PIPE(2)                                                   PIPE(2)

          pipe - create an interprocess channel

          int fildes[2];

          The pipe system call creates an I/O mechanism called a pipe.
          The file descriptors returned can be used in read and write
          operations.  When the pipe is written using the descriptor
          fildes[1] up to 4096 bytes of data are buffered before the
          writing process is suspended.  A read using the descriptor
          fildes[0] will pick up the data.  Writes with a count of
          4096 bytes or less are atomic; no other process can inter-
          sperse data.

          It is assumed that after the pipe has been set up, two (or
          more) cooperating processes (created by subsequent fork
          calls) will pass data through the pipe with read and write

          The Shell has a syntax to set up a linear array of processes
          connected by pipes.

          Read calls on an empty pipe (no buffered data) with only one
          end (all write file descriptors closed) returns an end-of-

          sh(1), read(2), write(2), fork(2)

          The function value zero is returned if the pipe was created;
          -1 if too many files are already open.  A signal is gener-
          ated if a write on a pipe with only one end is attempted.

          Should more than 4096 bytes be necessary in any pipe among a
          loop of processes, deadlock will occur.

          (pipe = 42.)
          sys pipe
          (read file descriptor in r0)
          (write file descriptor in r1)