posix man page for tee

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

PROLOG
       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing 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.1-2008, 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.1-2008, 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  con-
       tinue, 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
", <pathname>

       Historical implementations ignore write errors. This is explicitly not permitted by this volume of POSIX.1-2008.

       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.1-2008 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.1-2008, Chapter 8, Environment Variables, Section 12.2, Utility Syntax Guidelines

       The System Interfaces volume of POSIX.1-2008, lseek()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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						       2013								   TEE(1P)