List VMs and their state

VBoxManage list vms -l | grep -e ^Name: -e ^State  | sed "s/Name:[ ]*\(.*\)/\1 \//;s/State:[\ ]*//" | paste -d " " - -

Start VM in headless mode

VBoxManage startvm <vm> --type headless

Stop VM (clean)

VBoxManage controlvm <vm> acpipowerbutton

Stop VM (force power off)

VBoxManage controlvm <vm> poweroff