class File
U_R = 0400
U_W = 0200
U_X = 0100
G_R = 0040
G_W = 0020
G_X = 0010
O_R = 0004
O_W = 0002
O_X = 0001
A_R = 0444
A_W = 0222
A_X = 0111
end
open("my_file", "w") {}
File.chmod(File::U_R | File::U_W | File::G_R | File::O_R, "my_file")
File.chmod(File::A_R | File::U_W, "my_file")
File.chmod(0644, "my_file") # Bitmap: 110001001