tee (1p) - Linux Man Page
tee: duplicate standard input
$ man 1p tee
PROLOGThis 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.
NAMEtee - duplicate standard input
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.
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:
- Append the output to the files.
Ignore the SIGINT signal.
The following operands shall be supported:
A pathname of an output file. Processing of at least 13 file
operands shall be supported.
The following environment variables shall affect the execution of tee:
- 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.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- 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).
- Determine the locale that should be used to affect the format and contents of diagnostic messages written to standard error.
Determine the location of message catalogs for the processing of LC_MESSAGES
The following exit values shall be returned:
- The standard input was successfully copied to all output files.
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 tee utility is usually used in a pipeline, to make a copy of the output of some utility.
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 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 .
COPYRIGHTPortions 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 .
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