How do I alter XML with PowerShell/XPath and save the document?

Question

I'm looking to use PowerShell to alter XML. I haven't been able to copy XML using XPath. I can load the XML, but I can't figure out how to list the XML with an XPath and create another XML file with what I retrieve.

$doc = new-object "System.Xml.XmlDocument"
$doc.Load("XmlPath.xml")

Also, how would you add the removed XML to another XML file?

Answer 1

If you're using PowerShell 2.0 you can use the new Select-Xml cmdlet to select xml based on an XPath expression e.g.:

$xml = '<doc><books><book title="foo"/></books></doc>'
$xml | Select-Xml '//book'
Node    Path          Pattern
----    ----          -------
book    InputStream   //book

To remove nodes:

PS> $xml =[xml]'<doc><books><book title="foo"/><book title="bar"/></books></doc>'
PS> $xml | Select-Xml -XPath '//book' | 
        Foreach {$_.Node.ParentNode.RemoveChild($_.Node)}

title
-----
foo
bar

PS> $xml.OuterXml
<doc><books></books></doc>

Then to save to file:

$xml.Save("$pwd\foo.xml")
Get-Content foo.xml
<doc>
  <books>
  </books>
</doc>

Answer 2

Load Linq Xml assemblies:

[System.Reflection.Assembly]::LoadWithPartialName("System.Xml.Linq")
[System.Reflection.Assembly]::LoadWithPartialName("System.Xml.XPath")

Load your xml (Note, you can use ::Load("file") instead of ::Parse(...) to load from file:

$xml = [System.Xml.Linq.XDocument]::Parse("<root> <row>Hey</row> <row>you</row> </root>")

Modify (in this case Remove the first row:

[System.Xml.XPath.Extensions]::XPathSelectElement($xml, "//row").Remove()

Save to file:

$xml.Save("MyXml.xml")

Using System.Xml (instead of System.Xml.Linq):

$doc = new-object "System.Xml.XmlDocument"
$doc.Load("MyXml_int.xml")

$node = $doc.SelectSingleNode("//row");
$node.ParentNode.RemoveChild($node)

$doc.Save("MyXml_out.xml")