How to use whatis command in Linux.

-d, –debug

Print debugging information.

-v, –verbose

Print verbose warning messages.

-r, –regex

Interpret each name as a regular expression. If a name matches any part of a page name, a match will be made. This option causes whatis to be somewhat slower due to the nature of database searches.

-w, –wildcard

Interpret each name as a pattern containing shell style wildcards. For a match to be made, an expanded name must match the entire page name. This option causes whatis to be somewhat slower due to the nature of database searches.

-l, –long

Do not trim output to the terminal width. Normally, output will be truncated to the terminal width to avoid ugly results from poorly-written NAME sections.

-s list, –sections list,
–section list

Search only the given manual sections. The list is a colon-separated or comma-separated list of sections. If an entry in list is a simple section, for example “3“, then the displayed list of descriptions will include pages in sections “3“, “3perl“, “3x“, and so on; while if an entry in list has an extension, for example “3perl“, then the list only includes pages in that exact part of the manual section.

-m system[,…],
–systems=system[,…]

If this system has access to other operating system’s manual page names, they can be accessed using this option. To search NewOS’s manual page names, use the option “-m NewOS“.

The system specified is a combination of comma delimited operating system names. To include a search of the native operating system’s manual page names, include the system name man in the argument string. This option overrides the $SYSTEM environment variable.

-M path,
–manpath=path

Specify an alternate set of colon-delimited manual page hierarchies to search. By default, whatis uses the $MANPATH environment variable, unless it is empty or unset, in which case it will determine an appropriate manpath based on your $PATH environment variable. This option overrides the contents of $MANPATH.

-L locale,
–locale=locale

Whatis will normally determine your current locale by a call to the C function setlocale which interrogates various environment variables, possibly including $LC_MESSAGES and $LANG. To temporarily override the determined value, use this option to supply a locale string directly to whatis. Note that it will not take effect until the search for pages actually begins. Output such as the help message always displays in the initially determined locale.

-C file, –config-file=file

Use this user configuration file rather than the default of ~/.manpath.

-h, –help

Print a help message and exit.

-V, –version

Display version information.

0

Successful program execution.

1

Usage, syntax or configuration file error.

2

Operational error.

16

Nothing was found that matched the criteria specified.

SYSTEM

If $SYSTEM is set, it has the same effect as if it had been specified as the argument to the -m option.

MANPATH

If $MANPATH is set, its value is interpreted as the colon-delimited manual page hierarchy search path to use.

MANWIDTH

If $MANWIDTH is set, its value is used as the terminal width (see the –long option). If it is not set, the terminal width will be calculated using an ioctl if available, the value of $COLUMNS, or falling back to 80 charac