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PIPE(2) | 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]);
int
pipe2
(int
fildes[2], int
flags);
DESCRIPTION¶
Thepipe
() system call creates a
pipe, which is an object allowing bidirectional
data flow, and allocates a pair of file descriptors.
The pipe2
() system call allows control over
the attributes of the file descriptors via the
flags argument. Values for
flags are constructed by a bitwise-inclusive
OR of flags from the following list, defined in
<fcntl.h>
:
O_CLOEXEC
- Set the close-on-exec flag for the new file descriptors.
O_NONBLOCK
- Set the non-blocking flag for the ends of the pipe.
pipe
().
By convention, the first descriptor is normally used as the
read end of the pipe, and the second is normally
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 that has had an end 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 bidirectional nature of this implementation of pipes is not portable to
older systems, so it is recommended to use the convention for using the
endpoints in the traditional manner when using a pipe in one direction.
RETURN VALUES¶
Thepipe
() function returns the
value 0 if successful; otherwise the value -1 is returned and
the global variable errno is set to indicate
the error.
ERRORS¶
Thepipe
() and
pipe2
() system calls will fail if:
- [
EMFILE
] - Too many descriptors are active.
- [
ENFILE
] - The system file table is full.
- [
ENOMEM
] - Not enough kernel memory to establish a pipe.
pipe2
() system call will also fail if:
- [
EINVAL
] - The flags argument is invalid.
SEE ALSO¶
sh(1), fork(2), read(2), socketpair(2), write(2)HISTORY¶
Thepipe
() function appeared in
Version 3 AT&T UNIX.
Bidirectional pipes were first used on AT&T System V
Release 4 UNIX.
The pipe2
() function appeared in
FreeBSD 10.0.May 1, 2013 | Debian |