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pipe(2) [freebsd man page]

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

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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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