Question

I have some data that I read from the registry and wish to modify. Example data looks like this:

<User Blob>
    <Item>
        <Key>SomeKey</Key>
        <Value>false</Value>
    </Item>
    <Item>
        <Key>AnotherKey</Key>
        <Value></Value>
    </Item>
</User Blob>
<Primary Server Blob>
    <Item>
        <Key>Just a key</Key>
        <Value></Value>
    </Item>
    <Item>
        <Key>And another key</Key>
        <Value>true</Value>
    </Item>
</Primary Server Blob>

I want to be able to change a certain key’s value. For example:

User Blob.SomeKey = $true

I tried to cast the data to XML or to a HashTable but this gives errors.

Answer 1

Generally, if you have XML data which you wish to modify (not just read), and the data is of a small-enough size (to avoid loading massive objects into memory), you would want to use a Document of some kind. Due to its ability to make use of XPath, I would recommend XmlDocument. (XPath makes this sort of problem simple.)

As you rightly point out though, you will need a single XML root. That’s easy to solve though – just wrap whatever data you have in another root node.

So here’s some code which should do the trick.

$data = @"
<UserBlob>
    <Item>
        <Key>SomeKey</Key>
        <Value>false</Value>
    </Item>
    <Item>
        <Key>AnotherKey</Key>
        <Value></Value>
    </Item>
</UserBlob>
<PrimaryServerBlob>
    <Item>
        <Key>Just a key</Key>
        <Value></Value>
    </Item>
    <Item>
        <Key>And another key</Key>
        <Value>true</Value>
    </Item>
</PrimaryServerBlob>
"@

$wrappedData = "<root>$data</root>"
$doc = new-object Xml.XmlDocument
$doc.LoadXml($wrappedData)
$nodeToChange = $doc.SelectSingleNode("/root/UserBlob/Item[Key='SomeKey']")
if($nodeToChange){
    $nodeToChange.Value = "NEW VALUE"
}
$doc.Save("[PATH_TO_OUTPUT_FILE]")

I’ve omitted error handling and correct disposal of objects for brevity. I’ll leave that up to you. 🙂

For more info about XmlDocument, see the documentation.

UPDATE

To remove the additional root document again, just use this to get it as a string.

$newWrappedData = $doc.Root.InnerXml

Then save the string using a StreamWriter or File.CreateText or something.