使用setx的缺点很少，尤其是当您尝试附加到环境变量（例如setx PATH％Path％; C：
mypath）时，这将在每次运行时重复附加到路径中，这可能是一个问题。更糟糕的是，它无法区分机器路径（存储在HKEY_LOCAL_MACHINE中）和用户路径（存储在HKEY_CURRENT_USER中）。您在命令提示符处看到的环境变量由这两个值的串联组成。因此，在调用setx之前：
user PATH == umachine PATH == m%PATH% == m;u> setx PATH %PATH%;newCalling setx sets the USER path by default, hence now:user PATH == m;u;newmachine PATH == m%PATH% == m;m;u;new
每次调用setx追加到PATH时，系统路径都会不可避免地在％PATH％环境变量中重复。这些更改是永久性的，永远不会通过重新启动进行重置，因此会在计算机的整个生命周期内不断累积。
试图在DOS中弥补这一点超出了我的能力范围。所以我转向了Python。我今天想出的解决方案，是通过调整注册表来设置环境变量，包括追加到PATH而不引入重复项，如下所示：
from os import system, environimport win32confrom win32gui import SendMessagefrom _winreg import ( CloseKey, OpenKey, QueryValueEx, SetValueEx, HKEY_CURRENT_USER, HKEY_LOCAL_MACHINE, KEY_ALL_ACCESS, KEY_READ, REG_EXPAND_SZ, REG_SZ)def env_keys(user=True): if user: root = HKEY_CURRENT_USER subkey = 'Environment' else: root = HKEY_LOCAL_MACHINE subkey = r'SYSTEMCurrentControlSetControlSession ManagerEnvironment' return root, subkeydef get_env(name, user=True): root, subkey = env_keys(user) key = OpenKey(root, subkey, 0, KEY_READ) try: value, _ = QueryValueEx(key, name) except WindowsError: return '' return valuedef set_env(name, value): key = OpenKey(HKEY_CURRENT_USER, 'Environment', 0, KEY_ALL_ACCESS) SetValueEx(key, name, 0, REG_EXPAND_SZ, value) CloseKey(key) SendMessage( win32con.HWND_BROADCAST, win32con.WM_SETTINGCHANGE, 0, 'Environment')def remove(paths, value): while value in paths: paths.remove(value)def unique(paths): unique = [] for value in paths: if value not in unique: unique.append(value) return uniquedef prepend_env(name, values): for value in values: paths = get_env(name).split(';') remove(paths, '') paths = unique(paths) remove(paths, value) paths.insert(0, value) set_env(name, ';'.join(paths))def prepend_env_pathext(values): prepend_env('PathExt_User', values) pathext = ';'.join([ get_env('PathExt_User'), get_env('PathExt', user=False) ]) set_env('PathExt', pathext)set_env('Home', '%HomeDrive%%HomePath%')set_env('Docs', '%HomeDrive%%HomePath%docs')set_env('prompt', '$P$_$G$S')prepend_env('Path', [ r'%SystemDrive%cygwinbin', # Add cygwin binaries to path r'%HomeDrive%%HomePath%bin', # shortcuts and 'pass-through' bat files r'%HomeDrive%%HomePath%docsbinmswin', # copies of standalone executables])# allow running of these filetypes without having to type the extensionprepend_env_pathext(['.lnk', '.exe.lnk', '.py'])它不会影响当前进程或父Shell，但会影响运行后打开的所有cmd窗口，而无需重新启动，并且可以安全地进行编辑和重新运行多次，而不会引入任何重复项。
