file 5.03-5ubuntu1 (amd64 binary) in ubuntu lucid

 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.