mime_magic('/path/to/mime.types')

    This method sets and/or returns the external magic mime types file to be used for the identification of files via the mime_type method. By default, MIME identification is based upon internal mime types defined within the File::MMagic module.

    See File::MMagic for further details.

mime_type('field')

    This method returns the MIME type of the file uploaded through the form input field named 'field' as determined by file magic numbers. This is the best means by which to validate the nature of the uploaded file.

    See File::MMagic for further details.

File::MMagic - Guess file type

This module is to guess file type from its contents like file(1)
command.