pipe(2) - NetBSD Manual Pages

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PIPE(2)                   NetBSD System Calls Manual                   PIPE(2)


NAME

     pipe, pipe2 -- create descriptor pair for interprocess communication


LIBRARY

     Standard C Library (libc, -lc)


SYNOPSIS

     #include <unistd.h>

     int
     pipe(int fildes[2]);

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

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


DESCRIPTION

     The pipe() function creates a pipe, which is an object allowing unidirec-
     tional 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 behaves exactly like pipe() only it allows extra
     flags to be set on the returned file descriptor.  The following flags are
     valid:

           O_CLOEXEC   Set the ``close-on-exec'' property.

           O_NONBLOCK  Sets non-blocking I/O.

           O_NOSIGPIPE
                       Return EPIPE instead of raising SIGPIPE.


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() and pipe2() calls will fail if:

     [EFAULT]           The fildes buffer is in an invalid area of the
                        process's address space.  The reliable detection of
                        this error cannot be guaranteed; when not detected, a
                        signal may be delivered to the process, indicating an
                        address violation.

     [EMFILE]           Too many descriptors are active.

     [ENFILE]           The system file table is full.

     [ENOMEM]           Not enough kernel memory to establish a pipe.

     pipe2() will also fail if:

     [EINVAL]           flags contains an invalid value.


SEE ALSO

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


STANDARDS

     The pipe() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1'').


HISTORY

     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 is inspired from Linux and appeared in NetBSD 6.0.

NetBSD 10.1                    November 27, 2020                   NetBSD 10.1