How to know public IP and public DNS Name of the VM direcly from the VM itself ?

Hello

I'm preparing a VM with my own application to deploy it into the VMdepot. When the user will start the VM I need to update some file of my application using a SH script at startup. 

I need to find a way to retreive the Public IP and the Public Host Name directly from the VM itself (just like if I was using a shell). The OS VM is Ubuntu.

Does someone know how to achieve that ?

Thank you