$str = "auth_plugin_stack = a,b,EXT::USCC::USCCAuth,c,d";
print "$str \n";
$str =~ s/((\w+::)+\w+,)//;
print "$str \n";

##</code><code>##

auth_plugin_stack = a,b,EXT::USCC::USCCAuth,c,d 
auth_plugin_stack = a,b,c,d