Ubuntu Manpage: man - display system documentation

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 IEEE Std 1003.1-2001,
       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...

       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 IEEE Std 1003.1-2001, 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 only for diagnostic messages.

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 IEEE Std 1003.1-2001.

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 IEEE Std 1003.1-2001 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 IEEE Std 1003.1-2001-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, 2003 Edition, Standard for Information Technology  --  Portable  Operating  System
       Interface  (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 .