Alert when a certificate is under thirty days

end=$(echo | openssl s_client -servername "$1" -connect "$1:443" 2>/dev/null 
      | openssl x509 -noout -enddate | cut -d= -f2)
days=$(( ($(date -d "$end" +%s) - $(date +%s)) / 86400 ))
[ "$days" -lt 30 ] && echo "WARN $1 expires in $days days"