Check a webpage everytime in Bash

webchange.bash

#!/bin/bash

me=$(basename $0)
os=$(uname)

function usage
{
	echo
	echo "Usage"
	echo
	echo "--help OR -h: Require help"
	echo "--url OR -u: Set the URL of the page"
	echo "--message OR -m: Set the message to say/echo"
	echo "--update: Update this script"
	echo
	echo "Example of usage: $me -u http://www.google.it -m Changed -s 2"
	echo 
}

function update
{
	echo -n "$me: Downloading update.. "
	sudo curl -s https://raw.github.com/gist/1027721 -o /usr/bin/webchange
	sudo chmod 755 /usr/bin/webchange
	echo "done."
	exit
}

while [ "$1" != "" ]; do
	case $1 in	
		-u | --url )	
			shift
			url="$1"
			;;
        -m | --message )
			shift
			message="$1"
			;;
		-s | --sleep )
			shift
			sleep="$1"
			;;
        -h | --help )
			usage
			exit
			;;
		--update )
			update
			;;
    esac
    shift
done

if [ -z "$url" ]; then
	echo "$me: Url not set"
	usage
	exit
fi

if [ -z "$message" ]; then
	echo "$me: Message not set"
	usage
	exit
fi

if [ -z "$sleep" ]; then
	echo "$me: Sleep not set. Will be set on 0 (may cause high CPU usage)"
	sleep=0
fi

cd /tmp
mkdir $me
cd $me

utime="$(date +%s)"
mkdir $utime
cd $utime

echo -n "$me: Downloading referral page.. "
curl -s --user-agent "Mozilla/4.0" "$url" -o "referral.htm"
echo "done"

echo -n "$me: "

while (true); do
	
	curl -s --user-agent "Mozilla/4.0" -H "Pragma: no-cache" "$url" -o "updated.htm"
	
	if [ -z "$(cmp referral.htm updated.htm)" ]; then 
		
		echo -n "."
		
	else
		
		if [ $os == "Darwin" ]; then
			say "$message"
		elif [ $os = "Linux" ]; then
			espeak "$message"
		fi
		
		echo "$message"
			
	fi
	
	sleep $sleep
	
done