读取包含命名空间PowerShell的XML文件

When you use the Select-Xml cmdlet with the -XPath parameter, you also need to specify the namespace. See this article for more information:

http://huddledmasses.org/xpath-and-namespaces-in-powershell/

Here is a complete, working example

$XmlDocument = [xml]@'
<?xml version="1.0" encoding="utf-8"?>
<ServiceDefinition name="test" xmlns="http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition" schemaVersion="2012-10.1.8">
  <WebRole name="test" vmsize="Small">
    <Sites>
      <Site name="Web">
        <Bindings>
          <Binding name="Endpoint1" endpointName="HttpsEndpoint" />
          <Binding name="Endpoint2" endpointName="HttpEndpoint" />
        </Bindings>
      </Site>
    </Sites>
    <Endpoints>
      <InputEndpoint name="HttpsEndpoint" protocol="https" port="443" certificate="Certificate1" />
      <InputEndpoint name="HttpEndpoint" protocol="http" port="80" />
    </Endpoints>
    <Imports>
      <Import moduleName="Diagnostics" />
      <Import moduleName="RemoteAccess" />
      <Import moduleName="RemoteForwarder" />
    </Imports>
    <Certificates>
      <Certificate name="Certificate1" storeLocation="LocalMachine" storeName="My" />
    </Certificates>
    <ConfigurationSettings>
      <Setting name="LogLevel" />
    </ConfigurationSettings>
  </WebRole>
</ServiceDefinition>
'@;

$XmlNamespace = @{ azure = 'http://schemas.microsoft.com/ServiceHosting/2008/10/ServiceDefinition'; };

Select-Xml -Xml $XmlDocument -XPath '/azure:ServiceDefinition/azure:WebRole/@vmsize' -Namespace $XmlNamespace;