=SYSUT2 which will compress in place the data set designated by the SYSUT2 DD statement.

When any of the parameters COMPRESS, COPY, COPYMOD, or REPLACE are specified in the JCL EXEC PARM field, then SYSIN is opened and a control statement is automatically generated.