use Fcntl qw(:DEFAULT :flock);
# assume $flock_enabled set accordingly

sub safe_open {
    my $fn = shift;
    $fn =~ s/^(>>?)//;
    $mode = length($1);
    my $flags = $mode == 1 ? O_CREAT | O_WRONLY | O_TRUNC  :
                $mode == 2 ? O_CREAT | O_WRONLY | O_APPEND :
                O_RDONLY;
    sysopen(my $fh, $fn, $flags) || die "Can't open $fn: $!";
    flock($fh, LOCK_EX) || die "Can't flock $fn: $!" if $flock_enabled;
    return $fh;
}