Check for IP validity

Question

How do I check the validity of an IP address in a shell script, that is within the range 0.0.0.0 to 255.255.255.255?

Answer 1

In the most simple form:-

#!/bin/bash
while true;
do
read -p "Enter a ip: " IP
echo "${IP}" > ip.txt
OCT1=$(cat ip.txt | awk -F "." '{print $1}')
OCT2=$(cat ip.txt | awk -F "." '{print $2}')
OCT3=$(cat ip.txt | awk -F "." '{print $3}')
OCT4=$(cat ip.txt | awk -F "." '{print $4}')
REGEX_IP='^[0-9]{1,3}[.][0-9]{1,3}[.][0-9]{1,3}[.][0-9]{1,3}$'
if [[ ${IP} =~ ${REGEX_IP} ]]
then
    if [[ ${OCT1} -gt 255 || ${OCT2} -gt 255 || ${OCT3} -gt 255 || ${OCT4} -gt 255 ]]
        then
        echo "Please enter a valid ip"
        continue
        fi

break
else
        echo "Please enter a valid ip"
        continue
fi
done

This will cover all the scenarios.