PIPE(2)PIPE(2)NAME
pipe - create an interprocess channel
SYNOPSIS
#include <unistd.h>
int pipe(int fildes[2]);
int pipe2(int fildes[2], int flags);
DESCRIPTION
The pipe() and pipe2() functions create an I/O mechanism called a pipe
and returns two file descriptors, fildes[0] and fildes[1]. The files
associated with fildes[0] and fildes[1] are streams and are both opened
for reading and writing. The pipe() call will clear the O_NDELAY,
O_NONBLOCK, and FD_CLOEXEC flags on both file descriptors. The fcntl(2)
function can be used to set these flags.
The pipe2() call will clear the O_NDELAY on both filedescriptors. The
flags argument may be used to specify attributes on both file descrip‐
tors. pipe2() called with a flags value of 0 will behave identically
to pipe(). Values for flags are constructed by a bitwise-inclusive-OR
of flags from the following list, defined in <fcntl.h>.
O_NONBLOCK
Both file descriptors will be placed in non-blocking mode. This
corresponds to the O_NONBLOCK flag to fcntl(2).
O_CLOEXEC
Both file descriptors will be opened with the FD_CLOEXEC flag set.
Both file descriptors will be closed prior to any future exec()
calls.
A read from fildes[0] accesses the data written to fildes[1] on a first-in-
first-out (FIFO) basis and a read from fildes[1] accesses the data written to
fildes[0] also on a FIFO basis.
Upon successful completion pipe() marks for update the st_atime, st_ctime, and
st_mtime fields of the pipe.RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, −1 is returned
and errno is set to indicate the error.
ERRORS
The pipe() and pipe2() functions will fail if:
EMFILE
More than {OPEN_MAX} file descriptors are already in use by
this process.
ENFILE
The number of simultaneously open files in the system would
exceed a system-imposed limit.
EFAULT
The fildes[2] argument points to an illegal address.
The pipe2() function will also fail if:
EINVAL
The flags argument is illegal. Valid flags are zero or a bit‐
wise inclusive-OR of O_CLOEXEC and O_NONBLOCK.
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌────────────────────┬───────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼───────────────────┤
│Interface Stability │ Standard │
├────────────────────┼───────────────────┤
│MT-Level │ Async-Signal-Safe │
└────────────────────┴───────────────────┘
SEE ALSOsh(1), fcntl(2), fstat(2), getmsg(2), poll(2), putmsg(2), read(2),
write(2), open(2), attributes(5), standards(5), streamio(7I)NOTES
Since a pipe is bi-directional, there are two separate flows of data.
Therefore, the size (st_size) returned by a call to fstat(2) with argu‐
ment fildes[0] or fildes[1] is the number of bytes available for read‐
ing from fildes[0] or fildes[1] respectively. Previously, the size
(st_size) returned by a call to fstat() with argument fildes[1] (the
write-end) was the number of bytes available for reading from fildes[0]
(the read-end).
Apr 19, 2013 PIPE(2)