Is there a module, a sub, a regular expression or put it simply: a WAY to measure the tempreture outside the room in Perl.

Of course not.
To measure temperature you need a device that's designed for measuring temperature. Something like, oh, a Thermometer for example.
Now if you had an electronic thermometer and you wanted to process the data it produces... well that's a completely different question.

I'm receiving the following error:

Yes, well as they say.. you can't just make stuff up and expect the computer to know what you mean.