Man:
man command formats and displays the on-line manual pages. If you specify section, man only looks in that section of the manual. name is normally the name of the manual page, which is typically the name of a command, function, or file.
$ man whatis
whatis(1) whatis(1)
NAME
whatis - search the whatis database for complete words.
SYNOPSIS
whatis keyword ...
DESCRIPTION
whatis searches a set of database files containing short descriptions
of system commands for keywords and displays the result on the standard
output. Only complete word matches are displayed.
The whatis database is created using the command /usr/sbin/makewhatis.
AUTHOR
John W. Eaton was the original author of man. Zeyd M. Ben-Halim
released man 1.2, and Andries Brouwer followed up with versions 1.3
thru 1.5p. Federico Lucifredi is the current
maintainer.
SEE ALSO
apropos(1), man(1).
Whatis:
whatis command searches a set of database files containing short descriptions of system commands for keywords and displays the result on the standard output. Only complete word matches are displayed.
$ whatis whatis whatis (1) - search the whatis database for complete words
Apropos:
apropos command searches a set of database files containing short descriptions of system commands for keywords and displays the result on the standard output. You can think apropos as a wrapper for the “man -k” command, useful for one knows the action but does not rememeber the actual command. Simply put, as shown in the below example, returns the indicated man pages that include the term “whatis“.
$ apropos whatis apropos (1) - search the whatis database for strings makewhatis (8) - Create the whatis database man (rpm) - A set of documentation tools: man, apropos and whatis. whatis (1) - search the whatis database for complete words
man, whatis, and apropos are closely related commands that provide similar functionality.