Ubuntu Manpage: This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

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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

       man — display system documentation

SYNOPSIS

       man [−k] name...

DESCRIPTION

       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 utilities.  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.

OPTIONS

       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 command:

                   grep −Ei '
                   name
                   name
                   ...
                   ' 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.

OPERANDS

       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.

STDIN

       Not used.

INPUT FILES

       None.

ENVIRONMENT VARIABLES

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

LC_MESSAGES
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.

ASYNCHRONOUS EVENTS

       Default.

STDOUT

       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.

STDERR

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

OUTPUT FILES

       None.

EXTENDED DESCRIPTION

       None.

EXIT STATUS

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

CONSEQUENCES OF ERRORS

       Default.

       The following sections are informative.

APPLICATION USAGE

       None.

EXAMPLES

       None.

RATIONALE

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 provision of some portable way of accessing documentation
would aid user portability. The arguments 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 utility. 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 (utilities, functions, file formats, and so on) when the system administrator reveals the
location 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

FUTURE DIRECTIONS

       None.

COPYRIGHT

       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  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.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 .