TEE
Section: POSIX Programmer's Manual (1P)
Updated: 2017
Page Index
PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
NAME
tee
--- duplicate standard input
SYNOPSIS
tee [-ai] [file...]
DESCRIPTION
The
tee
utility shall copy standard input to standard output, making a copy in
zero or more files. The
tee
utility shall not buffer output.
If the
-a
option is not specified, output files shall be written (see
Section 1.1.1.4, File Read, Write, and Creation.
OPTIONS
The
tee
utility shall conform to the Base Definitions volume of POSIX.1-2017,
Section 12.2,
Utility Syntax Guidelines.
The following options shall be supported:
- -a
-
Append the output to the files.
- -i
-
Ignore the SIGINT signal.
OPERANDS
The following operands shall be supported:
- file
-
A pathname of an output file. If a
file
operand is
'-',
it shall refer to a file named
-;
implementations shall not treat it as meaning standard output.
Processing of at least 13
file
operands shall be supported.
STDIN
The standard input can be of any type.
INPUT FILES
None.
ENVIRONMENT VARIABLES
The following environment variables shall affect the execution of
tee:
- LANG
-
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1-2017,
Section 8.2, Internationalization Variables
for the precedence of internationalization variables used to determine
the values of locale categories.)
- LC_ALL
-
If set to a non-empty string value, override the values of all the
other internationalization variables.
- LC_CTYPE
-
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
- LC_MESSAGES
-
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
- NLSPATH
-
Determine the location of message catalogs for the processing of
LC_MESSAGES.
ASYNCHRONOUS EVENTS
Default, except that if the
-i
option was specified, SIGINT shall be ignored.
STDOUT
The standard output shall be a copy of the standard input.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
If any
file
operands are specified, the standard input shall be copied to each
named file.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
- 0
-
The standard input was successfully copied to all output files.
- >0
-
An error occurred.
CONSEQUENCES OF ERRORS
If a write to any successfully opened
file
operand fails, writes to other successfully opened
file
operands and standard output shall continue, but the exit status shall
be non-zero. Otherwise, the default actions specified in
Section 1.4,
Utility Description Defaults
apply.
The following sections are informative.
APPLICATION USAGE
The
tee
utility is usually used in a pipeline, to make a copy of the output of
some utility.
The
file
operand is technically optional, but
tee
is no more useful than
cat
when none is specified.
EXAMPLES
Save an unsorted intermediate form of the data in a pipeline:
-
... | tee unsorted | sort > sorted
RATIONALE
The buffering requirement means that
tee
is not allowed to use ISO C standard fully buffered or line-buffered writes. It
does not mean that
tee
has to do 1-byte reads followed by 1-byte writes.
It should be noted that early versions of BSD ignore any invalid
options and accept a single
'-'
as an alternative to
-i.
They also print a message if unable to open a file:
-
"tee: cannot access %s\n", <pathname>
Historical implementations ignore write errors. This is explicitly not
permitted by this volume of POSIX.1-2017.
Some historical implementations use O_APPEND when providing append
mode; others use the
lseek()
function to seek to the end-of-file after opening the file without
O_APPEND. This volume of POSIX.1-2017 requires functionality equivalent to using O_APPEND;
see
Section 1.1.1.4, File Read, Write, and Creation.
FUTURE DIRECTIONS
None.
SEE ALSO
Chapter 1,
Introduction,
cat
The Base Definitions volume of POSIX.1-2017,
Chapter 8, Environment Variables,
Section 12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1-2017,
lseek()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .