Getting IP adress nic

#!/usr/bin/env bash
set -euo pipefail

_ip_notfound() {
    clear
    sleep 1
    echo "Erro, IP não encontrado."
    exit 1
}

_show_dev() {
    ip address show dev eth0
}

_address_condition() {
    _show_dev > /dev/null 2>&1
}

_ipv4() {
    if _address_condition; then
        _show_dev |
        grep -E '\w{3}[.]' |
        awk '{print $2}'
    else
        _ip_notfound
    fi
}

_ipv6() {
    if _address_condition; then
        _show_dev |
        grep -E 'inet6\s[0-9a-fA-F]{4}[:]' |
        awk '{print $2}'
    else
        _ip_notfound
    fi
}

case $1 in
    4)  _ipv4;;
    6)  _ipv6;;
    *)  clear; echo "Não existe essa versão de IP, digite 4 ou 6"
esac