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.TH MAN "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"

.SH 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.

.SH NAME

man

\(em display system documentation

.SH SYNOPSIS

.LP

.nf

man \fB[\fR\(mik\fB] \fIname\fR...

.fi

.SH DESCRIPTION

The

.IR man

utility shall write information about each of the

.IR name

operands. If

.IR name

is the name of a standard utility,

.IR 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

.IR man

utility shall provide it in an implementation-defined manner.

.P

An implementation may provide information for values of

.IR 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.

.SH OPTIONS

The

.IR man

utility shall conform to the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 12.2" ", " "Utility Syntax Guidelines".

.P

The following option shall be supported:

.IP "\fB\(mik\fP" 8

Interpret

.IR 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:

.RS 8 

.sp

.RS 4

.nf

\fB

grep \(miEi '

\fIname

name\fP

\&...

\&' \fIsummary-database\fR

.fi \fR

.P

.RE

.P

This assumes that the

.IR summary-database

is a text file with a single entry per line; this organization is not

required and the example using

.IR grep

.BR \(miEi

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.

.RE

.SH OPERANDS

The following operand shall be supported:

.IP "\fIname\fR" 10

A keyword or the name of a standard utility. When

.BR \(mik

is not specified and

.IR name

does not represent one of the standard utilities, the results are

unspecified.

.SH STDIN

Not used.

.SH "INPUT FILES"

None.

.SH "ENVIRONMENT VARIABLES"

The following environment variables shall affect the execution of

.IR man :

.IP "\fILANG\fP" 10

Provide a default value for the internationalization variables that are

unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,

.IR "Section 8.2" ", " "Internationalization Variables"

for the precedence of internationalization variables used to determine

the values of locale categories.)

.IP "\fILC_ALL\fP" 10

If set to a non-empty string value, override the values of all the

other internationalization variables.

.IP "\fILC_CTYPE\fP" 10

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

.IR LC_CTYPE

need not affect the format of the information written about the

.IR name

operands.

.IP "\fILC_MESSAGES\fP" 10

.br

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.

.IP "\fINLSPATH\fP" 10

Determine the location of message catalogs for the processing of

.IR LC_MESSAGES .

.IP "\fIPAGER\fP" 10

Determine an output filtering command for writing the output to a

terminal. Any string acceptable as a

.IR command_string

operand to the

.IR sh

.BR \(mic

command shall be valid. When standard output is a terminal device, the

reference page output shall be piped through the command. If the

.IR PAGER

variable is null or not set, the command shall be either

.IR more

or another paginator utility documented in the system documentation.

.SH "ASYNCHRONOUS EVENTS"

Default.

.SH STDOUT

The

.IR man

utility shall write text describing the syntax of the utility

.IR name ,

its options and its operands, or, when

.BR \(mik

is specified, lines from the summary database. The format of this text

is implementation-defined.

.SH STDERR

The standard error shall be used for diagnostic messages, and may also

be used for informational messages of unspecified format.

.SH "OUTPUT FILES"

None.

.SH "EXTENDED DESCRIPTION"

None.

.SH "EXIT STATUS"

The following exit values shall be returned:

.IP "\00" 6

Successful completion.

.IP >0 6

An error occurred.

.SH "CONSEQUENCES OF ERRORS"

Default.

.LP

.IR "The following sections are informative."

.SH "APPLICATION USAGE"

None.

.SH EXAMPLES

None.

.SH RATIONALE

It is recognized that the

.IR 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

.IR 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:

.IP " *" 4

Large quantities of documentation should not be required on a system

that does not have excess disk space.

.IP " *" 4

The current manual system does not present information in a manner that

greatly aids user portability.

.IP " *" 4

A ``better help system'' is currently an area in which vendors feel

that they can add value to their POSIX implementations.

.P

The

.BR \(mif

option was considered, but due to implementation differences, it was

not included in this volume of POSIX.1\(hy2008.

.P

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.

.P

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\(hy2008 for each utility.

These titles are similar to those used in historical systems for this

purpose.

.P

See

.IR mailx

for rationale concerning the default paginator.

.P

The caveat in the

.IR 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

.IR LC_CTYPE

does not necessarily translate the reference page into another

language. This is equivalent to the current state of

.IR LC_MESSAGES

in POSIX.1\(hy2008\(emlocale-specific messages are not yet a requirement.

.P

The historical

.IR 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

.IR man

executable. The standard developers considered the portability of

reference pages to be outside their scope of work. However, users

should be aware that

.IR 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.

.P

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:

.sp

.RS 4

.nf

\fB

man \(em Display system documentation

ps \(em Report process status

.fi \fR

.P

.RE

.SH "FUTURE DIRECTIONS"

None.

.SH "SEE ALSO"

.IR "\fImore\fR\^"

.P

The Base Definitions volume of POSIX.1\(hy2008,

.IR "Chapter 8" ", " "Environment Variables",

.IR "Section 12.2" ", " "Utility Syntax Guidelines"

.SH COPYRIGHT

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 files to

man page format. To report such errors, see

https://www.kernel.org/doc/man-pages/reporting_bugs.html .