sub safe_open {
    my $fn = shift;
    my $fh = do { local *FH };
    my ($mode, $result);
    if ($fn =~ /^>[^>]/) {
        $mode = 1;
    }
    elsif ($fn =~ /^>>/) {
        $mode = 2;
    }
    else {
        $mode = 0;
    }

    if ($mode == 1 and $flock_enabled) {
        # Write mode with flock.
        $truncate_please = 1;
        my $fhtemp = do { local *FHT };
        $result = open( $fhtemp, "+>>$fn" );
        if ($result) {
             $result = open($filehandle, ">&$fhtemp" );
             close($fhtemp);
        }
    }
    elsif ($mode == 1) {
        # Write mode without flock.
        $result = open($fh, ">$fn");
    }
    elsif ($mode == 2) {
        # Append mode.
        $result = open($fh, ">>$fn");
    }
    elsif ($mode == 0) {
        $result = open($fh, $fn);
    }
    unless ($result) {
        # Open failed.
        fatal_error("Couldn't open $fn.");
    }
    flock($fh, 2) if $flock_enabled;
    if ($truncate_please) {
        truncate($fh, 0) or fatal_error("Could not truncate file $fn.");
    }
    return $fh;
}