Most native TSO commands, including commands that prompt for missing arguments, use TGET for input. This results in a command error, and the command usually terminates.

For commands that are able to read input, the source of the input is first any data that is currently on your stack, and then any data in your REXX program's standard input stream. Regardless of whether the command processes input, all data on the stack is queued to the TSO command. The stack is empty after any TSO command has been run.

The standard input stream can also be queued as input to the TSO command. For example, if you have a file redirected as input and you run a TSO command before processing that file, some or all of the file can be queued to the TSO command. If input is the terminal, queued input can be queued to the TSO command. This characteristic can be used to interact with some TSO commands.

You can disable command input by using the rexxopt() function with NOTSOIN specified.