netmenu_new_conf

#!/bin/bash
#https://www.opennet.ru/base/sys/sed_edit_interfaces.txt.html

[ -z "$1" ] && echo "iface" && exit 0

interfaces="/etc/network/interfaces"

old_address=$(sed -n -r "/iface $1/!b;:x;n;/^.*address/s/^.*address([ ])*//p;/iface/b;bx" "$interfaces")
old_netmask=$(sed -n -r "/iface $1/!b;:x;n;/^.*netmask/s/^.*netmask([ ])*//p;/iface/b;bx" "$interfaces")
old_gateway=$(sed -n -r "/iface $1/!b;:x;n;/^.*gateway/s/^.*gateway([ ])*//p;/iface/b;bx" "$interfaces")

function ip_prompt() {
while true; do
    read -p "$1: " new_par
    if [ -z `echo $new_par` ]; then
        new_par="$1"
        break
    elif [ -z `echo $new_par | sed -n -r '/((1?[0-9][0-9]?|2[0-4][0-9]|25[0-5])\.){3}(1?[0-9][0-9]?|2[0-4][0-9]|25[0-5])/p'` ]; then
        echo "xxx.xxx.xxx.xxx"
        :
    else
        break
    fi
done
}

echo "Static configuration $1"
echo -n "Enter new address: "
ip_prompt $old_address
new_address=$new_par
clear
echo "Address - $new_address"
echo -n "Enter new netmask: "
ip_prompt $old_netmask
new_netmask=$new_par
clear
echo "Address - $new_address"
echo "Netmask - $new_netmask"
echo -n "Enter new gateway: "
ip_prompt $old_gateway
new_gateway=$new_par
clear
echo "Address - $new_address"
echo "Netmask - $new_netmask"
echo "Gateway - $new_gateway"

echo -n "Enter new DNS1: "
read dns1
echo -n "Enter new DNS2: "
read dns2

clear
echo "Address - $new_address"
echo "Netmask - $new_netmask"
echo "Gateway - $new_gateway"
echo "DNS - $dns1 $dns2"

read -p "Apply changes? [y/n]" apply
if [ "$apply" ] && [ "$apply" == "y" ]; then
    if [[ -z `cat $interfaces | grep $1` ]]; then
        dhclient -r $1
        ip link set dev $1 up
        ip addr add $new_address/$new_netmask dev $1 label $1
        ip route add default via $new_gateway  dev $1 onlink
    else
        sed -i -r "/iface $1/!b;:x;n;s/address.*/address $new_address/;t;/iface/b;bx" $interfaces
        sed -i -r "/iface $1/!b;:x;n;s/netmask.*/netmask $new_netmask/;t;/iface/b;bx" $interfaces
        sed -i -r "/iface $1/!b;:x;n;s/gateway.*/gateway $new_gateway/;t;/iface/b;bx" $interfaces
    fi
    #temporary dns
    if [ "$dns1" ]; then
        echo -e "nameserver $dns1" > /etc/resolv.conf
        if [ "$dns2" ]; then
            echo -e "nameserver $dns2" >> /etc/resolv.conf
        fi
        else echo "" > /etc/resolv.conf
    fi
fi