tee — duplicating pipe content
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <fcntl.h>
ssize_t
tee( |
int fd_in, |
| int fd_out, | |
| size_t len, | |
unsigned int flags); |
tee() duplicates up to
len bytes of data
from the pipe referred to by the file descriptor fd_in to the pipe referred to
by the file descriptor fd_out. It does not consume the
data that is duplicated from fd_in; therefore, that data can
be copied by a subsequent splice(2).
flags is a bit
mask that is composed by ORing together zero or more of the
following values:
SPLICE_F_MOVECurrently has no effect for tee(); see splice(2).
SPLICE_F_NONBLOCKDo not block on I/O; see splice(2) for further details.
SPLICE_F_MORECurrently has no effect for tee(), but may be implemented in the
future; see splice(2).
SPLICE_F_GIFTUnused for tee(); see
vmsplice(2).
Upon successful completion, tee() returns the number of bytes that were
duplicated between the input and output. A return value of 0
means that there was no data to transfer, and it would not
make sense to block, because there are no writers connected
to the write end of the pipe referred to by fd_in.
On error, tee() returns
−1 and errno is set to
indicate the error.
SPLICE_F_NONBLOCK was
specified in flags, and the operation
would block.
fd_in or
fd_out does not
refer to a pipe; or fd_in and fd_out refer to the same
pipe.
Out of memory.
The tee() system call first
appeared in Linux 2.6.17; library support was added to glibc
in version 2.5.
Conceptually, tee() copies
the data between the two pipes. In reality no real data
copying takes place though: under the covers, tee() assigns data to the output by merely
grabbing a reference to the input.
The example below implements a basic tee(1) program using the
tee() system call. Here is an
example of its use:
$ date |./a.out out.log | cat Tue Oct 28 10:06:00 CET 2014 $ cat out.log Tue Oct 28 10:06:00 CET 2014
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <limits.h>
int
main(int argc, char *argv[])
{
int fd;
int len, slen;
if (argc != 2) {
fprintf(stderr, "Usage: %s <file>\n", argv[0]);
exit(EXIT_FAILURE);
}
fd = open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644);
if (fd == −1) {
perror("open");
exit(EXIT_FAILURE);
}
do {
/*
* tee stdin to stdout.
*/
len = tee(STDIN_FILENO, STDOUT_FILENO,
INT_MAX, SPLICE_F_NONBLOCK);
if (len < 0) {
if (errno == EAGAIN)
continue;
perror("tee");
exit(EXIT_FAILURE);
} else
if (len == 0)
break;
/*
* Consume stdin by splicing it to a file.
*/
while (len > 0) {
slen = splice(STDIN_FILENO, NULL, fd, NULL,
len, SPLICE_F_MOVE);
if (slen < 0) {
perror("splice");
break;
}
len −= slen;
}
} while (1);
close(fd);
exit(EXIT_SUCCESS);
}
This page is part of release 4.07 of the Linux man-pages project. A
description of the project, information about reporting bugs,
and the latest version of this page, can be found at
https://www.kernel.org/doc/man−pages/.
|
This manpage is Copyright (C) 2006 Jens Axboe and Copyright (C) 2006 Michael Kerrisk <mtk.manpagesgmail.com> %%%LICENSE_START(VERBATIM) Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Since the Linux kernel and libraries are constantly changing, this manual page may be incorrect or out-of-date. The author(s) assume no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein. The author(s) may not have taken the same level of care in the production of this manual, which is licensed free of charge, as they might when working professionally. Formatted or processed versions of this manual, if unaccompanied by the source, must acknowledge the copyright and authors of this work. %%%LICENSE_END |