The file utility shall perform a series of tests in sequence on
each specified file in an attempt to classify it:
1. If file does not exist, cannot be read, or its file status
could not be determined, the output shall indicate that the
file was processed, but that its type could not be
determined.
2. If the file is not a regular file, its file type shall be
identified. The file types directory, FIFO, socket, block
special, and character special shall be identified as such.
Other implementation-defined file types may also be
identified. If file is a symbolic link, by default the link
shall be resolved and file shall test the type of file
referenced by the symbolic link. (See the -h and -i options
below.)
3. If the length of file is zero, it shall be identified as an
empty file.
4. The file utility shall examine an initial segment of file and
shall make a guess at identifying its contents based on
position-sensitive tests. (The answer is not guaranteed to be
correct; see the -d, -M, and -m options below.)
5. The file utility shall examine file and make a guess at
identifying its contents based on context-sensitive default
system tests. (The answer is not guaranteed to be correct.)
6. The file shall be identified as a data file.
If file does not exist, cannot be read, or its file status could
not be determined, the output shall indicate that the file was
processed, but that its type could not be determined.
If file is a symbolic link, by default the link shall be resolved
and file shall test the type of file referenced by the symbolic
link.
