Website Monitoring Script

WEBSITE=mywebsite.com
 SUBJECT_DOWN="$WEBSITE DOWN!"
 SUBJECT_UP="$WEBSITE ONLINE"
 EMAILID="an@example.com"
 STRING=$(curl -A "myshell.co.uk - Website Monitoring Script" -s myshell.co.uk | grep -o "myshell.co.uk")
 VALUE="myshell.co.uk"
 LOCKFILE="/tmp/webcheck.lock"

 if [ "$STRING" != "$VALUE" ] && [ ! -f "$LOCKFILE" ]; then
     START_TIME=$(date +%s)
     touch $LOCKFILE
     echo "Website: $WEBSITE is down - $(date)" | mail -s "$SUBJECT_DOWN" $EMAILID
 elif [ "$STRING" = "$VALUE" ] && [ -f "$LOCKFILE" ]; then
     ELAPSED_TIME=$(($(date +%s) - START_TIME))
     rm -f $LOCKFILE
     echo -e "Website: $WEBSITE is back online - $(date)\nDowntime: $ELAPSED_TIME seconds" | mail -s "$SUBJECT_UP" $EMAILID
 fi