SetMPath.cs

using Microsoft.Win32;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SetMPath
{
    internal class Program
    {
        static int Main(string[] args)
        {
            if (args.Length == 0)
            {
                Console.WriteLine(@"No args !");
                return -1;
            }
            if (args[0] != "prepend" && args[0] != "append" && args[0] != "replace")
            {
                Console.WriteLine(@"Wrong action !");
                return -1;
            }
            string file = System.IO.Path.GetDirectoryName(System.Reflection.Assembly.GetExecutingAssembly().Location);
            file += @"\reg.txt";
            if(!System.IO.File.Exists(file))
            {
                Console.WriteLine(@"No reg file !");
                return -1;
            }
            string line = System.IO.File.ReadAllLines(file)[0];
            if(line == "")
            {
                Console.WriteLine(@"Reg file empty !");
                return -1;
            }
            string SysKey = @"SYSTEM\CurrentControlSet\Control\Session Manager\Environment";
            string orig = (string)Registry.LocalMachine.CreateSubKey(SysKey).GetValue(@"PATH","",RegistryValueOptions.DoNotExpandEnvironmentNames);
            if(orig == "" )
            {
                Console.WriteLine(@"Cannot get original content !");
                return -1;
            }
            string final;
            switch (args[0]){
                case "replace":
                    Registry.LocalMachine.CreateSubKey(SysKey).SetValue(@"PATH", line, RegistryValueKind.ExpandString);
                    return 0;
                case "prepend":
                    if (!line.EndsWith(@";"))
                        line += @";";
                    final = line + orig;
                    Registry.LocalMachine.CreateSubKey(SysKey).SetValue(@"PATH", final, RegistryValueKind.ExpandString);
                    return 0;
                case "append":
                    if (line.EndsWith(@";"))
                        line = line.Remove(line.Length - 1, 1);
                    if (!orig.EndsWith(@";"))
                        orig += @";";
                    final = orig + line;
                    Registry.LocalMachine.CreateSubKey(SysKey).SetValue(@"PATH", final, RegistryValueKind.ExpandString);
                    return 0;
            }
            return -2;
        }
    }
}