powershell - 什么时候 ScriptBlock 不是 ScriptBlock？

Question

我并不是要让这个问题听起来太可爱，但这确实是眼前的问题。考虑安装在 $env:PSModulePath 下的 PowerShell 模块 Test.psm1 中定义的以下两个函数:

function Start-TestAsync
{
    [CmdletBinding()]
    param([ScriptBlock]$Block, [string]$Name = '')   
    Start-Job { Start-Test -Name $using:Name -Block $using:Block }
}

function Start-Test
{
    [CmdletBinding()]
    param([ScriptBlock]$Block, [string]$Name = '')
    # do some work here, including this:
    Invoke-Command -ScriptBlock $Block
}

导入模块后，我可以运行同步功能...

PS> Start-Test -Name "My Test" -Block { ps | select -first 9 }

...并显示 Get-Process 的适当输出。

但是，当我尝试运行异步版本时...

PS> $testJob=Start-TestAsync -Name "My Test" -Block { ps | select -first 9 }

...然后查看其输出...

PS> Receive-Job $testJob

...它无法将参数引入 Start-Test 函数，报告它无法将 String 转换为 ScriptBlock。因此，-Block $using:Block 传递的是字符串而不是 ScriptBlock!

经过一些实验，我确实找到了解决方法。如果我修改 Start-Test，使 $Block 参数的类型为 [string] 而不是 [ScriptBlock] —— 然后将该字符串转换回 block 以提供给 Invoke-Command...

function Start-Test
{
    [CmdletBinding()]
    param([string]$Block, [string]$Name = '')
    $myBlock = [ScriptBlock]::Create($Block)
    Invoke-Command -ScriptBlock $myBlock
}

当我从上面运行相同的命令时，我得到了正确的结果:

PS> $testJob=Start-TestAsync -Name "My Test" -Block { ps | select -first 9 }
PS> Receive-Job $testJob

using 范围在我的初始示例中是否正常工作(将 ScriptBlock 转换为字符串)？关于它的有限文档(about_Remote_Variables，about_Scopes)提供的指导很少。最后，当 Start-Test 的 $Block 参数被键入为 [ScriptBlock] 时，有没有办法让 Start-Test 工作？

Answer 1

这显然是设计使然:https://connect.microsoft.com/PowerShell/feedback/details/685749/passing-scriptblocks-to-the-job-as-an-argument-cannot-process-argument-transformation-on-parameter

解决方法(来自上面的链接)是使用[ScriptBlock]::Create():

This happens because the $ScriptToNest scriptblock is getting converted into a string because of how PowerShell serialization works. You can work around this by explicitly creating the scriptblock. Replace the param() block in your $OuterScriptblock with the following ($ip is the input):

[scriptblock]$OuterScriptblock = {
param($ip)
[ScriptBlock]$ScriptToRun = [ScriptBlock]::Create($ip)

这将是您的解决方法(如您所见):

function Start-TestAsync
{
    [CmdletBinding()]
    param([ScriptBlock]$Block, [string]$Name = '')
    Start-Job { Start-Test -Name $using:Name -Block $using:Block }
}

function Start-Test
{
    [CmdletBinding()]
    param($Block, [string]$Name = '')
    # do some work here, including this:
    $sb = [ScriptBlock]::Create($Block)
    Invoke-Command -ScriptBlock $sb
}