file

Determine file type. More information: https://manned.org/file.

Give a description of the type of the specified file. Works fine for files with no file extension:

file {{filename}}
Look inside a zipped file and determine the file type(s) inside:

file -z {{foo.zip}}
Allow file to work with special or device files:

file -s {{filename}}
Don't stop at first file type match; keep going until the end of the file:

file -k {{filename}}
Determine the mime encoding type of a file:

file -i {{filename}}