o1='1[0-9]{0,2}|2([6-9]|[0-4][0-9]?|5[0-4]?)?|[3-9][0-9]?'
o0='0|255|'"$o1"
if echo "$ip" | egrep -v "^($o1)(\.($o0)){2}\.($o1)$" >/dev/null; then
  echo invalid ip
fi