Lots of times you need to determine your public IP address, if you are using Linux operating system to power your PC, you may use some good console commands to guess your public IP address.
wget -q -O - checkip.dyndns.org|sed -e 's/.*Current IP Address: //' -e 's/<.*$/
curl -s checkip.dyndns.org|sed -e 's/.*Current IP Address: //' -e 's/<.*$//'
curl -s http://whatismyip.org/
lynx -dump checkip.dyndns.org
lynx -dump www.whatismyip.com | grep 'Your IP'
As you can see, there are a lot of ways to check your Public IP address using console commands in Linux.
Of course you can always open a browser and enter any of those URIs and check there.