#!/bin/bash

ivp4_pattern='/^([0-9]{1,3}.){3}[0-9]{1,3}(/([0-9]|[1-2][0-9]|3[0-2]))?$/igm'
networks=$(ip addr | grep "inet" | awk '{print $2}')

while read -r line;
do
    echo "$line"
done <<< "$networks"

echo "$ivp4_pattern"
echo "$networks" | grep "$ivp4_pattern"

[jonathan@localhost ~]$ ./script.sh
127.0.0.1/8
::1/128
172.16.155.128/24
fe80::da84:977a:d654:7716/64
/^([0-9]{1,3}.){3}[0-9]{1,3}(/([0-9]|[1-2][0-9]|3[0-2]))?$/igm