Any script with a 'for' loop doesn't produce any output

[asgharam]

I wrote a bash script but i3blocks wouldn't show the output of the script at all. after hours of tinkering this and that, I found out any bash script that had a 'for' loop wouldn't work in i3blocks. Like a script with the content bellow wouldn't show any output on the bar:

#!/bin/bash
for ((i=0; i<100; i++)); do echo $i; sleep 1; done

The interval for the script block in i3blocks's config is set to 1.
What is the problem?