PIPE(2)                       System Calls Manual                      PIPE(2)


     pipe, pipe2 - create descriptor pair for interprocess communication


     #include <unistd.h>

     pipe(int fildes[2]);

     #include <fcntl.h>
     #include <unistd.h>

     pipe2(int fildes[2], int flags);


     The pipe() function creates a pipe, which is an object allowing
     unidirectional data flow, and allocates a pair of file descriptors.  The
     first descriptor connects to the read end of the pipe, and the second
     connects to the write end, so that data written to fildes[1] appears on
     (i.e., can be read from) fildes[0].  This allows the output of one
     program to be sent to another program: the source's standard output is
     set up to be the write end of the pipe, and the sink's standard input is
     set up to be the read end of the pipe.  The pipe itself persists until
     all its associated descriptors are closed.

     A pipe whose read or write end has been closed is considered widowed.
     Writing on such a pipe causes the writing process to receive a SIGPIPE
     signal.  Widowing a pipe is the only way to deliver end-of-file to a
     reader: after the reader consumes any buffered data, reading a widowed
     pipe returns a zero count.

     The pipe2() function is identical to pipe() except that the non-blocking
     I/O mode on both ends of the pipe is determined by the O_NONBLOCK flag in
     the flags argument and the close-on-exec flag on both the new file
     descriptors is determined by the O_CLOEXEC flag in the flags argument.


     Upon successful completion, the value 0 is returned; otherwise the
     value -1 is returned and the global variable errno is set to indicate the


     pipe() and pipe2() will succeed unless:

     [EMFILE]           Too many descriptors are active.

     [ENFILE]           The system file table is full.

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

     In addition, pipe2() may return the following error:

     [EINVAL]           flags is invalid.


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


     The pipe() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').  The
     pipe2() function is expected to conform to a future revision of that

     As an extension, the pipe provided is actually capable of moving data
     bidirectionally.  This is compatible with SVR4.  However, this is non-
     POSIX behaviour which should not be relied on, for reasons of


     A pipe() function call appeared in Version 3 AT&T UNIX.  Since Version 4
     AT&T UNIX, it allocates two distinct file descriptors.  The pipe2()
     function appeared in OpenBSD 5.7.

OpenBSD 5.7                    December 10, 2014                   OpenBSD 5.7

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