pipe - create an interprocess communication channel

     #include <unistd.h>

     int pipe(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  PIPE_MAX  bytes  of
     data  are buffered before the writing process is suspended.  A read using
     the descriptor fildes[0] will pick up the data.

     PIPE_MAX equals 7168 under Minix, but note that most systems use 4096.

     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 calls.

     The shell has a syntax to set up a linear array of processes connected by

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

     The signal SIGPIPE is generated if a write on a pipe with only one end is

     The function value zero is returned if the pipe was  created;  -1  if  an
     error occurred.

     The pipe call will fail if:

     [EMFILE]       Too many descriptors are active.

     [ENFILE]       The system file table is full.

     [ENOSPC]       The pipe file system (usually the root file system) has no
                    free inodes.

     [EFAULT]       The fildes buffer is in an invalid area of  the  process's
                    address space.

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

     Writes may return ENOSPC errors if no pipe data can be buffered,  because
     the pipe file system is full.

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