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TEE

Section: User Commands (1)
Updated: January 2018
Index Return to Main Contents

NAME

tee - read from standard input and write to standard output and files

SYNOPSIS

tee [,OPTION/]... [,FILE/]...

DESCRIPTION

Copy standard input to each FILE, and also to standard output.

-a, --append: append to the given FILEs, do not overwrite
-i, --ignore-interrupts: ignore interrupt signals
-p: diagnose errors writing to non pipes
--output-error[=,MODE/]: set behavior on write error. See MODE below
--help: display this help and exit
--version: output version information and exit

MODE determines behavior with write errors on the outputs:

'warn': diagnose errors writing to any output
'warn-nopipe': diagnose errors writing to any output not a pipe
'exit': exit on error writing to any output
'exit-nopipe': exit on error writing to any output not a pipe

The default MODE for the -p option is 'warn-nopipe'. The default operation when --output-error is not specified, is to exit immediately on error writing to a pipe, and diagnose errors writing to non pipe outputs.

AUTHOR

Written by Mike Parker, Richard M. Stallman, and David MacKenzie.

REPORTING BUGS

GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Report tee translation bugs to <http://translationproject.org/team/>

COPYRIGHT

Copyright © 2017 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law.

Index

NAME

SYNOPSIS

DESCRIPTION

MODE determines behavior with write errors on the outputs:

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Time: 04:45:26 GMT, September 16, 2022 Content-type: text/html; charset=UTF-8 Man page of TEE

TEE

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index Return to Main Contents

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 bit mask that is composed by ORing together zero or more of the following values:

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 copying takes place though: under the covers, tee() assigns data to the output by merely grabbing a reference to the input.

EXAMPLE

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

Program source

#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); }

COLOPHON

This page is part of release 4.15 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/.