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pipe(2) [netbsd man page]

PIPE(2) 						      BSD System Calls Manual							   PIPE(2)

NAME
pipe -- 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() 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 behaves exactly like pipe() only it allows extra flags to be set on the returned file descriptor. The following flags are valid: O_CLOEXEC Set the ``close-on-exec'' property. O_NONBLOCK Sets non-blocking I/O. O_NOSIGPIPE Return EPIPE instead of raising SIGPIPE. RETURN VALUES
On successful creation of the pipe, zero is returned. Otherwise, a value of -1 is returned and the variable errno set to indicate the error. ERRORS
The pipe() and pipe2() calls will fail if: [EFAULT] The fildes buffer is in an invalid area of the process's address space. The reliable detection of this error cannot be guaranteed; when not detected, a signal may be delivered to the process, indicating an address violation. [EMFILE] Too many descriptors are active. [ENFILE] The system file table is full. pipe2() will also fail if: [EINVAL] flags is other than O_NONBLOCK or O_CLOEXEC. SEE ALSO
sh(1), fork(2), read(2), socketpair(2), write(2) STANDARDS
The pipe() function conforms to ISO/IEC 9945-1:1990 (``POSIX.1''). HISTORY
A pipe() function call appeared in Version 6 AT&T UNIX. The pipe2() function is inspired from Linux and appeared in NetBSD 6.0. BSD
January 23, 2012 BSD

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pipe(2) 							System Calls Manual							   pipe(2)

Name
       pipe - create an interprocess channel

Syntax
       include <limits.h> /*Definition of PIPE_MAX*/
       pipe(fildes)
       int fildes[2];

Arguments
       fildes	 Passing an address as an array of two integers into the system call.

Description
       The system call creates an I/O mechanism called a pipe.	The file descriptors returned can be used in and operations.  Their integer values
       will be the two lowest available at the time of the function call.  The O_NONBLOCK and FD_CLOEXEC flags will be clear on both file descrip-
       tors.

       When the pipe is written using the descriptor fildes[1], up to PIPE_MAX bytes of data are buffered before the writing process is suspended.
       A read using the descriptor fildes[0] picks up the data.

       It is assumed that after the pipe has been set up, two (or more) cooperating processes (created by subsequent calls) pass data through  the
       pipe with and calls.

       The shell has a syntax to set up a linear array of processes connected by pipes.

       For further information on how and calls behave with pipes, see the and reference pages.

       A signal is generated if a write on a pipe with only one end is attempted.

Restrictions
       Should more than 4096 bytes be necessary in any pipe among a loop of processes, deadlock may occur.

       The  underlying	implementation	of  pipes is no longer socket based, but rather implemented through the file system.  Any application that
       needs socket functionality from pipes should use the system call.

Return Values
       The function value zero is returned if the pipe was created; -1 if an error occurred.

Diagnostics
       The call fails if:

       [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.

Environment
       Differs from the System V definition in that ENFILE is not a possible error condition.

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

																	   pipe(2)

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