man (1p) - Linux Man Pages
man: display system documentation
PROLOGThis 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 IEEE Std 1003.1-2001, 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
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.
The following operand shall be supported:
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 following environment variables shall affect the execution of man:
- 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.)
- If set to a non-empty string value, override the values of all the other internationalization variables.
- 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 LC_MESSAGES .
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
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.
The following exit values shall be returned:
- Successful completion.
- An error occurred.
CONSEQUENCES OF ERRORS
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
COPYRIGHTPortions 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 .