if (!-e "$log"){
    open(CREATE, "+>>$log") or die "$log failed: $!\n";
    while (<CREATE>){
        foreach $ser(@ser) {
            printf "%3s",$ser;
        }

        print "\n";
    }

    close(CREATE);
}

##</code><code>##

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");
}

##</code><code>##

... open CREATE ...
foreach my $ser (@ser) {
    printf CREATE "%3s", $ser;
}