To use the scripts you will need pv but you probably want to install lzop and xz as well. On OS X you can install all of them via:
brew install pv lzop xz
To save an SD card image:
imgdump /dev/rdisk2 sd-card-backup-2016.03.08.img
To burn it on a card:
imgburn sd-card-backup-2016.03.08.img.xz /dev/rdisk2