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pipe(2) [freebsd man page]

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

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) 							   System Calls 							   pipe(2)

pipe - create an interprocess channel SYNOPSIS
#include <unistd.h> int pipe(int fildes[2]); DESCRIPTION
The pipe() function creates an I/O mechanism called a pipe and returns two file descriptors, fildes[0] and fildes[1]. The files associated with fildes[0] and fildes[1] are streams and are both opened for reading and writing. The O_NDELAY, O_NONBLOCK, and FD_CLOEXEC flags are cleared on both file descriptors. The fcntl(2) function can be used to set these flags. A read from fildes[0] accesses the data written to fildes[1] on a first-in-first-out (FIFO) basis and a read from fildes[1] accesses the data written to fildes[0] also on a FIFO basis. Upon successful completion pipe() marks for update the st_atime, st_ctime, and st_mtime fields of the pipe. RETURN VALUES
Upon successful completion, 0 is returned. Otherwise, -1 is returned and errno is set to indicate the error. ERRORS
The pipe() function will fail if: EMFILE More than {OPEN_MAX} file descriptors are already in use by this process. ENFILE The number of simultaneously open files in the system would exceed a system-imposed limit. ATTRIBUTES
See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |Async-Signal-Safe | +-----------------------------+-----------------------------+ SEE ALSO
sh(1), fcntl(2), fstat(2), getmsg(2), poll(2), putmsg(2), read(2), write(2), attributes(5), standards(5), streamio(7I) NOTES
Since a pipe is bi-directional, there are two separate flows of data. Therefore, the size (st_size) returned by a call to fstat(2) with argument fildes[0] or fildes[1] is the number of bytes available for reading from fildes[0] or fildes[1] respectively. Previously, the size (st_size) returned by a call to fstat() with argument fildes[1] (the write-end) was the number of bytes available for reading from fildes[0] (the read-end). SunOS 5.11 23 Apr 2002 pipe(2)
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