How can I fetch the ethernet port given the ip address?

Question

I am trying to write a bash script to fetch the ethernet port of an interface whose IP address I know. I need to grab this from ifconfig but can't seem to be able to figure out how to go about it. Any ideas?

Thanks.

Answer 1

Replace 127.0.0.1 with the ip address you want to get the interface info for

ifconfig  | grep 127.0.0.1 -B1 | grep Link | cut -f 1 '-d '

If you also want to identify the physical port on the machine, run

ethtool -p $OUTPUT_OF_FIRST_COMMAND

It will blink the light on the ethernet card associated with that interface

Answer 2

A little messy but should work:

/sbin/ifconfig | grep -B1 1.2.3.4 | awk '{print $1; exit}'

Optionally, you could use the ip command which, when used with the -o|-oneline option, is a lot easier to parse. For example

ip -o addr | awk '/1.2.3.4/{print $2}'