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 — display system documentation
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.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following option shall be supported:
- 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:
The following operand shall be supported:
grep -Ei '
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.
The following environment variables shall affect the execution of man:
- 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.
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
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:
- 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.)
- If set to a non-empty string value, override the values of all the other
- 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.
- Determine the location of message catalogs for the processing of
- 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
- Successful completion.
- An error occurred.
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
- 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
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
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
The Base Definitions volume of POSIX.1‐2017, Chapter
8, Environment Variables, Section 12.2, Utility Syntax
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 .
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