powershell - 如何在 PowerShell 中找到部分路径的潜在源环境变量？

Question

我想编写一个将常规路径转换为包含环境变量的路径的函数:

例如:

C:\Windows\SomePath

转换成:

%Windir%\SomePath

我将如何做到这一点，这可能吗？

这是我想要做的，但问题是，我需要检查字符串
所有可能的变量，有没有更自动的方法？这样就不需要 -replace 运算符

function Format-Path
{
    param (
        [parameter(Mandatory = $true)]
        [string] $FilePath
    )

    if (![System.String]::IsNullOrEmpty($FilePath))
    {
        # Strip away quotations and ending backslash
        $FilePath = $FilePath.Trim('"')
        $FilePath = $FilePath.TrimEnd('\\')
    }

$FilePath = $FilePath -replace "C:\\Windows", "%Windir%"
$FilePath = $FilePath -replace "C:\\ProgramFiles", "%ProgramFiles%"
$FilePath = $FilePath -replace "C:\\ProgramFiles (x86)", "%ProgramFiles (x86)%"
# ETC.. the list goes on..

return $FilePath
}

# test case
Format-Path '"C:\Windows\SomePath\"'

输出是:

%Windir%\SomePath

编辑:
无效的输入或错误的代码并不是真正的问题，因为最后 $Path可以很容易地检查:

Test-Path -Path ([System.Environment]::ExpandEnvironmentVariables($FilePath))

Answer 1

下面的代码是我对此的看法。路径和反斜杠操作有一些特殊性，所以我试图在评论中解释所有内容。

有一个关键点，那就是 无界字符串搜索，例如由 -replace 执行的搜索, -like , .Contains()等，并可能产生不良结果 当一个变量路径的值是另一个变量路径或目录路径的子字符串时。例如，给定 %ProgramFiles% ( C:\Program Files ) 和 %ProgramFiles(x86)% ( C:\Program Files (x86) )，路径 C:\Program Files (x86)\Test可以转化为%ProgramFiles% (x86)\Test而不是 %ProgramFiles(x86)%\Test如果 %ProgramFiles%碰巧之前测试过%ProgramFiles(x86)% .

解决办法是到仅将变量的路径与完整路径段进行比较 .也就是说，在路径 C:\Program Files (x86)\Test 的情况下，比较会是这样的......

测试与原始路径的相等性 C:\Program Files (x86)\Test .没有变量匹配。

测试与父路径的相等性 C:\Program Files (x86) . %ProgramFiles(x86)%火柴。没有进一步的祖先路径(即 C: )被测试。

%ProgramFiles%永远不会匹配，因为部分路径 C:\Program Files未测试。

通过仅针对完整路径段进行测试，变量与候选路径的比较顺序无关紧要。

New-Variable -Name 'VariablesToSubstitute' -Option Constant -Value @(
    # Hard-code system variables that contain machine-wide paths
    'CommonProgramFiles',
    'CommonProgramFiles(x86)',
    'ComSpec',
    'ProgramData',            # Alternatively: ALLUSERSPROFILE
    'ProgramFiles',
    'ProgramFiles(x86)',
    'SystemDrive'
    'SystemRoot'              # Alternatively: WinDir

    'MyDirectoryWithoutSlash' # Defined below
    'MyDirectoryWithSlash'    # Defined below
);

function Format-Path
{
    param (
        [parameter(Mandatory = $true)]
        [string] $FilePath
    )

    if (![System.String]::IsNullOrEmpty($FilePath))
    {
        # Strip away quotations
        $FilePath = $FilePath.Trim('"')
        # Leave trailing slashes intact so variables with a trailing slash will match
        #$FilePath = $FilePath.TrimEnd('\')
    }

    # Initialize this once, but only after the test code has started
    if ($null -eq $script:pathVariables)
    {
        $script:pathVariables = $VariablesToSubstitute | ForEach-Object -Process {
            $path = [Environment]::GetEnvironmentVariable($_)
            if ($null -eq $path)
            {
                Write-Warning -Message "The environment variable ""$_"" is not defined."
            }
            else
            {
                return [PSCustomObject] @{
                    Name = $_
                    Path = $path
                }
            }
        }
    }

