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 1.1.1.4 File Read, Write, and Creation).

OPTIONS

The tee utility shall conform to XBD 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 XBD 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

^[XSI] Determine the location of messages objects and message catalogs.

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 1.4 Utility Description Defaults apply.

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.1-2024.

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.1-2024 requires functionality equivalent to using O_APPEND; see 1.1.1.4 File Read, Write, and Creation.

FUTURE DIRECTIONS

If this utility is directed to create a new directory entry that contains any bytes that have the encoded value of a <newline> character, implementations are encouraged to treat this as an error. A future version of this standard may require implementations to treat this as an error.

SEE ALSO

1. Introduction, cat

XBD 8. Environment Variables, 12.2 Utility Syntax Guidelines

XSH lseek

CHANGE HISTORY

First released in Issue 2.

Issue 6

IEEE PASC Interpretation 1003.2 #168 is applied.

Issue 7

Austin Group Interpretation 1003.1-2001 #092 is applied.

SD5-XCU-ERN-97 is applied, updating the SYNOPSIS.

Issue 8

Austin Group Defect 251 is applied, encouraging implementations to disallow the creation of filenames containing any bytes that have the encoded value of a <newline> character.

Austin Group Defect 1122 is applied, changing the description of NLSPATH .

Austin Group Defect 1494 is applied, inserting a missing closing parenthesis.