The specification for "chgrp" is as specified in the SUS but with the following differences as listed below.
like verbose but report only when a change is made
affect the referent of each symbolic link, rather than the symbolic link itself
affect symbolic links instead of any referenced file (available only on systems that can change the ownership of a symlink)
suppress most error messages
use RFILE's group rather than the specified GROUP value
output a diagnostic for every file processed
output version information and exit