/sys$common/syshlp/helplib.hlb CC, Run-time functions, pipe  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Creates a temporary mailbox.  You must use a mailbox to read and
  write data between the parent and child.  The channels through
  which the processes communicate are called a pipe.

  Syntax:

       #include <unistd.h>

       int pipe(int file_descriptor[2]); (POSIX-1)

       int pipe(int file_descriptor[2],...); (Compaq C Extension)

  where:

  file_descriptor[2] - is an array of file descriptors.  A pipe is
  implemented as an array of file descriptors associated with a
  mailbox.  These mailbox descriptors are special in that these are
  the only file descriptors which, when passed to the isapipe
  function, will return 1.  Element 0 of the file_descriptor array
  contains the descriptor for reading; element 1 contains the
  descriptor for writing.

  ..  represents two optional arguments:

  flags - If either the O_NDELAY or O_NONBLOCK bit is set, the I/O
  operations to the mailbox through the specified file descriptors
  will terminate immediately, rather than waiting for another
  process.

  If, for example, the O_NDELAY bit is set and the child issues a
  read request to the mailbox before the parent has put any data into
  it, the read terminates immediately with zero status.  If neither
  the O_NDELAY nor O_NONBLOCK bit is set, the child will be waiting
  on the read until the parent writes any data into the mailbox.
  This is the default behavior if no flag argument is specified.

  The values of O_NDELAY and O_NONBLOCK are defined in the <fcntl.h>
  header file.  Any other bits in the flag argument are ignored.  You
  must specify this argument if the second optional, positional
  argument bufsize is specified.  If the flag argument is needed only
  to allow specification of the bufsize argument, specify flag as
  zero.

  bufsize -- specifies the size of the mailbox, in bytes.  If you do
  not specify this argument, a mailbox is created with a default size
  of 512 bytes.