PowerShell, XML and XPath

Some of the time, PowerShell makes picking apart an XML file nice and easy by providing properties on the XML object matching nodes; but inevitably you get to a point where there are more than one node of a given type as the child of the one you are at. So then it's time to break out the XPath.

Take a sample XML file (this one being a StyleCop settings file, being to hand, and complicated enough to be interesting):

	<StyleCopSettings Version="4.3">
	<Analyzers>
	<Analyzer AnalyzerId="Microsoft.StyleCop.CSharp.DocumentationRules">
	<Rules>
	<Rule Name="FileMustHaveHeader">
	<RuleSettings>
	<BooleanProperty Name="Enabled">False</BooleanProperty>
	</RuleSettings>
	</Rule>
	<Rule Name="FileHeaderMustShowCopyright">
	<RuleSettings>
	<BooleanProperty Name="Enabled">False</BooleanProperty>
	</RuleSettings>
	</Rule>
	</Rules>
	<AnalyzerSettings />
	</Analyzer>
	</Analyzers>
	</StyleCopSettings>

view raw gistfile1.xml hosted with ❤ by GitHub

And we want to extract the "FileHeaderMustShowCopyright" enabled property. So we can do something like this:

	>[xml] $x = Get-Content "Settings.StyleCop"
	>$x.stylecopsettings.Analyzers.Analyzer.Rules.SelectSingleNode("Rule[@Name='FileHeaderMustShowCopyright']").RuleSettings.SelectSingleNode("BooleanProperty[@Name='Enabled']")
	Name #text
	---- -----
	Enabled False
	>

view raw gistfile1.ps1 hosted with ❤ by GitHub

using PowerShell to navigate where there is no ambiguity, and XPath at each for in the road; or

$x.SelectSingleNode("//Rule[@Name='FileHeaderMustShowCopyright']").RuleSettings.SelectSingleNode("BooleanProperty[@Name='Enabled']")

view raw gistfile1.ps1 hosted with ❤ by GitHub

or

	$x.SelectSingleNode("//Rule[@Name='FileHeaderMustShowCopyright']").SelectSingleNode("//BooleanProperty[@Name='Enabled']")

view raw gistfile1.ps1 hosted with ❤ by GitHub

or simply

$x.SelectSingleNode("//Rule[@Name='FileHeaderMustShowCopyright']//BooleanProperty[@Name='Enabled']")

view raw gistfile1.ps1 hosted with ❤ by GitHub

depending how many of the steps above where we want to end up are of interest.