Using the explicit form of the EXEC command involves naming the data set that contains the REXX exec or CLIST. You can create the fully-qualified data set name and determine whether it will run as a REXX exec or a CLIST. You can specify either the CLIST or EXEC operand to denote that the data set be run as a REXX exec or CLIST. If you specify neither operand, the data set is run based on the following specifications or defaults:

If you know that the procedure being run is a CLIST, you can code the CLIST operand. If you know that the procedure being run is a REXX exec, you can code the EXEC operand. If you do not code the CLIST or EXEC operand on the EXEC command, the EXEC command processor examines line 1 of the procedure for the characters "REXX" within a comment. (The characters "REXX" can be in uppercase, lowercase, or mixed-case.) This is known as the REXX exec identifier. If the EXEC command finds the REXX exec identifier, the EXEC command runs the procedure as a REXX exec. Otherwise, it runs the procedure as a CLIST.

In addition to determining if a procedure is run as a REXX exec or a CLIST, the CLIST and EXEC operands of the EXEC command determine how to name a non-fully-qualified data set. If you specify EXEC, a non-fully-qualified data set name is suffixed with the "exec" qualifier. If you specify CLIST, or if you omit either EXEC or CLIST, a non-fully-qualified name is suffixed with the qualifier "clist".

The following examples use the explicit form of the EXEC command and show how the procedure runs in each case.