TEE(1)                     POSIX Programmer's Manual                    TEE(1)



PROLOG
       This manual page is part of the POSIX Programmer's Manual.  The OS
       implementation of this interface may differ (consult the corresponding
       OS manual page for details of OS behavior), or the interface may not be
       implemented on OS.

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", <pathname>

       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 .



IEEE/The Open Group                  2017                               TEE(1)
