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 .