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:
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:
The following environment variables shall affect the execution of man:
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:
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