How can I get the new stdout which changes periodically from a process?

[Marc]

I do call a program from my application which changes its stdout 
perdiodically (with ncurses library, I guess), where I'd to get 
somehow "notified" when some change happen (I need to new data 
from that changes and change my application accordingly). 
Currently, I do use spawnProcess() which runs the app in paralel 
but I have no idea how to capture periodically changes in its 
stdout.
It doesn't need to be exact; like a notification for every single 
change. If it checks for changes and report if there's any, every 
say, x seconds is enough.