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", <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(1POSIX)