--- name: "tee" section: "1p" platform: "linux" package: "man-pages" version: "6.19-1" release: "Arch Linux 2026-11-01" platforms: ["linux"] url: "https://new.carta.tech/tee/1p" --- # tee(1p) duplicate standard input ## 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", ``` 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 man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting\_bugs.html .