Erase a CD-RW or DVD-RW

cdrecord blank=fast

That's the simplest way, but there are more options than just "fast":

all : Blank the entire disk. This may take a long time.
fast : Minimally blank the disk. This results in erasing the PMA, the TOC and the pregap.
track : Blank a track.
unreserve : Unreserve a reserved track.
trtail : Blank the tail of a track.
unclose : Unclose last session.
session : Blank the last session.


Rip a CD or DVD to .iso

dd if=/dev/dvd of=./dvd.iso

Make sure you don't mount the volume first!

Burn an .iso to a disc

wodim -eject -dao speed=2 -v -data mydata.iso

And you can find the capabilities of your drive by:

wodim -prcap dev=/dev/cdrom