DouKaku?

module doukaku;
private import std.stream;
void remove_comments(BufferedFile in_f, BufferedFile out_f) {
    foreach(char[] line; in_f) {
        if (line[0] != '#')
            out_f.writeLine(line);
    }
}

void main() {
    BufferedFile in_f = new BufferedFile("10.input", FileMode.In);
    BufferedFile out_f = new BufferedFile("10.output", FileMode.OutNew);
    remove_comments(in_f, out_f);
    in_f.close();
    out_f.close();
}