S9 EXT  (sys:make-input-port integer)   ==>  input-port
        (sys:make-output-port integer)  ==>  output-port

Create a new input or output port and assign it to the Unix file
descriptor specified in the INTEGER argument. The file descriptor
must be open and match the type of the port to be created, i.e.
a file descriptor passed to SYS:MAKE-INPUT-PORT must be open for
reading and a descriptor passed to SYS:MAKE-OUTPUT-PORT must be
open for writing.

(sys:make-input-port 0)   ==>  #<input port>
(sys:make-output-port 2)  ==>  #<output port>
