Using symbols in nested procedures

The general rules described in Using system symbols and JCL symbols also apply to symbols in nested procedures, along with the following rules:

Within a nested procedure, assign only one substitution text per symbol. You can use the same symbol in other nested procedures and assign it different values.
If you assign or nullify the value for a symbol on an EXEC statement that calls a nested procedure, the substitution text that you specify on the EXEC statement is used in the procedure. The EXEC statement overrides any default value you specify on the PROC statement of the nested procedure.
When the EXEC statement that calls the nested procedure does not assign a substitution text to the symbol, the system uses the default substitution text specified on a PROC statement.
One way to provide an override value for a symbolic in a nested procedure is to design the procedure so that it requires no assignment of default symbolic parameter values. If the PROC statement of the inner procedure contains no default value, the system uses the value specified on the EXEC statement of the outer procedure. For example:
```
   //TESTJCL   PROC
   //STEP1     EXEC  TESTJCL1
   //          PEND
   //TESTJCL1  PROC
   //STEP2     EXEC  PGM=IEFBR14,PARM=&PVAL
   //SYSUDUMP  DD    SYSOUT=A
   //          PEND
   //RUNIT     EXEC  TESTJCL,PVAL=EXEC0
```
If you assign or nullify a substitution text for a symbol on a SET statement, the substitution text that you specify on the SET statement is used in all subsequent statements, procedures, and nested procedures. However, if the calling EXEC statement or the PROC statement of the procedure assigns or nullifies the symbol, it only applies to subsequent statements within that PROC and subsequent nested procedures within that procedure.
If you do not assign or nullify a value for a JCL symbol in a nested procedure, the value used for the JCL symbol in this procedure is obtained from the procedure in which this procedure is nested.
If a JCL symbol is not assigned a substitution text or is not nullified, it is an undefined JCL symbol which might cause errors in the JCL.

Table 1 shows rules 2 through 6 in a summary table, which is the order in which the value for a symbol is resolved.

Table 1. Summary of Rules 2 through 6 for Symbols in Nested Procedures
Value Used	Where the symbol is defined
Value Used	EXEC (Rule 2)	PROC Not EXEC (Rule 3)	SET Not PROC Not EXEC (Rule 4)	Nested Value Not SET Not PROC Not EXEC (Rule 5)	None (Rule 6)
EXEC Value	X
PROC Value		X
SET Value			X
Nested Value				X
Undefined					X