If you write a REXX program to run in TSO/E, it is likely that you will have to alter the REXX program to run it in a z/OS shell environment. Some of the differences between the two environments that you need to consider are:

• You can use the spawn syscall command to run z/OS shell commands from the TSO/E environment.
• Using the syscalls('ON') function at the beginning of the REXX program is required in TSO/E, but not in a z/OS shell environment. If you use syscalls('ON') in a z/OS shell environment, it clears the __argv. and __environment. stems. For this reason, it is not recommended that you use syscalls('ON') in a z/OS shell environment. Using syscalls('ON') in a z/OS shell environment also sets up the REXX predefined variables and blocks all signals. On entry to a REXX program in a z/OS shell environment, the REXX predefined variables are already set.
• In TSO/E, the syscalls('OFF') function ends the process, but the REXX program continues to run. In the z/OS shells, the syscalls('OFF') function undubs the task and the REXX program continues.
• PARSE SOURCE returns different tokens in TSO/E and in a z/OS shell environment. A REXX program uses the tokens to determine how it was run.
• In TSO/E, the variables __argv.0 and __environment.0 are set to zero (0).