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tee.html
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<!-- Creator : groff version 1.22.4 -->
<!-- CreationDate: Wed Jan 29 11:25:40 2020 -->
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta name="generator" content="groff -Thtml, see www.gnu.org">
<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
<meta name="Content-Style" content="text/css">
<style type="text/css">
p { margin-top: 0; margin-bottom: 0; vertical-align: top }
pre { margin-top: 0; margin-bottom: 0; vertical-align: top }
table { margin-top: 0; margin-bottom: 0; vertical-align: top }
h1 { text-align: center }
</style>
<title>TEE</title>
</head>
<body>
<h1 align="center">TEE</h1>
<a href="#NAME">NAME</a><br>
<a href="#SYNOPSIS">SYNOPSIS</a><br>
<a href="#DESCRIPTION">DESCRIPTION</a><br>
<a href="#RETURN VALUE">RETURN VALUE</a><br>
<a href="#ERRORS">ERRORS</a><br>
<a href="#VERSIONS">VERSIONS</a><br>
<a href="#CONFORMING TO">CONFORMING TO</a><br>
<a href="#NOTES">NOTES</a><br>
<a href="#EXAMPLE">EXAMPLE</a><br>
<a href="#SEE ALSO">SEE ALSO</a><br>
<a href="#COLOPHON">COLOPHON</a><br>
<hr>
<h2>NAME
<a name="NAME"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">tee -
duplicating pipe content</p>
<h2>SYNOPSIS
<a name="SYNOPSIS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>#define
_GNU_SOURCE</b> /* See feature_test_macros(7) */ <b><br>
#include <fcntl.h></b></p>
<p style="margin-left:11%; margin-top: 1em"><b>ssize_t
tee(int</b> <i>fd_in</i><b>, int</b> <i>fd_out</i><b>,
size_t</b> <i>len</i><b>, unsigned int</b>
<i>flags</i><b>);</b></p>
<h2>DESCRIPTION
<a name="DESCRIPTION"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>tee</b>()
duplicates up to <i>len</i> bytes of data from the pipe
referred to by the file descriptor <i>fd_in</i> to the pipe
referred to by the file descriptor <i>fd_out</i>. It does
not consume the data that is duplicated from <i>fd_in</i>;
therefore, that data can be copied by a subsequent
<b>splice</b>(2).</p>
<p style="margin-left:11%; margin-top: 1em"><i>flags</i> is
a bit mask that is composed by ORing together zero or more
of the following values:</p>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="26%">
<p><b>SPLICE_F_MOVE</b></p></td>
<td width="3%"></td>
<td width="60%">
<p>Currently has no effect for <b>tee</b>(); see
<b>splice</b>(2).</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="26%">
<p><b>SPLICE_F_NONBLOCK</b></p></td>
<td width="3%"></td>
<td width="60%">
<p>Do not block on I/O; see <b>splice</b>(2) for further
details.</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="26%">
<p><b>SPLICE_F_MORE</b></p></td>
<td width="3%"></td>
<td width="60%">
<p>Currently has no effect for <b>tee</b>(), but may be
implemented in the future; see <b>splice</b>(2).</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="26%">
<p><b>SPLICE_F_GIFT</b></p></td>
<td width="3%"></td>
<td width="60%">
<p>Unused for <b>tee</b>(); see <b>vmsplice</b>(2).</p></td></tr>
</table>
<h2>RETURN VALUE
<a name="RETURN VALUE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">Upon successful
completion, <b>tee</b>() 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
<i>fd_in</i>.</p>
<p style="margin-left:11%; margin-top: 1em">On error,
<b>tee</b>() returns -1 and <i>errno</i> is set to indicate
the error.</p>
<h2>ERRORS
<a name="ERRORS"></a>
</h2>
<table width="100%" border="0" rules="none" frame="void"
cellspacing="0" cellpadding="0">
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p style="margin-top: 1em"><b>EAGAIN</b></p></td>
