C# code to read a binary DD-WRT backup file and export commands to set the values on the router

ddwrt_nvram.cs

// read a DD-WRT nvrambak_xyz.bin backup file and create "nvram set" commands FOR COMPARISON ONLY
// NOTE: some values may have issues, so you can't just copy and paste the whole output or it can mess up your router
// The format should be similar to processes to export from the router via the command line:
// https://gist.github.com/Aikhjarto/5b1c6b5e5d373d8d60c004e075b29acc
// https://gist.github.com/rambotech/d1e2486228c5e972c3c9c8936920f2fc
var set = new List<string>();
using var file = System.IO.File.OpenRead(args[0]);
var buffer = new byte[0xFFFF];
int len = 6;
int count = file.Read(buffer, 0, len);
if (count != len || System.Text.Encoding.ASCII.GetString(buffer, 0, count) != "DD-WRT") throw new InvalidDataException("unrecognized format");
len = (file.ReadByte() | file.ReadByte() << 8);
while (-1 != (len = file.ReadByte()))
{
    count = file.Read(buffer, 0, len);
    if (count != len) throw new InvalidDataException("unexpected end of name");
    var name = System.Text.Encoding.ASCII.GetString(buffer, 0, count);
    len = (file.ReadByte() | file.ReadByte() << 8);
    if (len > 0)
    {
        count = file.Read(buffer, 0, len);
        if (count != len) throw new InvalidDataException("unexpected end of value");
        var value = System.Text.Encoding.ASCII.GetString(buffer, 0, count);
        set.Add($"nvram set {name}='{value.Replace("'", "\\'")}'");
    }
}
set.Sort();
foreach (var cmd in set) Console.WriteLine(cmd);

Project file to use dotnet run:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net7.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
  </PropertyGroup>
</Project>