sub fixdir {
    my $dir = shift;
    opendir my $DH, $dir or die "Cannot open '$dir': $!";

    while (my $f = readdir $DH) {
        next if grep $_ eq $f, qw/. ../;
        (my $new = $f) =~ s/[^a-zA-Z0-9_.]/_/g;
        if ($new ne $f) {
            $new .= '1' while -e "$dir/$new";

            print STDERR "Renaming: $f -> $new\n";
            rename "$dir/$f", "$dir/$new"; 
        }

        fixdir("$dir/$new") if -d "$dir/$new";
    }
}