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 E_WARNING.
Note: The results of this function are cached. See clearstatcache() for more details.
Tip: As of PHP 5.0.0 this function can also be used with some URL wrappers. Refer to Appendix L for a listing of which wrappers support stat() family of functionality.
See also fileowner(), and safe_mode_gid.