#!/usr/bin/bash

# assumes only two NET: entries and toggles with comments

toggle() {
  in_net=""
  current_net=""

  while read -r line; do

    # net
    if [[ $line =~ ^#\ *NET: ]];then
      current_net=${line#*:}
      in_net=y
      echo "$line"
      continue
    fi

    # end net
    if [[ -n $in_net && $line =~ ^\ *$ ]]; then
      in_net=""
      current_net=""
      echo "$line"
      continue
    fi

    # if in net and disabled, enable
    if [[ -n $in_net && $line =~ ^# ]]; then
      echo "${line##\#}"
      continue
    fi

    # if in net and enabled, disable
    if [[ -n $in_net && ! $line =~ ^# ]]; then
      echo "#${line}"
      continue
    fi

    echo "$line"

  done < /etc/resolv.conf
}

tmpfile=$(mktemp)
toggle >| "$tmpfile"
sudo cp "$tmpfile" /etc/resolv.conf