If someone sends me a document (.pdf,.doc,.xls, ppt, .ogg, mp3, png, etc) without the extension, how can I determine the file type? The /usr/bin/file command doesn't always guess right or it simply says that I have a Microsoft Office document. I would like to know exactly so I can add the extension to the file name.
You can come up with your own rules by adding them to /etc/magic
man file for more details. It is tricky to always get these correct however, I have had reasonable success.