The language processor evaluates each expression in a REXX program. This evaluation results in a character string (which may be the null string). The character string is prepared appropriately and submitted to the host command environment. The environment processes the string as a command, and, after processing is complete, returns control to the language processor. If the string is not a valid command for the current host command environment, a failure occurs and the special variable RC contains the return code from the host command environment.