NAME

     pipe - create an interprocess communication channel


SYNOPSIS

     #include <unistd.h>

     int pipe(int fildes[2])


DESCRIPTION

     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 descrip-
     tor fildes[0] will pick up the data.

     PIPE_MAX equals 7168 under MINIX 3, but note that most  sys-
     tems 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 pipes.

     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 attempted.


RETURN VALUE

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


ERRORS

     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.



SEE ALSO

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


NOTES

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


BUGS

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