Using PowerShell to Read and Write XML

Posted on May 4, 2023 by Kae

This blog provides a simple example of using PowerShell to read and write XML nodes and attribute names.

Using PowerShell to Write XML

In this example, we first create a new [System.Xml.XmlDocument] object to represent our XML document. We then create a root node and append it to the document. We create a child node, add an attribute and inner text, and append it to the root node.

Finally, we save the XML document to a file using the Save method.

# Create new XML document
$xml = New-Object -TypeName System.Xml.XmlDocument

# Create root node
$root = $xml.CreateElement("RootNode")
$xml.AppendChild($root)

# Create child node with attribute and value
$child = $xml.CreateElement("ChildNode")
$child.SetAttribute("AttributeName", "AttributeValue")
$child.InnerText = "Inner text"
$root.AppendChild($child)

# Save XML to file
$xml.Save("C:\alkane\example.xml")

Using PowerShell to Read XML

In this example, we first load an XML file using the Get-Content cmdlet and cast it as an [xml] object using the PowerShell type accelerator. We can then access specific elements and attributes within the XML document using dot notation.

# Load XML file
[xml]$xml = Get-Content -Path C:\alkane\example.xml

# Access XML elements and attributes
$xml.RootNode.ChildNode.AttributeName
$xml.RootNode.ChildNode.InnerText

Using PowerShell to Iterate Through XML Nodes and Attributes

Let’s suppose our XML file has more than one child node like so:

# Create new XML document
$xml = New-Object -TypeName System.Xml.XmlDocument

# Create root node
$root = $xml.CreateElement("RootNode")
$xml.AppendChild($root)

# Create child node with attribute and value
$child = $xml.CreateElement("ChildNode")
$child.SetAttribute("AttributeName", "AttributeValue1")
$child.InnerText = "Inner text 1"
$root.AppendChild($child)

# Create another child node with attribute and value
$child = $xml.CreateElement("ChildNode")
$child.SetAttribute("AttributeName", "AttributeValue2")
$child.InnerText = "Inner text 2"
$root.AppendChild($child)

# Save XML to file
$xml.Save("C:\alkane\example.xml")

We might then want to loop through these child nodes to read each node text and attribute. We can do this like so:

# Load XML file
[xml]$xml = Get-Content -Path C:\alkane\example.xml

# Loop through nodes and attributes
foreach ($node in $xml.RootNode.ChildNodes) {
    Write-Host "Node name: $($node.Name)"
    Write-Host "Node value: $($node.InnerText)"
    
    foreach ($attribute in $node.Attributes) {
        Write-Host "Attribute name: $($attribute.Name)"
        Write-Host "Attribute value: $($attribute.Value)"
    }
}

XML declaration allowed only at the start of the document

Posted on June 3, 2019 by Kae

When I viewed any RSS (XML) page on my WordPress site, the page didn’t render correctly and instead displayed an error stating: XML declaration allowed only at the start of the document.

Upon viewing the page source I could see that the first line in the document was in fact blank line, and the second line contained the usual XML declaration:

<?xml version="1.0" encoding="UTF-8"?>

But what was causing it?

It turned out that the problem was with my custom theme. In Functions.php in my child theme folder, I had whitespace before the starting <?php and after the ending ?>. Once I deleted this whitespace and re-uploaded Functions.php to my web server, the blank first line was gone and all of my RSS pages rendered successfully! Hopefully this will enable you to solve the error message: XML declaration allowed only at the start of the document.

Cascading Dropdown List using VBScript, XPATH and an XML back-end

Posted on August 1, 2013 by Kae

I’ve been working on more toolsets recently, and we needed a way to populate multiple dropdown lists in a HTA file, and make them cascade. Cascading is basically where the results in the second dropdown list are dictated by the selection in the first dropdown list. For example:

Let’s say our first dropdown list contained car manufacturers, and the second dropdown list contained models. If I selected ‘Ford’ from the manufacturers dropdown list, I would want the model dropdown list to show me a list of all cars made by Ford (Fiesta, Mondeo, Escort etc etc) and so on.

