There are two program forms where you can use User Exits: a User Function program or a GRIP program. The procedure for using exits is similar for both. One of the major differences is the use of the asterisk (*) in the environment variable definition. The asterisk specifies that the variable points to a GRIP program.
User Exits for GRIP only
Write a GRIP program that performs the task you desire.
Define the pointer to the GRIP program. The file pointer is a file specification to your GRIP program.
Describe's how to define these file pointers: links or environment variables for different operating systems.
The following GPAs also perform user exits functions:
&UENUM
&UEXERR
&UESTR