Either way, it would be an interesting match, as I don't remember seeing them play against each other in a World Cup.
You've never seen them at the World Cup or on any other occasion, because there really hasn't been a game between them yet.
By the way, I'm lying, there was actually a friendly game in 2014, which Portugal won 1-0, in the last minute of the game.
But in official games, they never faced each other.