Anyway, in our example we’ll use a good ol’ list of football clubs. In dropdown list 1, we want a list of football clubs. And in dropdown list 2, we want to see a list of players. We also want to keep track of the stadium that each clubs plays in. Here’s our sample XML chunk – we’ll call it ‘footballclubs.xml’:

<?xml version="1.0"?>
<PREMIERLEAGUEFOOTBALLCLUBS>
	<FOOTBALLCLUBS>
		<FOOTBALLCLUB>
			<FOOTBALLCLUBNAME>Manchester United FC</FOOTBALLCLUBNAME>
			<FOOTBALLCLUBSTADIUM>Old Trafford</FOOTBALLCLUBSTADIUM>
			<PLAYERS>				
				<PLAYER>
					<PLAYERNAME>Rio Ferdinand</PLAYERNAME>
				</PLAYER>		
				<PLAYER>
					<PLAYERNAME>Nemanja Vidic</PLAYERNAME>
				</PLAYER>				
			</PLAYERS>
		</FOOTBALLCLUB>
		<FOOTBALLCLUB>
			<FOOTBALLCLUBNAME>Chelsea FC</FOOTBALLCLUBNAME>
			<FOOTBALLCLUBSTADIUM>Stamford Bridge</FOOTBALLCLUBSTADIUM>
			<PLAYERS>				
				<PLAYER>
					<PLAYERNAME>Frank Lampard</PLAYERNAME>
				</PLAYER>				
			</PLAYERS>
		</FOOTBALLCLUB>
		<FOOTBALLCLUB>
			<FOOTBALLCLUBNAME>Arsenal FC</FOOTBALLCLUBNAME>
			<FOOTBALLCLUBSTADIUM>Emirates Stadium</FOOTBALLCLUBSTADIUM>
			<PLAYERS>				
				<PLAYER>
					<PLAYERNAME>Keiron Gibbs</PLAYERNAME>
				</PLAYER>		
				<PLAYER>
					<PLAYERNAME>Jack Wilshere</PLAYERNAME>
				</PLAYER>
				<PLAYER>
					<PLAYERNAME>Aaron Ramsey</PLAYERNAME>
				</PLAYER>				
			</PLAYERS>
		</FOOTBALLCLUB>		
	</FOOTBALLCLUBS>
</PREMIERLEAGUEFOOTBALLCLUBS>

You can see that the football clubs are: Manchester Utd, Chelsea and Arsenal. You should also be able to see the players for each club, and the stadium they play in.

Now we’ll write a HTA file, and save it in the same location as ”footballclubs.xml’:

<html>
<head>
<hta:application
 id="oHTA"
 applicationname="XML Cascading Drop Down"
 singleinstance="yes"
 windowstate="normal"
 border="no"
 maximize="no"
 caption="XML Cascading Drop Down"
 icon="alkane.ico"
 showintaskbar="yes"
 sysmenu="yes"> 
<title>XML Cascading Drop Down 1.0.0</title>
</head>

<script language="vbscript">

' *************
'
' Version 1.0.0
'
'**************

Option Explicit

Dim strXMLFile

Sub InitialWindow

	Dim intHorizontal, intVertical, intLeft, intTop, objItem	

	Dim menu_width : menu_width = "450"
	Dim menu_height : menu_height = "420"	

	' This moves the window to the middle of the screen
	Dim objWMIService : Set objWMIService = GetObject("winmgmts:\\.\root\cimv2") 
	Dim colItems : Set colItems = objWMIService.ExecQuery("Select * From Win32_DesktopMonitor WHERE DeviceID='DesktopMonitor1'") 

	For Each objItem in ColItems 
		intHorizontal = objItem.ScreenWidth 
		intVertical = objItem.ScreenHeight 
	Next 

	intLeft = (intHorizontal - menu_width)/2 
	intTop = (intVertical - menu_height)/2 
	window.resizeTo menu_width,menu_height 
	window.moveTo intLeft, intTop

	strXMLFile = FindCurrentDir & "footballclubs.xml"		

