Useless use of grep etc.

example.txt

Bad examples:
http://colby.id.au/finding-the-local-ip-address-with-ifconfig-and-sed/
http://www.cyberciti.biz/tips/read-unixlinux-system-ip-address-in-a-shell-script.html

Better:
All except loopback:
ip -o a | awk -F': +| +|/' '$2 != "lo" {print $4}'

Just eth0:
ip -o a | awk -F': +| +|/' '$2 == "eth0" {print $4}'
ip -o addr show dev eth0 | awk -F': +| +|/' '{print $4}'