Powershell：如何重復條件直到傳遞有效值？

我正在撰寫一個將目錄結構（不包括檔案）克隆到新目錄的腳本。到目前為止，這是我的代碼：

Function Copy-DirectoryStructure{
    [CmdletBinding()]

    Param(
        [Parameter(Mandatory=$true,ValueFromPipeline=$true)] 
        [string]$Path
    )

    # Test whether the path is exactly a drive letter
    if($Path -match '^[a-zA-Z]:\\$' -or $Path -match '^[a-zA-Z]:$'){
        throw "Path cannot be at the root of a drive. Aborting."
    }

    # Check if the path is valid
    if(Test-Path -Path $Path -PathType Container){
        # Create the destination path format
        $DestinationPath = (get-item $Path).FullName   ' Folder Copy'
        # Test if our destination already exists.
        # If so, prompt for a new name
        if(Test-Path -Path $DestinationPath -PathType Container){
            Write-Warning "The destination path already exists."
            $NewFolderName = Read-Host -Prompt "Input the name of the new folder to be created."
            $DestinationPath = (get-item $Path).parent.FullName   '\'   $NewFolderName
        }
        # Begin copy
        robocopy $Path $DestinationPath /e /xf *.* | Out-Null
    } else {
        throw "Invalid directory was passed. Aborting."
    }
}

Copy-DirectoryStructure -Path "C:\Users\[username]\Desktop\Test"

相關部分在這里：

# Create the destination path format
        $DestinationPath = (get-item $Path).FullName   ' Folder Copy'
        # Test if our destination already exists.
        # If so, prompt for a new name
        if(Test-Path -Path $DestinationPath -PathType Container){
            Write-Warning "The destination path already exists."
            $NewFolderName = Read-Host -Prompt "Input the name of the new folder to be created."
            $DestinationPath = (get-item $Path).parent.FullName   '\'   $NewFolderName
        }

現在，如果 $DestinationPath 已經存在，它會提示用戶輸入一個新名稱，然后繼續執行 robocopy。但是，如果用戶輸入的檔案夾名稱也已經評估為現有路徑，該怎么辦？

我想優雅地處理這種情況并重新提示輸入新路徑，直到用戶輸入尚不存在的目標路徑。

我不知道該怎么做。

我知道這是一個極端的極端情況，但我想讓我的代碼盡可能安全。

任何幫助是極大的贊賞。

uj5u.com熱心網友回復：

從函式中完全洗掉互動式位 - 它應該只是在目標路徑存在時失敗 - 而是為用戶提供一種顯式傳遞替代目標路徑的方法：

Function Copy-DirectoryStructure{
    [CmdletBinding()]

    Param(
        [Parameter(Mandatory=$true,ValueFromPipeline=$true)] 
        [string]$Path,

        [Parameter(Mandatory=$false)]
        [string]$DestinationPath
    )

    $ErrorActionPreference = 'Stop'

    # Test whether the path is exactly a drive letter
    if($Path -match '^[a-zA-Z]:\\$' -or $Path -match '^[a-zA-Z]:$'){
        throw "Path cannot be at the root of a drive. Aborting."
    }

    # Check if the path is valid
    if(-not(Test-Path -Path $Path -PathType Container)){
        throw "Path must describe an existing directory"
    }
    
    # Create the destination path format
    if(-not $PSBoundParameters.ContainsKey('DestinationPath'))
    {
        $DestinationPath = (Get-Item $Path).FullName   ' Folder Copy'
    }

    # Test that the destination isn't an existing file system item
    if(Test-Path -Path $DestinationPath){
        throw "The destination path already exists."
    }

    # If we've reached this point all validation checks passed, begin copy
    robocopy $Path $DestinationPath /e /xf *.* | Out-Null
}

既然函式可以預見地失敗，我們可以使用錯誤處理來處理函式外部的重試邏輯：

while($true){
  $path = Read-Host "Give a target path!"
  try {
    Copy-DirectoryStructure -Path $path
    break
  }
  catch {
    if($_ -match 'The destination path already exists.'){
      $destPath = Read-Host "Wanna try an alternative destination path (input NO to start over)"
      if($destPath -ceq 'NO'){
        continue
      }
      Copy-DirectoryStructure -Path $path
      break
    }
  }
}

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