Fs_usage runs forever

This keeps gathering data forever, how i can force it to run only for few seconds?

tell application "System Events" to set pid to the unix id of process "Finder" as Unicode text
do shell script "fs_usage -w pid " & pid & " >/Users/Cirno/Desktop/fs_usage.txt" with administrator privileges

How much fs_usage uses cpu/hard disk if i run it all the time to gather all hard disk usage? Or is there better unix tool for this?