#!/bin/bash

# ask to set static ip address
read -r -p "Set Static IP address? <y/N> " prompt
if [[ "${prompt,,}" =~ ^(y|yes)$ ]] ; then
    read -r -p "Enter Static IP Address with subnet prefix: " staticip
    read -r -p "Enter Gateway IP Address: " gatewayip
    read -r -p "Enter Primary DNS IP Address: " dnsip1
    # get adapter name
    name=$(basename /sys/class/net/e*)
    # backup original interfaces file
        if [[ ! -f /etc/network/interfaces.bak ]] ; then
            cp /etc/network/interfaces /etc/network/interfaces.bak
        fi
    rm /etc/network/interfaces
    cp /etc/network/interfaces.bak /etc/network/interfaces
    # set static ip
    sed -i "s,^iface $name inet dhcp*,iface $name inet static," /etc/network/interfaces
    echo "        address $staticip" >> /etc/network/interfaces
    echo "        gateway $gatewayip" >> /etc/network/interfaces
    # backup resolv.conf file
        if [[ ! -f /etc/resolv.conf.bak ]] ; then
            cp /etc/resolv.conf /etc/resolv.conf.bak
        fi
    rm /etc/resolv.conf
    # set primary dns ip
    echo "nameserver $dnsip1" >> /etc/resolv.conf
    # ask for secondary dns ip
    read -r -p "Set Secondary DNS IP Address? <y/N> " prompt
        if [[ "${prompt,,}" =~ ^(y|yes)$ ]] ; then
            read -r -p "Enter Secondary DNS IP Address: " dnsip2
            echo "nameserver $dnsip2" >> /etc/resolv.conf
        fi
    # restart the interface
    ifdown $name
    ifup $name
fi