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
File Read, Write, and Creation .
OPTIONS
The tee utility shall conform to the Base Definitions volume of
IEEE Std 1003.1-2001, 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. 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
IEEE Std 1003.1-2001, 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 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 IEEE Std 1003.1-2001.
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 IEEE Std 1003.1-2001
requires functionality equivalent to using O_APPEND; see File Read,
Write, and Creation .
FUTURE DIRECTIONS
None.
SEE ALSO
Introduction , cat , the System Interfaces volume of
IEEE Std 1003.1-2001, lseek()
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 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 .