       pipe ?fileId_var_r fileId_var_w?
              Create  a pipe.  If fileId_var_r and fileId_var_r are specified,
              then pipe will set the a variable named fileId_var_r to  contain
              the  fileId of the side of the pipe that was opened for reading,
              and fileId_var_w will contain the fileId of the side of the pipe
              that was opened for writing.

              If  the fileId variables are not specified, then a list contain-
              ing the read and write fileIdw is returned as the result of  the
              command.
