In SAS, the reserved keyword _NULL_ specifies a SAS data set that has no observations and no variables. When you specify _NULL_ as the name of an output data set, the output is not written. The _NULL_ data set is often used when you want to execute DATA step code

The SAS language provides syntax that enables you to quickly specify a list of variables. SAS statements that accept variable lists include the KEEP and DROP statements, the ARRAY statement, and the OF operator for comma-separated arguments to some functions. You can also use variable lists on the VAR statements