tail -f /root/var/log/ocmp/ocmpclient.log | grep 'File Detected\|File Sending\|File Recieved\|Disconnecting'

I am using the above command now i want to write the output of this to go to a file output.txt
so i modified it as
#!/bin/sh
while true
do
tail -f /root/var/log/ocmp/ocmpclient.log | grep 'File Detected\|File Sending\|File Recieved\|Disconnecting' > output.txt
done


Now the problem is the file is created but doesnt contain anything.