Shell script to poll a directory and stop upon an event

Shell Programming and Scripting
1

Need shell script to:
1/keep polling a directory "receive_dir" irrespective of having files or no files in it.
2/move the files over to another directory "send_dir".
3/the script should only stop polling upon a file "stopfile" get moved to "receive_dir". Thanks !!

My script:

until [ $i = stopfile ]
 do
   for i in `ls receive_dir`; do
     time=$(date +%m-%d-%Y-%H:%M:%S)
     echo $time
     mv receive_dir/$i send_dir/;
   done
done