TEE(1P) POSIX Programmer's Manual TEE(1P)
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.
tee -- duplicate standard input
tee [-ai] [file...]
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 22.214.171.124,
File Read, Write, and Creation.
The tee utility shall conform to the Base Definitions volume of POSIX.1-2008, Section
12.2, Utility Syntax Guidelines.
The following options shall be supported:
-a Append the output to the files.
-i Ignore the SIGINT signal.
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. Pro-
cessing of at least 13 file operands shall be supported.
The standard input can be of any type.
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.1-2008, Section 8.2, Interna-
tionalization 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 inter-
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
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.
Default, except that if the -i option was specified, SIGINT shall be ignored.
The standard output shall be a copy of the standard input.
The standard error shall be used only for diagnostic messages.
If any file operands are specified, the standard input shall be copied to each named file.
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
The following sections are informative.
The tee utility is usually used in a pipeline, to make a copy of the output of some util-
The file operand is technically optional, but tee is no more useful than cat when none is
Save an unsorted intermediate form of the data in a pipeline:
... | tee unsorted | sort > sorted
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 fol-
lowed by 1-byte writes.
It should be noted that early versions of BSD ignore any invalid options and accept a sin-
gle '-' 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.1-2008.
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.1-2008 requires functionality equivalent to using O_APPEND; see Section
126.96.36.199, File Read, Write, and Creation.
Chapter 1, Introduction, cat
The Base Definitions volume of POSIX.1-2008, Chapter 8, Environment Variables, Section
12.2, Utility Syntax Guidelines
The System Interfaces volume of POSIX.1-2008, lseek()
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the event of any discrep-
ancy 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.unix.org/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 man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 TEE(1P)