PIPE(2) BSD 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
The pipe() 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.
If the flags argument is 0, the behavior is identical to a call to 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
The pipe() 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
The pipe() 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.
The 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
The pipe() 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.
BSD
May 1, 2013 BSD