Sends SIGINFO to the process. This is a BSD feature OS X inherited. You must have the terminal window executing dd selected when entering CTRL + T for this to work.
pv -tpreb /dev/sda | dd of=/dev/sdb bs=1M
Your platform may not have pv by default. If you are using Homebew on OSX, simply 'brew install pv'.
while pgrep ^dd; do pkill -INFO dd; sleep 10; done
While a dd is running in one terminal, open another and enter the while loop. The sample output will be displayed in the window running the dd and the while loop will exit when the dd is complete. It's possible that a "sudo" will need to be inserted before "pkill", depending on your setup, for example: