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


     pipe - create a pipe


     (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 are ignored.


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


     The error bit (c-bit) is  set  if  more  than  8  files  are

     already  open.   From  C,  a  -1 returned value indicates an