Powershell“Set-PSDebug -Trace 2”导致意外结果

Question

我遇到了一个奇怪的问题，即在设置“Set-PSDebug -Trace 2”时出现不同的行为。

我将其追溯到一个未正确执行的 switch 语句，并且能够在 Powershell V3 上重现它，但不能在 Powershell V2 或 Powershell V1 上重现（按预期工作）

取如下简单函数：

function DoTest {
$result = "Switch Case Not Executed"
$VendorName = "Microsoft"
switch ($VendorName)
{
    "Microsoft" { $result = "Switch Case Executed" }
}
Write-host "Switch: $($VendorName) -> $result"

}

现在运行以下命令：

#Works as expected
Set-PSDebug -Off; DoTest;

#Doesn't work as expected
Set-PSDebug -Trace 2; DoTest;

带有 PSDebug Trace 的 PosH V3 上的结果

DEBUG:    3+ Set-PSDebug -Trace 2;  >>>> DoTest;
DEBUG:    1+ function DoTest  >>>> {
DEBUG:     ! CALL function 'DoTest'
DEBUG:    2+      >>>> $result = "Switch Case Not Executed"
DEBUG:     ! SET $result = 'Switch Case Not Executed'.
DEBUG:    3+      >>>> $VendorName = "Microsoft"
DEBUG:     ! SET $VendorName = 'Microsoft'.
DEBUG:     ! SET $switch = 'Microsoft'.
DEBUG:    4+     switch ( >>>> $VendorName)
DEBUG:     ! SET $switch = ''.
DEBUG:    9+      >>>> Write-host "Switch: $($VendorName) -> $result"
DEBUG:    9+     Write-host "Switch: $( >>>> $VendorName) -> $result"
Switch: Microsoft -> Switch Case Not Executed
DEBUG:   11+  >>>> }

在 PoSH 版本 3 中，即使是调试跟踪也表明该值已设置，但似乎完全跳过了 switch 语句。我什至尝试了Set-StrictMode，一切运行良好。只有当我启用 PSDebug 跟踪时。这种行为是有意的吗？

Answer 1

经过详尽调查，这似乎是 Powershell 中的一个错误。 $switch 变量在调试模式下被破坏，最终成为某种数组枚举器，在一个空数组或类似的东西上。我建议在http://connect.microsoft.com 上提交问题

解决方法 1：

# Pro: No scoping differences between if statement blocks and function
# Con: big piles of If ... else if ... else if ... can get really annoying to code and maintain
# Con: Statements are limited to single execution, pipeline is lifted to function level instead of statement level
... same code as before but using an if instead of switch ...
if($VendorName = 'Microsoft') { $result = "Switch Case Executed" }
else { $result = "FAIL!" }

解决方法 2：

# Pro: Each script block is self-contained and has private scope
# Pro: "cases" can be added without modifying DoIt function, and even passed into the function 
# Pro: "cases" can be used in a pipeline
# Con: Indirect script blocks can be difficult to understand at first
function DoTest {
    $result = "Switch Case Not Executed"
    $VendorName = "Microsoft"

    $SwitchHack = @{
        Microsoft = { "Microsoft Case Executed" }
        Default = { "Default Case Executed" }
    }

    if($SwitchHack.Keys -contains $VendorName) {
        $result = $SwitchHack."$VendorName".InvokeReturnAsIs()
    } else {
        $result = $SwitchHack.Default.InvokeReturnAsIs()
    }

    'Switch: {0} -> {1}' -f $VendorName, $result | Write-Host 
}

Set-PSDebug -Trace 2
DoTest

因为我很无聊，所以我写了 Workaround 3，它只有 2 个，将 Switch 移到一个函数中

function Switch-Object {
    param(
        [Parameter(Mandatory=$true)]
            [String]$In,
        [Parameter(Mandatory=$true)]
            [hashtable]$Actions
    )

    try {
        $Actions."$In".InvokeReturnAsIs()
    } 
    catch {
        throw "Unknown Action Label"
    }
}

function DoTest {
    $result = "Switch Case Not Executed"
    $VendorName = "Microsoft"

    $VendorActions = @{
        Microsoft = { "Microsoft Case Executed" }
    }

    $result = Switch-Object -On:$VendorName -Actions:$VendorActions
    'Switch: {0} -> {1}' -f $VendorName, $result | Write-Host 
}

Set-PSDebug -Trace 2
DoTest