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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.1‐2017, 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.1‐2017, 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.1‐2017.
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.1‐2017 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.
SEE ALSO
more
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section
12.2, Utility Syntax Guidelines
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1-2017, Standard for Information Technology -- Portable Operating System Interface
(POSIX), The Open Group Base Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .
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 .