PIPE(2) BSD System Calls Manual PIPE(2)NAMEpipe — create descriptor pair for interprocess communication
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <unistd.h>
int
pipe(int fildes[2]);
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.
pipe2() will also fail if:
[EINVAL] flags is other than O_NONBLOCK or O_CLOEXEC.
SEE ALSOsh(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 6 AT&T UNIX. The pipe2()
function is inspired from Linux and appeared in NetBSD 6.0.
BSD January 23, 2012 BSD
