powershell - 如何在不扩展 token 的情况下获取 PATH 环境变量的值？

Question

我正在编写一个 PowerShell 脚本，将文件夹名称转换为 PATH 环境变量中的短名称并保存更改。它适用于显式路径，但它会扩展标记，因此当我保存更改时，标记会替换为显式路径。我想保留 token 。

例如，如果我的 PATH 是这样的:%SystemRoot%;%SystemRoot%\system32;C:\Program Files\TortoiseSVN\bin;C:\ProgramData\chocolatey\bin
我想要这个结果:%SystemRoot%;%SystemRoot%\system32;C:\PROGRA~1\TORTOI~1\bin;C:\PROGRA~3\CHOCOL~1\bin
但是我得到了这个:C:\Windows;C:\Windows\system32;C:\PROGRA~1\TORTOI~1\bin;C:\PROGRA~3\CHOCOL~1\bin
这是说明问题的完整脚本。

# get the current path.
# I ended up not using either of these approaches because they appear to
# be contextual; on my system, at least, they include paths that aren't
# seen when I view the PATH value from the System Properties -> Environment
# Variables dialog box.
$current_path = $env:Path
$current_path = [System.Environment]::GetEnvironmentVariable("Path")

# Instead, I get the PATH value directly from the registry, like so:
$current_path = (Get-ItemProperty -Path 'HKLM:\SYSTEM\CurrentControlSet\Control\Session Manager\Environment' -Name Path).Path

# The problem is that PowerShell expands the tokens even when reading from the 
# registry, so I can't detect the tokens and ignore them.  What I really want
# is just the literal string value, with no token evaluation.
# Here's a sample value; this is what I see in regedt32 and the system dialogs,
# but it's not what I get from the line above.
$current_path = '%SystemRoot%;%SystemRoot%\system32;C:\Program Files\TortoiseSVN\bin;C:\ProgramData\chocolatey\bin'

$new_path = ''

# the FileSystemObject has a method to convert the path using short names for the folders.
$fso = New-Object -ComObject Scripting.FileSystemObject

# Individual paths are delimited by a semicolon.  Skip paths with tokens, 
# and preserve trailing slashes in each path.
$current_path.Split(';') |
    ForEach-Object { 
        if ($_.StartsWith('%'))
            { $_ }
        elseif ($_.EndsWith('\'))
            { "$($fso.GetFolder($_).ShortPath)\" }
        else
            { "$($fso.GetFolder($_).ShortPath)" } 
    } |
    ForEach-Object { $new_path += "$_;" }

# remove the extra semicolon from the end the new PATH.
$new_path = $new_path.TrimEnd(";")

"Current PATH length: $($current_path.Length)"
"New PATH length: $($new_path.Length)"

$new_path

# commented out so you don't accidentally update your path if you try out this script
#[System.Environment]::SetEnvironmentVariable("Path", $new_path, "Machine")

如果我可以从注册表中获取文字字符串值似乎应该很容易，但到目前为止我还没有弄清楚如何做到这一点。

Answer 1

这不是 PowerShell 本身，而是底层 Windows 注册表的“功能”。 Path 变量的类型为 REG_EXPAND_SZ，它会在检索时自动扩展环境变量。我认为您无法使用内置 cmdlet 来解决它，但您可以使用 .NET Microsoft.Win32.Registry API。使用 RegistryKey.GetValue 重载和 RegistryValueOptions.DoNotExpandEnvironmentNames :

$regKey = [Microsoft.Win32.Registry]::LocalMachine.OpenSubKey('SYSTEM\CurrentControlSet\Control\Session Manager\Environment', $true)
$regKey.GetValue('Path', $null, "DoNotExpandEnvironmentNames")

当需要保存变量时，使用 SetValue 和 RegistryValueKind.ExpandString 的重载以正确的类型保存它:

$regKey.SetValue("Path", $new_path, "ExpandString")