Provided by: manpages-posix_2.16-1_all 
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.
SEE ALSO
more
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 .