| TEE(2) - phpMan
TEE(2) Linux Programmer's Manual TEE(2)
NAME
tee - duplicating pipe content
SYNOPSIS
#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);
DESCRIPTION
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 series of modifier flags, which share the name space with splice(2) and
vmsplice(2):
SPLICE_F_MOVE Currently has no effect for tee(); see splice(2).
SPLICE_F_NONBLOCK Do not block on I/O; see splice(2) for further details.
SPLICE_F_MORE Currently has no effect for tee(), but may be implemented in the
future; see splice(2).
SPLICE_F_GIFT Unused for tee(); see vmsplice(2).
RETURN VALUE
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.
ERRORS
EAGAIN SPLICE_F_NONBLOCK was specified in flags, and the operation would block.
EINVAL fd_in or fd_out does not refer to a pipe; or fd_in and fd_out refer to the same
pipe.
ENOMEM Out of memory.
VERSIONS
The tee() system call first appeared in Linux 2.6.17; library support was added to glibc
in version 2.5.
CONFORMING TO
This system call is Linux-specific.
NOTES
Conceptually, tee() copies the data between the two pipes. In reality no real data copy‐
ing takes place though: under the covers, tee() assigns data in the output by merely grab‐
bing a reference to the input.
EXAMPLE
The following example implements a basic tee(1) program using the tee() system call.
#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);
}
SEE ALSO
splice(2), vmsplice(2)
COLOPHON
This page is part of release 3.74 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 http://www.kernel.org/doc/man-pages/.
Linux 2014-07-08 TEE(2)
|