File

File is an open source software that implements the file command, which is widely used on various free operating systems such as OpenBSD, Linux and FreeBSD, as well as on systems that rely on free software like OS/2, DOS and MS Windows among others. The file command helps users determine the type of data contained in a file, using words instead of filename extensions to accomplish this task. Unlike MS-Windows, UNIX and other systems analyse the actual contents of a file instead of relying on its file name extension. Although this method may take more time, it is more reliable.

The original file command was only available in binary form until Ian Darwin created his reimplementation of the command. This implementation, including the magic file, was originally written by Ian Darwin and is currently maintained by a team of developers led by Christos Zoulas. File is widely used across different BSD distributions such as FreeBSD, NetBSD, OpenBSD, Darwin/Mac OS X, among others. It is also used in numerous Linux distributions.

The Apache httpd server mod_mime_magic module relies on the file command's innards to improve file type guessing reliability under Apache HTTPD. All these features make File a useful tool for users looking to identify the content of their files on a variety of platforms.