file 4.16-0ubuntu3.2 (amd64 binary) in ubuntu dapper

 File tests each argument in an attempt to classify it. There are three
 sets of tests, performed in this order: filesystem tests, magic number
 tests, and language tests. The first test that succeeds causes the
 file type to be printed.
 .
 Starting with version 4, the file command is not much more than a wrapper
 around the "magic" library.