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，因此我尝试在注释中解释所有内容。
有一个关键要点就是无限制的字符串搜索，例如由-replace, -like, .Contains()等，并可能产生不良结果当一个变量的路径的值是另一个变量的路径或目录的路径的子字符串时。例如，给定%ProgramFiles% (C:\Program Files) and %ProgramFiles(x86)% (C:\Program Files (x86)）， 路径C:\Program Files (x86)\Test可以转化为%ProgramFiles% (x86)\Test代替%ProgramFiles(x86)%\Test if %ProgramFiles%恰好之前测试过%ProgramFiles(x86)%.
解决办法是仅将变量的路径与完整路径段进行比较。也就是说，在路径的情况下C:\Program Files (x86)\Test，比较会像这样......
- 测试与原始路径是否相等
C:\Program Files (x86)\Test。没有变量匹配。
- 测试与父路径是否相等
C:\Program Files (x86). %ProgramFiles(x86)%火柴。没有进一步的祖先路径（即C:）进行测试。
-
%ProgramFiles%永远不会匹配，因为部分路径C:\Program Files没有经过测试。
通过仅针对完整路径段进行测试，变量与候选路径进行比较的顺序并不重要。
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，候选祖先路径始终首先搜索带有尾部斜杠的搜索，然后搜索不带尾部斜杠的路径。这意味着，在不太可能发生的情况下，存在两个变量路径，其区别仅在于是否存在尾部斜杠，具有尾部斜杠的变量将被匹配。因此，如上所示，C:\My Directory\Test会变成%MyDirectoryWithSlash%Test，这看起来有点奇怪。通过颠倒第一个的顺序foreach在函数中循环...
foreach ($candidatePath in $filePathAncestorOrSelf, $filePathAncestorOrSelf.TrimEnd('\'))
...to...
foreach ($candidatePath in $filePathAncestorOrSelf.TrimEnd('\'), $filePathAncestorOrSelf)
...相关输出更改为此...
InputPath OutputPath
--------- ----------
... ...
C:\My Directory\ %MyDirectoryWithoutSlash%\
... ...
C:\My Directory\Test %MyDirectoryWithoutSlash%\Test
C:\My Directory\Test\ %MyDirectoryWithoutSlash%\Test\
... ...
