If a DHCP interface fails to get an IP address, deleting the interface results in a bash script error.
STEPS TO REPRODUCE
- Start a Vyos ISO on a LAN with no DHCP server
- Run the following commands:
configure set interfaces ethernet eth0 address dhcp commit delete interfaces ethernet commit
[ interfaces ethernet eth0 address dhcp ] Usage: grep [OPTION]... PATTERN [FILE]... Try 'grep --help' for more information 
This is caused by the vyatta-address script in vyatta-cfg-system assuming it will always get an address out of a "ip address show".