Which terminal command to get just IP address and nothing else?

You can write a script that only return the IP like:

/sbin/ifconfig eth0 | grep 'inet addr' | cut -d: -f2 | awk '{print $1}'

For MAC:

ifconfig | grep "inet " | grep -v 127.0.0.1 | cut -d\  -f2

Or for linux system

hostname -i | awk '{print $3}' # Ubuntu 

hostname -i # Debian