	Call PopulateDropdownLists

End Sub

Function FindCurrentDir

	Dim objShell : Set objShell = CreateObject("WScript.Shell")
	FindCurrentDir = Left(document.location.pathname,InStrRev(document.location.pathname,"\"))

End Function

Sub PopulateDropdownLists

	Dim objOption
	Dim strQuery, colItem, objItem

	Const intForReading = 1

	Dim xmlDoc : Set xmlDoc = CreateObject( "Microsoft.XMLDOM" )
	xmlDoc.Async = False

	If xmlDoc.Load(strXMLFile) Then

		'populate club names

		Set objOption = Document.createElement("OPTION")
		objOption.Text = "Select Club"
		objOption.value = "Select Club"
		ClubSelector.add(objOption)

		strQuery = "/PREMIERLEAGUEFOOTBALLCLUBS/FOOTBALLCLUBS/FOOTBALLCLUB/FOOTBALLCLUBNAME"	
		Set colItem = xmlDoc.selectNodes(strQuery)

		For Each objItem in colItem	
			Set objOption = Document.createElement("OPTION")
			objOption.Text = objItem.text
			objOption.value = objItem.text
			ClubSelector.add(objOption)		
		Next

		Set objOption = Document.createElement("OPTION")
		objOption.Text = "Select Player"
		objOption.value = "Select Player"
		PlayerSelector.add(objOption)	

	End If

	Set xmlDoc = Nothing

End Sub

Sub populateClubs()

	Dim footballclubname : footballclubname = ClubSelector.options(ClubSelector.SelectedIndex).value
	Dim objOption

	For Each objOption in PlayerSelector.Options
		objOption.RemoveNode
	Next 	

	Dim xmlDoc : Set xmlDoc = CreateObject("Microsoft.XMLDOM")
	xmlDoc.Async = False

	Set objOption = Document.createElement("OPTION")
	objOption.Text = "Select Player"
	objOption.value = "Select Player"
	PlayerSelector.add(objOption)

	If xmlDoc.Load(strXMLFile) Then

		dim strQuery : strQuery = "/PREMIERLEAGUEFOOTBALLCLUBS/FOOTBALLCLUBS/FOOTBALLCLUB [ FOOTBALLCLUBNAME = '" & footballclubname & "' ] /PLAYERS/PLAYER/PLAYERNAME"
		dim colItem : Set colItem = xmlDoc.selectNodes(strQuery)
		dim objItem

		For Each objItem in colItem
			Set objOption = Document.createElement("OPTION")
			objOption.Text = objItem.text
			objOption.value = objItem.text
			PlayerSelector.add(objOption)	
		Next
	End If

	Set xmlDoc = Nothing		

End Sub

Function getXMLValues(footballclubname,tag)

	Dim xmlDoc : Set xmlDoc = CreateObject( "Microsoft.XMLDOM" )
	xmlDoc.Async = False

	If xmlDoc.Load(strXMLFile) Then
		dim strQuery : strQuery = "/PREMIERLEAGUEFOOTBALLCLUBS/FOOTBALLCLUBS/FOOTBALLCLUB [ FOOTBALLCLUBNAME = '" & footballclubname & "' ] /" & tag & ""
		dim colItem : Set colItem = xmlDoc.selectNodes(strQuery)
		dim objItem

		For Each objItem in colItem
			getXMLValues = objItem.text
		Next
	End If

	Set xmlDoc = Nothing	

End Function

Sub displayStadium

	Dim footballclubname : footballclubname = ClubSelector.options(ClubSelector.SelectedIndex).value	
	Dim stadiumname : stadiumname = getXMLValues(footballclubname,"FOOTBALLCLUBSTADIUM")	
	MsgBox stadiumname

End Sub

</script>

<body scroll="no" onload="InitialWindow" style="text-align:center;font-family:Arial;font-size:12px;">

	<br /><br />
	<select size="1" id="ClubSelector" onChange="populateClubs()"></select><br /><br />
	<select size="1" id="PlayerSelector"></select><br /><br />

	<input type="button" value="Display Stadium" name="printSelection"  onClick="displayStadium()" />

</div>

</body>
</html>