( string filename )
Returns the group ID of the file, or FALSE in case
of an error. The group ID is returned in numerical format, use
posix_getgrgid() to resolve it to a group name.
Upon failure, FALSE is returned along with an error of level
Note: The results of this
function are cached. See clearstatcache() for
Tip: As of PHP 5.0.0 this function
can also be used with some URL wrappers. Refer to
Appendix M for a listing of which wrappers support
stat() family of functionality.
See also fileowner(), and