Update a css file from a less file in a loop

lessloop.sh

#!/bin/bash

if [ ! -f "$1" -o ! -f "$2" ]
then
  echo "Run with $0 src.less dest.css"
  exit 1
fi

if [ ${1: -5} != ".less" -o ${2: -4} != ".css" ]
then
  echo "Run with $0 src.less dest.css"
  exit 1
fi

while true
do
  if [ "$1" -nt "$2" ]
  then
    lessc "$1" > "$2"
    echo -n "."
  fi
  sleep 1
done