PowerShell脚本更新XML节点值二次执行失效问题求助

我编写了如下PowerShell脚本，用于更新C:\tmp\unzipped\文件夹中多个XML文件的UnitholderId节点值：首次执行脚本时，UnitholderId节点值成功更新为987654，但第二次执行时脚本不再生效，单独处理单个文件也存在相同问题。我是PowerShell脚本新手，不确定遗漏了什么，恳请协助排查。

原PowerShell脚本 #

Get-ChildItem C:\tmp\unzipped\ *.xml | ForEach-Object { 
    $xml = [xml](Get-Content $_)

    $node = $xml.SelectNodes("//RecipientInfoList//UnitholderList")
    $node1 = $xml.SelectNodes("//RecipientInfoList//UnitholderList//List")

    foreach ($nodes in $node) {
        $NodeExists = $nodes.UnitholderId
        if (($nodes.UnitholderId = Null) || $NodeExists) {
            $nodes.UnitholderId = '987654'
        }
    }
    foreach ($nodess in $node1) {
        $NodeExists = $nodes.UnitholderId
        if (($nodes.UnitholderId = Null) || $NodeExists) {
            $nodess.UnitholderId = '987654'
        }
    }
    $xml.Save($_)
}

原XML文件内容 #

<DocumentDelivery>
  <Document>
    <Recipient>
      <RecipientType>INVESTOR COPY</RecipientType>
      <RecipientId>Test123456</RecipientId>
      <RecipientName>TestNameABC</RecipientName>
      <RecipientAddress1>TestAddress 1</RecipientAddress1>
      <RecipientAddress2>TestAddress 2</RecipientAddress2>
      <RecipientAddress3>TestAddress 3</RecipientAddress3>
      <RecipientAddress4>
      </RecipientAddress4>
      <RecipientZipcode>Lb-6012</RecipientZipcode>
      <RecipientCountryCode>GBR</RecipientCountryCode>
      <RecipientCountry>UNITED KINGDOM</RecipientCountry>
      <RecipientFaxNumber>123456</RecipientFaxNumber>
      <RecipientEmail>test@abc.com</RecipientEmail>
      <RecipientContactPerson>
      </RecipientContactPerson>
    </Recipient>
    <RecipientInfoList>
      <UnitholderList>
        <UnitholderId>123456</UnitholderId>
        <List>
        <UnitholderId>123456</UnitholderId>
        </List>
      </UnitholderList>
    </RecipientInfoList>
  </Document>
</DocumentDelivery>

首次执行后的XML文件内容 #

<DocumentDelivery>
  <Document>
    <Recipient>
      <RecipientType>INVESTOR COPY</RecipientType>
      <RecipientId>Test123456</RecipientId>
      <RecipientName>TestNameABC</RecipientName>
      <RecipientAddress1>TestAddress 1</RecipientAddress1>
      <RecipientAddress2>TestAddress 2</RecipientAddress2>
      <RecipientAddress3>TestAddress 3</RecipientAddress3>
      <RecipientAddress4>
      </RecipientAddress4>
      <RecipientZipcode>Lb-6012</RecipientZipcode>
      <RecipientCountryCode>GBR</RecipientCountryCode>
      <RecipientCountry>UNITED KINGDOM</RecipientCountry>
      <RecipientFaxNumber>123456</RecipientFaxNumber>
      <RecipientEmail>test@abc.com</RecipientEmail>
      <RecipientContactPerson>
      </RecipientContactPerson>
    </Recipient>
    <RecipientInfoList>
      <UnitholderList>
        <UnitholderId>987654</UnitholderId>
        <List>
        <UnitholderId>987654</UnitholderId>
        </List>
      </UnitholderList>
    </RecipientInfoList>
  </Document>
</DocumentDelivery>

问题排查与修复 #

问题根源 #

1. 赋值与比较混淆：脚本中用了$nodes.UnitholderId = Null，这是赋值操作而非判断是否为Null的比较操作（正确写法是-eq $null），导致逻辑完全错误。
2. 变量引用错误：第二个foreach循环里错误引用了外层循环的$nodes变量，应该使用当前循环的$nodess。
3. 冗余判断逻辑：试图判断节点是否存在或为空，但实际上可以直接选中所有UnitholderId节点统一赋值，无需复杂判断。

修复后的脚本 #

Get-ChildItem C:\tmp\unzipped\ *.xml | ForEach-Object { 
    $xml = [xml](Get-Content $_)
    # 直接选中所有UnitholderId节点
    $allUnitholderIds = $xml.SelectNodes("//UnitholderId")
    foreach ($idNode in $allUnitholderIds) {
        $idNode.InnerText = '987654'
    }
    $xml.Save($_)
}

说明 #

• 用XPath表达式//UnitholderId可直接选中XML中所有UnitholderId节点，不受层级限制。
• 直接设置节点的InnerText为目标值，无论原节点值是什么，重复执行都会生效。
• 脚本逻辑更简洁，彻底避免了原脚本的变量引用错误和逻辑混乱。

内容的提问来源于stack exchange，提问作者user21418581