The system under which REXX programs run is assumed to include at least one environment for processing commands. An environment is selected by default on entry to a REXX program. You can change the environment by using the ADDRESS instruction. You can find out the name of the current environment by using the ADDRESS built-in function. The underlying operating system defines environments external to the REXX program. The default environment for a REXX/CICS program is REXXCICS.