<td width="2%"></td>
<td width="78%">
<p style="margin-top: 1em"><b>SPLICE_F_NONBLOCK</b> was
specified in <i>flags</i> or one of the file descriptors had
been marked as nonblocking (<b>O_NONBLOCK</b>)<b>,</b> and
the operation would block.</p></td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>EINVAL</b></p></td>
<td width="2%"></td>
<td width="78%">
<p><i>fd_in</i> or <i>fd_out</i> does not refer to a pipe;
or <i>fd_in</i> and <i>fd_out</i> refer to the same
pipe.</p> </td></tr>
<tr valign="top" align="left">
<td width="11%"></td>
<td width="9%">
<p><b>ENOMEM</b></p></td>
<td width="2%"></td>
<td width="78%">
<p>Out of memory.</p></td></tr>
</table>
<h2>VERSIONS
<a name="VERSIONS"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">The
<b>tee</b>() system call first appeared in Linux 2.6.17;
library support was added to glibc in version 2.5.</p>
<h2>CONFORMING TO
<a name="CONFORMING TO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">This system
call is Linux-specific.</p>
<h2>NOTES
<a name="NOTES"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">Conceptually,
<b>tee</b>() copies the data between the two pipes. In
reality no real data copying takes place though: under the
covers, <b>tee</b>() assigns data to the output by merely
grabbing a reference to the input.</p>
<h2>EXAMPLE
<a name="EXAMPLE"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">The example
below implements a basic <b>tee</b>(1) program using the
<b>tee</b>() system call. Here is an example of its use:</p>
<p style="margin-left:17%; margin-top: 1em">$ <b>date
|./a.out out.log | cat</b> <br>
Tue Oct 28 10:06:00 CET 2014 <br>
$ <b>cat out.log</b> <br>
Tue Oct 28 10:06:00 CET 2014</p>
<p style="margin-left:11%; margin-top: 1em"><b>Program
source</b> <br>
#define _GNU_SOURCE <br>
#include <fcntl.h> <br>
#include <stdio.h> <br>
#include <stdlib.h> <br>
#include <unistd.h> <br>
#include <errno.h> <br>
#include <limits.h></p>
<p style="margin-left:11%; margin-top: 1em">int <br>
main(int argc, char *argv[]) <br>
{ <br>
int fd; <br>
int len, slen;</p>
<p style="margin-left:11%; margin-top: 1em">if (argc != 2)
{ <br>
fprintf(stderr, "Usage: %s <file>\n",
argv[0]); <br>
exit(EXIT_FAILURE); <br>
}</p>
<p style="margin-left:11%; margin-top: 1em">fd =
open(argv[1], O_WRONLY | O_CREAT | O_TRUNC, 0644); <br>
if (fd == -1) { <br>
perror("open"); <br>
exit(EXIT_FAILURE); <br>
}</p>
<p style="margin-left:11%; margin-top: 1em">do { <br>
/* <br>
* tee stdin to stdout. <br>
*/ <br>
len = tee(STDIN_FILENO, STDOUT_FILENO, <br>
INT_MAX, SPLICE_F_NONBLOCK);</p>
<p style="margin-left:11%; margin-top: 1em">if (len < 0)
{ <br>
if (errno == EAGAIN) <br>
continue; <br>
perror("tee"); <br>
exit(EXIT_FAILURE); <br>
} else <br>
if (len == 0) <br>
break;</p>
<p style="margin-left:11%; margin-top: 1em">/* <br>
* Consume stdin by splicing it to a file. <br>
*/ <br>
while (len > 0) { <br>
slen = splice(STDIN_FILENO, NULL, fd, NULL, <br>
len, SPLICE_F_MOVE); <br>
if (slen < 0) { <br>
perror("splice"); <br>
break; <br>
} <br>
len -= slen; <br>
} <br>
} while (1);</p>
<p style="margin-left:11%; margin-top: 1em">close(fd); <br>
exit(EXIT_SUCCESS); <br>
}</p>
<h2>SEE ALSO
<a name="SEE ALSO"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em"><b>splice</b>(2),
<b>vmsplice</b>(2), <b>pipe</b>(7)</p>
<h2>COLOPHON
<a name="COLOPHON"></a>
</h2>
<p style="margin-left:11%; margin-top: 1em">This page is
part of release 5.02 of the Linux <i>man-pages</i> 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/.</p>
<hr>
</body>
</html>