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PIPE(2) System Calls Manual PIPE(2)

pipe, pipe2create descriptor pair for interprocess communication

#include <unistd.h>

pipe(int fildes[2]);

#include <fcntl.h>
#include <unistd.h>

pipe2(int fildes[2], int flags);

The () 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 of the pipe, and the second connects to the , 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 . 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 () function is identical to pipe() except that the non-blocking I/O mode on both ends of the pipe is determined by the O_NONBLOCK flag in the flags argument and the close-on-exec flag on both the new file descriptors is determined by the O_CLOEXEC flag in the flags argument.

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.

pipe() and pipe2() will succeed unless:

Too many descriptors are active.
The system file table is full.
The fildes buffer is in an invalid area of the process's address space.

In addition, pipe2() may return the following error:

flags is invalid.

sh(1), fork(2), read(2), socketpair(2), write(2)

The pipe() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”). The pipe2() function is expected to conform to a future revision of that standard.

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.

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.

December 10, 2014 OpenBSD-7.0