There is a way to find out that public IP using the curl command. If you don't have the package installed, you'll need to install it, as mentioned on ITswapshop, where they explain the process for both Ubuntu:
sudo apt-get install curl
And for openSUSE
sudo zypper install curl
The installation process is similar in other distributions, and once curl is installed, simply type the following in the terminal:
curl ifconfig.me
