shell script if output equal any ip address

Question

If $IP output equal to any ip address must print 1, else must print 0.

#!/bin/sh

IP=$(/usr/local/bin/dig ns.ripe.net. a +short)

if [ $IP = "[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}" ]; then
   echo 1
elif [ $IP != $ANY_IP ]; then
   echo 0
fi

I need write script,which must check if "/usr/local/bin/dig ns.ripe.net. a +short" output return any ip address,should return 1,else return 0. The purpose of this script is to check dnssec. How can I denote any ip address for comparing?

Answer 1

In increasing order of accuracy:

1. POSIX shell

   case $IP in 
       *.*.*.*) echo "$IP contains at least 3 dots" ;;
       *) echo "$IP does not contain 3 dots" ;;
   esac
   

2. bash

   shopt -s extglob
   if [[ $IP == +([0-9]).+([0-9]).+([0-9]).+([0-9]) ]]; then
       echo "$IP contains digits separated by dots
   fi
   

3. bash

   looks_like_IP_address() {
      [[ $1 =~ ^([0-9]+)"."([0-9]+)"."([0-9]+)"."([0-9]+)$ ]] &&
      (( 0 <= ${BASH_REMATCH[1]} && ${BASH_REMATCH[1]} <= 255 )) &&
      (( 0 <= ${BASH_REMATCH[2]} && ${BASH_REMATCH[2]} <= 255 )) &&
      (( 0 <= ${BASH_REMATCH[3]} && ${BASH_REMATCH[3]} <= 255 )) &&
      (( 0 <= ${BASH_REMATCH[4]} && ${BASH_REMATCH[4]} <= 255 ))
   }
   if looks_like_IP_address "$IP"; then
       echo "$IP looks like an IP address"
   fi