NAME
pipe, pipe2
— create descriptor pair for
interprocess communication
LIBRARY
library “libc”
SYNOPSIS
#include
<unistd.h>
int
pipe(int
fildes[2]);
#include
<unistd.h>
#include <fcntl.h>
int
pipe2(int
fildes[2], int
flags);
DESCRIPTION
Thepipe()
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 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
EPIPEinstead of raisingSIGPIPE.
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 contains an invalid value.
SEE ALSO
STANDARDS
The pipe() function conforms to
IEEE Std 1003.1-1990 (“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.