PowerShell报错排查：输入错误修正后触发&表达式无效对象问题

报错信息 #

管道元素中'&'后的表达式生成了无效对象。它必须生成命令名称、脚本块或CommandInfo对象。

触发场景 #

仅在以下特定场景触发：提示用户输入“y或n”时，用户先输入非y/n的错误响应，被重新提示后输入正确的'y'或'n'；若用户首次输入正确响应，脚本运行完全正常。

相关代码片段 #

function SelectUserGui {
    param(
        $search
    )
    #Returns a gui window to select user
    $selection = Get-ADUser -Filter "surname -like '$search'" -Properties * |
        Select-Object name, samaccountname, DistinguishedName, Enabled, EmployeeID, LockedOut |
        Out-GridView -PassThru -Title 'Choose a user'

    if (-not $selection) {
        Write-Host 'User Not Found / Selection Canceled!!!' -ForegroundColor Red
        Pause
    }
    return $selection
}

function tryAgain {
    param(
        $tryString,
        $funcName
    )

    $x = Read-Host $tryString
    if ($x -eq 'y') {
        & $funcName
    }
    elseif ($x -eq 'n') {
        Clear-Host
        main
    }
    else {
        Write-Host 'Incorrect entry' -ForegroundColor Red
        tryAgain $tryString
        & $funcName
    }
}

function disableUser {
    param (
        $aduser
    )
    $ticketNum = Read-Host "`nEnter the ServiceNow Ticket Number"
    $proceed = Read-Host "`nProceed with disabling for Leave Of Absence? (y or n)"
    if ($proceed -eq 'y') {
        Write-Host 'proceeding ...'
        Write-Host "`n PLEASE ADD FOLLOWING CLOSE NOTES to  TICKET $ticketNum :" -ForegroundColor cyan
        Write-Host "`n Disabled AD account per HR/Workday for LOA `n" -ForegroundColor cyan
        #$target = $ResultsArray[1][$selection]
        $aduser = Get-ADUser -Identity $selection.samaccountname -Properties *
        $prepend = "DISABLED per HR for LOA ($ticketNum) - "
        $desc = $aduser.description
        $loaDesc = $prepend + $desc
        Set-ADUser -Identity $selection.samaccountname -description $loaDesc
        Disable-ADAccount -Identity $selection.samaccountname
        Pause
        #tryAgain
    }
    else {
        Write-Host 'no changes will be made'
        Pause
        #tryAgain
    }
}

function DisableFunc {
    Write-Host "`n  ***** DISABLE USER UTILITY *****  " -ForegroundColor DarkBlue -BackgroundColor white
    $search = promptForUser
    $selection = SelectUserGui $search

    if ($selection.enabled -eq $True) {
        Write-Host "`nYou selected user " -NoNewline
        Write-Host $selection.Name -NoNewline -ForegroundColor Green
        Write-Host ' with user ID a of ' -NoNewline
        Write-Host $selection.samAccountName -NoNewline -ForegroundColor Green
        disableUser $selection
    }
    elseif ($selection.enabled -eq $False) {
        Write-Host "`nUser " -NoNewline
        Write-Host $selection.Name, '(' -NoNewline -ForegroundColor Yellow
        Write-Host $selection.samAccountName -NoNewline -ForegroundColor Yellow
        Write-Host ')' -NoNewline -ForegroundColor Yellow
        Write-Host ' is already ' -NoNewline
        Write-Host 'DISABLED' -NoNewline -ForegroundColor Yellow -BackgroundColor Red
    }

    $tryString = "`nDisable Another User? (y or n)"
    $funcName = 'DisableFunc'
    tryAgain $tryString $funcName
} 

问题根源 #

报错核心在tryAgain函数的递归逻辑：

1. 当用户输入错误时，递归调用tryAgain $tryString，未传入第二个参数$funcName，导致递归过程中$funcName变量值为$null。
2. 递归调用完成后，又执行& $funcName，此时$funcName是$null，不符合&操作符要求的命令名称、脚本块或CommandInfo对象类型，因此触发报错。
3. 额外问题：递归已经处理了用户的正确输入（执行对应逻辑），后续的& $funcName会导致重复执行目标函数。

解决方案 #

修改tryAgain函数，确保递归时传入所有参数，并且移除递归后的多余执行逻辑：

function tryAgain {
    param(
        $tryString,
        $funcName
    )

    $x = Read-Host $tryString
    if ($x -eq 'y') {
        & $funcName
    }
    elseif ($x -eq 'n') {
        Clear-Host
        main
    }
    else {
        Write-Host 'Incorrect entry' -ForegroundColor Red
        # 递归时传入完整参数，且无需后续再执行& $funcName
        tryAgain $tryString $funcName
    }
}

补充优化建议 #

• 可以为Read-Host的输入做大小写兼容，比如$x = (Read-Host $tryString).ToLower()，避免用户输入大写Y/N导致判断失效。
• disableUser函数中直接使用了全局变量$selection，建议改为使用参数$aduser（即$aduser.samaccountname），避免依赖全局变量引发潜在问题。

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