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

       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.

       man -- display system documentation

       man [-k] name...

       The  man  utility  shall write information about each of the name operands. If name is the
       name of a standard utility, man at a minimum shall write a message describing  the  syntax
       used by the standard utility, its options, and operands. If more information is available,
       the man utility shall provide it in an implementation-defined manner.

       An implementation may provide information for values of name other than the standard util-
       ities.  Standard  utilities  that are listed as optional and that are not supported by the
       implementation either shall cause a brief message indicating that fact to be displayed  or
       shall cause a full display of information as described previously.

       The  man  utility  shall  conform  to the Base Definitions volume of POSIX.1-2008, Section
       12.2, Utility Syntax Guidelines.

       The following option shall be supported:

       -k      Interpret name operands as keywords to be used in searching  a  utilities  summary
	       database  that  contains a brief purpose entry for each standard utility and write
	       lines from the summary database that match any of the keywords. The keyword search
	       shall  produce results that are the equivalent of the output of the following com-

		   grep -Ei '
		   ' summary-database

	       This assumes that the summary-database is a text file  with  a  single  entry  per
	       line;  this  organization is not required and the example using grep -Ei is merely
	       illustrative of the type of search intended. The purpose entry to be  included  in
	       the database shall consist of a terse description of the purpose of the utility.

       The following operand shall be supported:

       name	 A  keyword  or the name of a standard utility. When -k is not specified and name
		 does not represent one of the standard utilities, the results are unspecified.

       Not used.


       The following environment variables shall affect the execution of man:

       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, Interna-
		 tionalization 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 inter-
		 nationalization 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 and in the summary database). The value of LC_CTYPE	need  not  affect
		 the format of the information written about the name operands.

		 Determine  the  locale  that should be used to affect the format and contents of
		 diagnostic messages written to standard error and informative	messages  written
		 to standard output.

       NLSPATH	 Determine the location of message catalogs for the processing of LC_MESSAGES.

       PAGER	 Determine  an output filtering command for writing the output to a terminal. Any
		 string acceptable as a command_string operand to the  sh  -c  command	shall  be
		 valid.  When  standard  output  is  a terminal device, the reference page output
		 shall be piped through the command. If the PAGER variable is null  or	not  set,
		 the  command shall be either more or another paginator utility documented in the
		 system documentation.


       The man utility shall write text describing the syntax of the utility  name,  its  options
       and its operands, or, when -k is specified, lines from the summary database. The format of
       this text is implementation-defined.

       The standard error shall be used for diagnostic messages, and may also be used for  infor-
       mational messages of unspecified format.



       The following exit values shall be returned:

	0    Successful completion.

       >0    An error occurred.


       The following sections are informative.



       It  is  recognized  that  the  man utility is only of minimal usefulness as specified. The
       opinion of the standard developers was strongly divided as  to  how  much  or  how  little
       information  man  should be required to provide. They considered, however, that the provi-
       sion of some portable way of accessing documentation would aid user portability. The argu-
       ments against a fuller specification were:

	*  Large  quantities  of  documentation  should not be required on a system that does not
	   have excess disk space.

	*  The current manual system does not present information in a manner that  greatly  aids
	   user portability.

	*  A  ``better help system'' is currently an area in which vendors feel that they can add
	   value to their POSIX implementations.

       The -f option was considered, but due to implementation differences, it was  not  included
       in this volume of POSIX.1-2008.

       The description was changed to be more specific about what has to be displayed for a util-
       ity. The standard developers considered it insufficient to allow a  display  of	only  the
       synopsis without giving a short description of what each option and operand does.

       The  ``purpose''  entry to be included in the database can be similar to the section title
       (less the numeric prefix) from this volume of POSIX.1-2008 for each utility.  These titles
       are similar to those used in historical systems for this purpose.

       See mailx for rationale concerning the default paginator.

       The  caveat  in the LC_CTYPE description was added because it is not a requirement that an
       implementation provide reference pages for all of its supported locales	on  each  system;
       changing LC_CTYPE does not necessarily translate the reference page into another language.
       This is equivalent to the current state of  LC_MESSAGES	in  POSIX.1-2008--locale-specific
       messages are not yet a requirement.

       The  historical	MANPATH  variable  is not included in POSIX because no attempt is made to
       specify naming conventions for reference page files, nor even to  mandate  that	they  are
       files  at all. On some implementations they could be a true database, a hypertext file, or
       even fixed strings within the man  executable.  The  standard  developers  considered  the
       portability of reference pages to be outside their scope of work. However, users should be
       aware that MANPATH is implemented on a number of historical systems and	that  it  can  be
       used  to tailor the search pattern for reference pages from the various categories (utili-
       ties, functions, file formats, and so on) when the system administrator reveals the  loca-
       tion and conventions for reference pages on the system.

       The  keyword search can rely on at least the text of the section titles from these utility
       descriptions, and the implementation may add more keywords. The	term  ``section  titles''
       refers to the strings such as:

	   man -- Display system documentation
	   ps -- Report process status



       The  Base  Definitions  volume  of POSIX.1-2008, Chapter 8, Environment Variables, Section
       12.2, Utility Syntax Guidelines

       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2013  Edition,	Standard  for Information Technology -- 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  discrep-
       ancy  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.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					  MAN(1P)
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