IEBCOPY user exit routines enable a program to supply IEBCOPY control statements instead of IEBCOPY reading control statements from SYSIN. (Note: you cannot specify these user exit routines when you invoke IEBCOPY via JCL.) This makes it possible, for instance, to control the command input stream by providing an exit routine for SYSIN. Also, the user exit can pass information back to IEBCOPY to be added to the SYSPRINT output stream.

When IEBCOPY calls a user exit, standard linkage must be used and standard register convention must be followed; that is, register 1 points to the argument list and it might be above the 16 MB line, register 13 points to a standard 72-byte save area that resides above the line, register 14 contains the return address, and register 15 contains the entry point address. On exit from the user exit routine, CPLST_PARMLIST_RC contains the exit routine's return code. The list of return codes that are expected from the IEBCOPY user exits is contained in the IEBCPLST mapping macro.