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.\" Hey Emacs! This file is -*- nroff -*- source.
.\"
.\" This manpage is Copyright (C) 2006 Jens Axboe
.\" and Copyright (C) 2006 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" 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.\" manual page may be incorrect or out-of-date.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.
.\"
.TH TEE 2 2009-09-15 "Linux" "Linux Programmer's Manual"
.SH NAME
tee \- duplicating pipe content
.SH SYNOPSIS
.nf
.B #define _GNU_SOURCE
.B #include <fcntl.h>
.BI "ssize_t tee(int " fd_in ", int " fd_out ", size_t " len \
", unsigned int " flags );
.fi
.\" Return type was long before glibc 2.7
.SH DESCRIPTION
.\" Example programs http://brick.kernel.dk/snaps
.\"
.\"
.\" add a "tee(in, out1, out2)" system call that duplicates the pages
.\" (again, incrementing their reference count, not copying the data) from
.\" one pipe to two other pipes.
.BR tee ()
duplicates up to
.I len
bytes of data from the pipe referred to by the file descriptor
.I fd_in
to the pipe referred to by the file descriptor
.IR fd_out .
It does not consume the data that is duplicated from
.IR fd_in ;
therefore, that data can be copied by a subsequent
.BR splice (2).
.I flags
is a series of modifier flags, which share the name space with
.BR splice (2)
and
.BR vmsplice (2):
.TP 1.9i
.B SPLICE_F_MOVE
Currently has no effect for
.BR tee ();
see
.BR splice (2).
.TP
.B SPLICE_F_NONBLOCK
Do not block on I/O; see
.BR splice (2)
for further details.
.TP
.B SPLICE_F_MORE
Currently has no effect for
.BR tee (),
but may be implemented in the future; see
.BR splice (2).
.TP
.B SPLICE_F_GIFT
Unused for
.BR tee ();
see
.BR vmsplice (2).
.SH RETURN VALUE
Upon successful completion,
.BR 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
.IR fd_in .
On error,
.BR tee ()
returns \-1 and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EINVAL
.I fd_in
or
.I fd_out
does not refer to a pipe; or
.I fd_in
and
.I fd_out
refer to the same pipe.
.TP
.B ENOMEM
Out of memory.
.SH VERSIONS
The
.BR tee ()
system call first appeared in Linux 2.6.17.
.SH "CONFORMING TO"
This system call is Linux-specific.
.SH NOTES
Conceptually,
.BR tee ()
copies the data between the two pipes.
In reality no real data copying takes place though:
under the covers,
.BR tee ()
assigns data in the output by merely grabbing
a reference to the input.
.SH EXAMPLE
The following example implements a basic
.BR tee (1)
program using the
.BR tee ()
system call.
.nf
#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);
}
.fi
.SH SEE ALSO
.BR splice (2),
.BR vmsplice (2),
.BR feature_test_macros (7)
.SH COLOPHON
This page is part of release 3.27 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
|
