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5.13.5 Other Parts of the I/O System
This section lists some of the other parts of REXX and the
environments around REXX that may be considered a part of the I/O

     The stack be used to communicate with external environments.
     At the REXX side, the interface to the stack is the
     instructions PUSH, PULL, PARSE PULL, and QUEUE; and the built-
     in function QUEUED().  These can be used to communicate with
     external programs by storing data to be transferred on the

[The STREAM() built-in function.]
     This function is used to control various aspects about the
     files manipulated with the other standard I/O functions. The
     standard says very little about this function, and leaves it
     up to the implementor to specify the rest. Operations like
     opening, closing, truncating, and changing modes

[The SAY instruction.]
     The SAY instruction can be used to write data to the default
     output stream. If you use redirection, you can indirectly use
     it to write data to a file.

[The ADDRESS instruction.]
     The ADDRESS instruction and commands can be used to operate
     on files, depending on the power of your host environments
     and operating system.

[The VALUE() built-in function.]
     The function VALUE(), when used with three parameters, can be
     used to communicate with external host environments and the
     operating system. However, this depends on the implementation
     of your interpreter.

     The SAA API provides several operations that can be used to
     communicate between processes. In general, SAA API allows you
     to perform the operations listed above from a binary program
     written in a language other than REXX.

And of course, I/O is performed whenever a REXX program or
external function is started.