Otherwise I wouldn't know why it doesn't work while a simple file does. They should use the same magic database in the end.
First, trusting the mime-type from the client is very dangerous.
On Fedora, the php-pear-Fileinfo package uses the same magic file
that the command line file command uses.
If you compile the fileinfo extension separately, you might be using
a different magic file, which might provide inconsistent results.
I have seen /usr/share/misc/magic ( default for fileinfo upstream )
and /usr/share/file/magic ( default for Fedora ).
You also need to use the same flags or options.
Using the PHP fileinfo functions, there are options you pass
( FILEINFO_MIME ) in order to get the output you want.
Using the file command, there are flags you pass ( -i ) in order to
get the output you want.
The defaults are different between the two.
For example, these options should give the same between <?php finfo_file() ?> and file from the command line -
file -biLz filename finfo_file($finfo,"filename",1046)
You need to add the integer values of the FILEINFO_* options
-b is the default for finfo_file() -i == FILEINFO_MIME or 1040 -L == FILEINFO_SYMLINK or 2 -z == FILEINFO_COMPRESS or 4
-k == FILEINFO_CONTINUE or 32, which is mutually exclusive of
FILEINFO_MIME
That is, you can't use FILEINFO_CONTINUE and FILEINFO_MIME together,
is is either one of the other.
Sometimes using FILEINFO_CONTINUE and parsing that string gives you
more information than FILEINFO_MIME does, but that parsing is harder
and more complicated.
if finfo_file($finfo,"filename",1040) returns a gzip or zip mime-type, you could then do
finfo_file($finfo,"filename",1044)
to see what type of data is inside that compressed file.
HTH