Shell script question: continuous tail -f processing?

Question

bash

Greetings!
I want something strange...
Let's say I have numbers falling into a certain file:
1
2
3
4
I want to continuously, as new lines arrive, calculate their average. Those. to display
1
1.5
2,
2.5
At the same time, I do not want to check the file periodically, but I want that as soon as a new line appears, the value will immediately appear. Those. as tail -fsoon as with additional logic.

Answer 1

Our problem. I cheated a little, the line I called was:
tail -f file.txt | awk '{..morestuff..; printf result;}' | awk '{total+=$0;count+=1;print total/count}'
It does not work because the first awk buffers the output and does not give it to the second. Therefore, it is right to do:
tail -f file.txt | awk '{..morestuff..; printf result; fflush()}' | awk '{total+=$0;count+=1;print total/count}'

Answer 2

Something I don’t stick in, what kind of average do you think if your third number is 3, and the fourth is 3.5.