NAME
pipe, pipe2
— create descriptor pair for
interprocess communication
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
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, close-on-exec flag, and close-on-fork flag of both
new file descriptors are determined by the
O_NONBLOCK, O_CLOEXEC, and
O_CLOFORK flags in the flags
argument, respectively.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ERRORS
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.
SEE ALSO
STANDARDS
The pipe() and
pipe2() functions conform to IEEE
Std 1003.1-2024 (“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
distinct file descriptors. The pipe2() function
appeared in OpenBSD 5.7.