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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 β display system documentation
man [βk] 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 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.
The man utility shall conform to the Base Definitions volume of
POSIX.1β2008, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
ββk 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 ββEi '
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 ββEi 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 following operand shall be supported:
name A keyword or the name of a standard utility. When ββk is not
specified and name does not represent one of the standard
utilities, the results are unspecified.
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.1β2008, 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.
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
PAGER Determine an output filtering command for writing the output
to a terminal. Any string acceptable as a command_string
operand to the sh ββc 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 ββk is specified, lines
from the summary database. The format of this text is implementation-
The standard error shall be used for diagnostic messages, and may also
be used for informational messages of unspecified format.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
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 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 ββf option was considered, but due to implementation differences, it
was not included in this volume of POSIX.1β2008.
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.1β2008 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.1β2008βlocale-
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 ββ Display system documentation
ps ββ Report process status
The Base Definitions volume of POSIX.1β2008, 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 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
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