Null or unspecified values ($NULL)

For some selection criteria and Enhanced Allocation Management function keywords, the reserved string ($NULL) designates that a null or unspecified value exists for the particular item.

For example, in the following DD statement, a selection criterion of ADISP=$NULL is considered to be a match because the abnormal disposition was not specified using the JCL DD DISP keyword:

//DD1 DD DSNAME=PAY.FILE,DISP=(,CATLG)

Note: For selection criteria keywords, use only the EQ and NE comparison operands with $NULL. Other comparison operands are ignored.

For selection criteria processing, $NULL indicates that an allocation attribute was not specified for a JCL, DYNALLOC, or DEFINE statement. Specifying $NULL allows you to set a value if no value was specified. For example:

INCLUDE 
     DEVICECLASS=TAPE
     RETPD=$NULL
     SET_RETPD=1

In the example, when an allocation is directed to tape, if no retention period is specified, then set it to one day.