如何让RoboCopy脚本中-WhatIf的输出格式整洁规范？

问题场景 #

我尝试在RoboCopy的PowerShell脚本中实现-WhatIf标志（请将user替换为你的用户配置文件）：

[CmdletBinding(SupportsShouldProcess)]
param (
    $Purge = $false
)

$RCCommand = "Robocopy C:\Users\user\Desktop\Source C:\Users\user\Desktop\Target"
$WhatIfMessage = Invoke-Expression "$RCCommand /L"

if ($PSCmdlet.ShouldProcess($WhatIfMessage, $WhatIfMessage, 'Are you sure?')) {
    Invoke-Expression $RCCommand
}

使用该脚本时，-WhatIf的输出格式混乱，所有内容挤成一团：

> .\Desktop\Invoke-RoboCopy.ps1 -WhatIf
What if:  -------------------------------------------------------------------------------    ROBOCOPY     ::     Robust File Copy for Windows                               -------------------------------------------------------------------------------    Started : Monday, June 2, 2025 19:47:55    Source : C:\Users\user\Desktop\Source\      Dest : C:\Users\user\Desktop\Target\      Files : *.*                Options : *.* /L /DCOPY:DA /COPY:DAT /R:1000000 /W:30   ------------------------------------------------------------------------------                      1    C:\Users\user\Desktop\Source\    *EXTRA Dir        -1     C:\Users\user\Desktop\Target\NotSource\   *EXTRA Dir        -1    C:\Users\user\Desktop\Target\Source1\  ------------------------------------------------------------------------------                 Total    Copied   Skipped  Mismatch    FAILED    Extras     Dirs :         1         0         1         0         0         2    Files :         1         0         1         0         0         0    Bytes :         0         0         0         0         0         0    Times :   0:00:00   0:00:00                       0:00:00   0:00:00    Ended : Monday, June 2, 2025 19:47:55

但直接输出$WhatIfMessage时，格式却很整洁：

[CmdletBinding(SupportsShouldProcess)]
param (
    $Purge = $false
)

$RCCommand = "Robocopy C:\Users\user\Desktop\Source C:\Users\user\Desktop\Target"
$WhatIfMessage = Invoke-Expression "$RCCommand /L"
$WhatIfMessage

输出结果：

> .\Desktop\Invoke-RoboCopy.ps1

-------------------------------------------------------------------------------
   ROBOCOPY     ::     Robust File Copy for Windows
-------------------------------------------------------------------------------

  Started : Monday, June 2, 2025 19:48:19
   Source : C:\Users\user\Desktop\Source\
     Dest : C:\Users\user\Desktop\Target\

    Files : *.*

  Options : *.* /L /DCOPY:DA /COPY:DAT /R:1000000 /W:30

------------------------------------------------------------------------------

                           1    C:\Users\user\Desktop\Source\
        *EXTRA Dir        -1    C:\Users\user\Desktop\Target\NotSource\
        *EXTRA Dir        -1    C:\Users\user\Desktop\Target\Source1\

------------------------------------------------------------------------------

               Total    Copied   Skipped  Mismatch    FAILED    Extras
    Dirs :         1         0         1         0         0         2
   Files :         1         0         1         0         0         0
   Bytes :         0         0         0         0         0         0
   Times :   0:00:00   0:00:00                       0:00:00   0:00:00
   Ended : Monday, June 2, 2025 19:48:19

问题原因 #

ShouldProcess方法会将传入的消息视为单行文本，自动把其中的换行符替换成空格，导致RoboCopy原本带格式的多行输出被挤压成一团，破坏了原有排版。

解决方案 #

方法一：手动处理-WhatIf逻辑 #

直接检查$WhatIfPreference变量，当用户指定-WhatIf时，直接输出RoboCopy的模拟运行结果；否则执行实际复制操作。这种方式能完整保留RoboCopy的输出格式：

[CmdletBinding(SupportsShouldProcess)]
param (
    $Purge = $false
)

$RCCommand = "Robocopy C:\Users\user\Desktop\Source C:\Users\user\Desktop\Target"
$RCWhatIfCommand = "$RCCommand /L"

if ($WhatIfPreference) {
    Write-Host "=== WhatIf 模拟运行结果 ==="
    Invoke-Expression $RCWhatIfCommand
} else {
    if ($PSCmdlet.ShouldProcess("执行RoboCopy同步操作", "确认执行源目录到目标目录的同步？", "RoboCopy同步")) {
        Invoke-Expression $RCCommand
    }
}

方法二：自定义ShouldProcess提示+单独输出模拟结果 #

如果仍想保留ShouldProcess的确认提示逻辑，可以将简洁的提示文本传入ShouldProcess，同时在进入WhatIf模式时单独输出RoboCopy的模拟结果：

[CmdletBinding(SupportsShouldProcess)]
param (
    $Purge = $false
)

$RCCommand = "Robocopy C:\Users\user\Desktop\Source C:\Users\user\Desktop\Target"
$RCWhatIfCommand = "$RCCommand /L"

if ($PSCmdlet.ShouldProcess("源目录到目标目录的文件同步", "确认执行同步？", "RoboCopy操作")) {
    if ($WhatIfPreference) {
        Write-Host "`n=== 模拟运行详情 ==="
        Invoke-Expression $RCWhatIfCommand
    } else {
        Invoke-Expression $RCCommand
    }
}

说明 #

两种方法都能让-WhatIf的输出保持RoboCopy原生的整洁格式，方法一更直接，适合只需要模拟输出的场景；方法二则保留了ShouldProcess的交互式确认能力，适合需要用户确认后再执行的场景。

内容的提问来源于stack exchange，提问作者gargoylebident