Ever ran in this situation when you've just added a new repository? W: GPG error: http://ppa.lauchpad.net ubuntu Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 4CF19C3233BAC1B3
Now just execute this script, copy the code next to NO_PUBKEY into your terminal when it asks for it.
Press enter and give your sudo password to get things done.
Pubkey added! :-)
I made this for ubuntu, I don't know if it works on any other linux distributions!