When installing 12.10 from 12.04 I am asked for login and password then get `macbook pro ~$`

When installing 12.10 from 12.04 I am asked for login and password then
get `macbook pro ~$`

What do I do when I get the line ~$. What does it mean and how can I
install 12.10 successfully on my macbook pro which had ubuntu 12.04 before
upgrade to 12.10?