Extensions of the UNIX File Command and Magic File for File Type ...

Figure 5. Display of File Types Identified by the File Type Identifier.The reason that only two PUIDs are shown in Fig. 5 is that the File Type Identifier recognizesmany more types of archive files than are registered in the PRONOM registry.The parameters of the file command are used to exclude the file command’s procedural tests.These include tests for the character set of text files, the language of a text file, tar files, EMXapplication type, compound document files and elf files. There are several reasons fortemporarily excluding these procedural tests. First, many of these tests result not in file typeidentification but additional description or metadata extraction.Secondly, the recognition of character sets should be possible with a finite state acceptor. Finitestate acceptors are equivalent in recognition power to regular expressions, and the magiclanguage supports tests of the content of lines of text using regular expressions. An extension ofthe regular expressions tests to multiple lines might accomplish the recognition of character sets.14