use Fcntl qw(O_CREAT O_EXCL O_APPEND O_RDWR);

if (sysopen(CREATE, $log, O_APPEND|O_RDWR|O_EXCL|O_CREAT)) {
    ... CREATE is now open, do something with it ...
} else {
    warn("Unable to open log file '$log': $!.\n");
}