Well, checking when your directories and files change should be a job for some inotify based tool, not periodically launched ls, sadly, inotify based version of common unix utilities are still very optional and hackish, not found in the base distro.
Fast-forwarding to now, having just installed inotify-tools (Debian/Ubuntu package):
while true; do inotifywait . &> /dev/null ; ls ; done
atchange . ls
while true; do inotifywait -qq -e modify [filename]; [command]; done
function atchange(){
while true;
do inotifywait -qq -e modify $1;
$2;
done if which inotifywait > /dev/null ; then
function atchange(){
FILE="$1"
shift
while inotifywait -qq -e modify -e attrib "$FILE"; do
"$@";
done;}
fi
EDIT changed the "while true" so that the function stops on an error rather than infinitely looping when something goes wrong, like FILE ceasing to exist. A file temporarily disappearing would scupper the script though, whereas the perl script deals quietly with that.