1
直接System.Environment.GetEnvironmentVariable["变量名"];
比如得到计算机名、程序文件夹等
[sourcecode language='c#']
TextBox1.Text = System.Environment.GetEnvironmentVariable(“COMPUTERNAME”) +”rn”;
TextBox1.Text = System.Environment.GetEnvironmentVariable(“ProgramFiles”) +”rn”;
[/sourcecode]

至于像“桌面”“我的文档”可以这么得到

[code language='C#']
TextBox1.Text += Environment.GetFolderPath(Environment.SpecialFolder.Personal)+ "rn";//我的文档
TextBox1.Text += Environment.GetFolderPath(Environment.SpecialFolder.Desktop) + "rn";//桌面
[/code]
就是用Environment.GetFolderPath(Environment.SpecialFolder.特殊文件夹)
像cookies、音乐、视频、发送到等等都可以这样获得路径

2

3

C#读取设置path环境变量并重启计算机

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using Microsoft.Win32;//注册表操作要引用的空间
using System.Runtime.InteropServices;//调用API函数需要的引用，来加载非托管类user32.dll

namespace 用程序修改环境变量
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {

        }
        /// <summary>
        /// 读取注册表
        /// path的路径：[HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\Session Manager\Environment]
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        private void tbnRead_Click(object sender, EventArgs e)
        {
            RegistryKey regLocalMachine = Registry.LocalMachine;
            RegistryKey regSYSTEM = regLocalMachine.OpenSubKey("SYSTEM", true);//打开HKEY_LOCAL_MACHINE下的SYSTEM
            RegistryKey regControlSet001 = regSYSTEM.OpenSubKey("ControlSet001", true);//打开ControlSet001
            RegistryKey regControl = regControlSet001.OpenSubKey("Control", true);//打开Control
            RegistryKey regManager = regControl.OpenSubKey("Session Manager", true);//打开Control

            RegistryKey regEnvironment = regManager.OpenSubKey("Environment", true);//打开MSSQLServer下的MSSQLServer
            this.richTextBox1.Text = regEnvironment.GetValue("path").ToString();//读取path的值
        }

        private void btnClose_Click(object sender, EventArgs e)
        {
            Close();
        }

        /// <summary>
        ///
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="e"></param>
        [DllImport("user32.dll", SetLastError = true, CharSet = CharSet.Auto)]//SendMessageTimeout是在user32.dll中定义的
        public static extern IntPtr SendMessageTimeout(
     IntPtr windowHandle,
     uint Msg,
     IntPtr wParam,
     IntPtr lParam,
     SendMessageTimeoutFlags flags,
     uint timeout,
     out IntPtr result
     );

        [Flags]
        public enum SendMessageTimeoutFlags : uint
        {
            SMTO_NORMAL = 0x0000,
            SMTO_BLOCK = 0x0001,
            SMTO_ABORTIFHUNG = 0x0002,
            SMTO_NOTIMEOUTIFNOTHUNG = 0x0008
        }

        private void btnWrite_Click(object sender, EventArgs e)
        {

            RegistryKey regLocalMachine = Registry.LocalMachine;
            RegistryKey regSYSTEM = regLocalMachine.OpenSubKey("SYSTEM", true);//打开HKEY_LOCAL_MACHINE下的SYSTEM
            RegistryKey regControlSet001 = regSYSTEM.OpenSubKey("ControlSet001", true);//打开ControlSet001
            RegistryKey regControl = regControlSet001.OpenSubKey("Control", true);//打开Control
            RegistryKey regManager = regControl.OpenSubKey("Session Manager", true);//打开Control

            RegistryKey regEnvironment = regManager.OpenSubKey("Environment", true);//打开MSSQLServer下的MSSQLServer
            regEnvironment.SetValue("path", this.richTextBox1.Text);//读取path的值

            MessageBox.Show("修改成功");
            //下面利用发送系统消息，就不要重新启动计算机了
           const int HWND_BROADCAST=0xffff;
           // DWORD dwMsgResult = 0L;
           const uint WM_SETTINGCHANGE = 0;
           const long SMTO_ABORTIFHUNG = 0x2;
          System.UInt32 dwMsgResult1=0;
          long s;
         // SendMessageTimeout(HWND_BROADCAST, WM_SETTINGCHANGE, 0, (string)"Environment", SMTO_ABORTIFHUNG, 5000,(long)s);

        }
        /// <summary>
        /// 重新启动计算机
        /// </summary>
        /// <param name="x"></param>
        /// <param name="y"></param>
        /// <returns></returns>
        [DllImport("user32.dll")]
        //主要ＡＰＩ是这个，注意：必须声明为static extern
        private static extern int ExitWindowsEx(int x, int y);
        private void button1_Click(object sender, EventArgs e)
        {
            ExitWindowsEx(2,0);
        }
    }
}