pipe



PIPE(2)                   OpenBSD Programmer's Manual                  PIPE(2)


NAME

     pipe - create descriptor pair for interprocess communication


SYNOPSIS

     #include <unistd.h>

     int
     pipe(int fildes[2]);


DESCRIPTION

     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.


RETURN VALUES

     On successful creation of the pipe, zero is returned.  Otherwise, a value
     of -1 is returned and the variable errno set to indicate the error.


ERRORS

     The pipe() call will fail if:

     [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.


SEE ALSO

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


STANDARDS

     The pipe() function conforms to IEEE Std 1003.1-2008 (``POSIX.1'').

     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
     portability.


HISTORY

     A pipe() function call appeared in Version 3 AT&T UNIX.  Since Version 4
     AT&T UNIX, it allocates two distict file descriptors.

OpenBSD 5.4                      July 17, 2013                     OpenBSD 5.4

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