    # Test against $FilePath and its ancestors until a match is found or the path is empty.
    # Only comparing with complete path segments prevents performing partial substitutions
    # (e.g. a path starting with %ProgramFiles(x86)% being substituted with %ProgramFiles%, 
    #       or "C:\Windows.old" being transformed to "%SystemRoot%.old")
    for ($filePathAncestorOrSelf = $FilePath;
        -not [String]::IsNullOrEmpty($filePathAncestorOrSelf);
        # Split-Path -Parent removes the trailing backslash on the result *unless* the result
        # is a drive root.  It'd be easier to normalize all paths without the backslash, but
        # Split-Path throws an error if the input path is a drive letter with no slash, so
        # normalize everything *with* the backslash and strip it off later.
        $filePathAncestorOrSelf = EnsureTrailingBackslash (
            # Protect against the case where $FilePath is a drive letter with no backslash
            # We have to do this here because we want our initial path above to be
            # exactly $FilePath, not (EnsureTrailingBackslash $FilePath).
            Split-Path -Path (EnsureTrailingBackslash $filePathAncestorOrSelf) -Parent
        )
    )
    {
        # Test against $filePathAncestorOrSelf with and without a trailing backslash
        foreach ($candidatePath in $filePathAncestorOrSelf, $filePathAncestorOrSelf.TrimEnd('\'))
        {
            foreach ($variable in $pathVariables)
            {
                if ($candidatePath -ieq $variable.Path)
                {
                    $variableBasePath = "%$($variable.Name)%"
                    # The rest of the path after the variable's path
                    $pathRelativeToVariable = $FilePath.Substring($variable.Path.Length)

                    # Join-Path appends a trailing backslash if the child path is empty - we don't want that
                    if ([String]::IsNullOrEmpty($pathRelativeToVariable))
                    {
                        return $variableBasePath
                    }
                    # Join-Path will join the base and relative path with a slash,
                    # which we don't want if the variable path already ends with a slash
                    elseif ($variable.Path -like '*\')
                    {
                        return $variableBasePath + $pathRelativeToVariable
                    }
                    else
                    {
                        return Join-Path -Path $variableBasePath -ChildPath $pathRelativeToVariable
                    }
                }
            }
        }
    }

    return $FilePath
}

function EnsureTrailingBackslash([String] $path)
{
    return $(
        # Keep an empty path unchanged so the for loop will terminate properly
        if ([String]::IsNullOrEmpty($path) -or $path.EndsWith('\')) {
            $path
        } else {
            "$path\"
        }
    )
}

使用此测试代码...

$Env:MyDirectoryWithoutSlash = 'C:\My Directory'
$Env:MyDirectoryWithSlash    = 'C:\My Directory\'

@'
X:
X:\Windows
X:\Windows\system32
X:\Windows\system32\cmd.exe
X:\Windows.old
X:\Windows.old\system32
X:\Windows.old\system32\cmd.exe
X:\Program Files\Test
X:\Program Files (x86)\Test
X:\Program Files (it's a trap!)\Test
X:\My Directory
X:\My Directory\Test
'@ -split "`r`n?" `
    | ForEach-Object -Process {
        # Test the path with the system drive letter
        $_ -replace 'X:', $Env:SystemDrive

        # Test the path with the non-system drive letter
        $_
    } | ForEach-Object -Process {
        $path = $_.TrimEnd('\')

        # Test the path without a trailing slash
        $path

        # If the path is a directory (determined by the
        # absence of an extension in the last segment)...
        if ([String]::IsNullOrEmpty([System.IO.Path]::GetExtension($path)))
        {
            # Test the path with a trailing slash
            "$path\"
        }
    } | ForEach-Object -Process {
        [PSCustomObject] @{
            InputPath  = $_
            OutputPath = Format-Path $_
        }
    }

......我得到了这个结果......

