This is a program that examines a file and attempts to determine what it is. It is similar to the posix file(1) command but gives more detail and recognizes a wider variety of file types. (There are occasions when whatis recognizes that file could give more information, and calls the latter program.)
Note: This program has an unfortunate name collision with the posix program, whatis(1). You can easily rename the program when you download it.
$ whatis index.html WHATIS - Version 2.58 Copyright 1989-2011, Glenn Story File: /home/glenn/websites/personal/tools/index.html File-system analysis indicates EXT2 or EXT3 file system File-mode analysis indicates regular file File extension (.html) indicates Hyper-Text Markup Language file File analysis indicates DOS/Windows ASCII Text file Text analysis indicates HyperText Markup Language (HTML) file