Sometimes, you want to see whether a certain network interface is really connected to a particular cable.
With the following command you can issue a “rapid” ping, which will issue ping after ping – immediate stop after disconnecting the LAN cable.
Assuming that you want to test a USB Ethernet adapter (device eth1):
ping -I eth1 192.168.1.1 -A
replace 192.168.1.1 with an appropriate ping host of your choice. That is a capital “i” in there, for interface.
This also makes an impressive “computer is working” kind of terminal background to impress friends “not in the know” 