InputPath                             OutputPath
---------                             ----------
C:                                    %SystemDrive%
C:\                                   %SystemDrive%\
X:                                    X:
X:\                                   X:\
C:\Windows                            %SystemRoot%
C:\Windows\                           %SystemRoot%\
X:\Windows                            X:\Windows
X:\Windows\                           X:\Windows\
C:\Windows\system32                   %SystemRoot%\system32
C:\Windows\system32\                  %SystemRoot%\system32\
X:\Windows\system32                   X:\Windows\system32
X:\Windows\system32\                  X:\Windows\system32\
C:\Windows\system32\cmd.exe           %ComSpec%
X:\Windows\system32\cmd.exe           X:\Windows\system32\cmd.exe
C:\Windows.old                        %SystemDrive%\Windows.old
X:\Windows.old                        X:\Windows.old
C:\Windows.old\system32               %SystemDrive%\Windows.old\system32
C:\Windows.old\system32\              %SystemDrive%\Windows.old\system32\
X:\Windows.old\system32               X:\Windows.old\system32
X:\Windows.old\system32\              X:\Windows.old\system32\
C:\Windows.old\system32\cmd.exe       %SystemDrive%\Windows.old\system32\cmd.exe
X:\Windows.old\system32\cmd.exe       X:\Windows.old\system32\cmd.exe
C:\Program Files\Test                 %ProgramFiles%\Test
C:\Program Files\Test\                %ProgramFiles%\Test\
X:\Program Files\Test                 X:\Program Files\Test
X:\Program Files\Test\                X:\Program Files\Test\
C:\Program Files (x86)\Test           %ProgramFiles(x86)%\Test
C:\Program Files (x86)\Test\          %ProgramFiles(x86)%\Test\
X:\Program Files (x86)\Test           X:\Program Files (x86)\Test
X:\Program Files (x86)\Test\          X:\Program Files (x86)\Test\
C:\Program Files (it's a trap!)\Test  %SystemDrive%\Program Files (it's a trap!)\Test
C:\Program Files (it's a trap!)\Test\ %SystemDrive%\Program Files (it's a trap!)\Test\
X:\Program Files (it's a trap!)\Test  X:\Program Files (it's a trap!)\Test
X:\Program Files (it's a trap!)\Test\ X:\Program Files (it's a trap!)\Test\
C:\My Directory                       %MyDirectoryWithoutSlash%
C:\My Directory\                      %MyDirectoryWithSlash%
X:\My Directory                       X:\My Directory
X:\My Directory\                      X:\My Directory\
C:\My Directory\Test                  %MyDirectoryWithSlash%Test
C:\My Directory\Test\                 %MyDirectoryWithSlash%Test\
X:\My Directory\Test                  X:\My Directory\Test
X:\My Directory\Test\                 X:\My Directory\Test\

请注意，始终首先使用斜杠搜索候选祖先路径，然后不搜索。这意味着在不太可能的情况下，有两个变量路径的区别仅在于尾随斜杠的存在与否，带有尾随斜杠的变量将被匹配。因此，如上所示，C:\My Directory\Test会变成%MyDirectoryWithSlash%Test ，看起来有点奇怪。通过颠倒第一个 foreach 的顺序在函数中循环从...

foreach ($candidatePath in $filePathAncestorOrSelf, $filePathAncestorOrSelf.TrimEnd('\'))

...到...

foreach ($candidatePath in $filePathAncestorOrSelf.TrimEnd('\'), $filePathAncestorOrSelf)

...相关输出更改为...

InputPath                             OutputPath
---------                             ----------
...                                   ...
C:\My Directory\                      %MyDirectoryWithoutSlash%\
...                                   ...
C:\My Directory\Test                  %MyDirectoryWithoutSlash%\Test
C:\My Directory\Test\                 %MyDirectoryWithoutSlash%\Test\
...                                   ...