Password protected dmg file-Forgotten password!

Hi everyone,

So i set up a password recently for a folder, and i've now forgotten the password.

The thing is when I was filling it in, I had that bar on the side telling me my password was weak, so i added a few numbers and maybe a symbol onto the end of the password i normally use. I've now forgotten it, but i definitely know the first 8 characters.

Does anyone know how i can run a script to brute force it, using the original 8 characters as the basis?

Thanks