PIPE(II)                      8/5/73                     PIPE(II)

     pipe - create an interprocess channel

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

     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
     returned in r1 (resp. fildes[1]), up to 4096 bytes  of  data
     are  buffered  before  the  writing process is suspended.  A
     read using the descriptor returned in r0  (resp.  fildes[0])
     will pick up the 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)  return  an  end-of-
     file.  Write calls under similar conditions generate a fatal
     signal (signal(II)); if the signal is ignored, an error  is
     returned on the write.

     sh(I), read(II), write(II), fork(II)

     The  error  bit (c-bit) is set if too many files are already
     open.  From C, a -1 returned value indicates  an  error.   A
     signal  is  generated if a write on a pipe with only one end
     is attempted.


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