Now that I've got some reasonably terse syntax working for Tridion scripting, it's time to start building out some tooling to make the whole thing useful. It's quite often useful to be able to enumerate everything in your Tridion system, so walking the tree is a basic operation. You don't want to write the tree walk every time you have a different operation to perform, so it's handy to abstract the mechanics of the recursion out into a function. Somewhere in the nether regions of this blog, you'll find a JavaScript implementation of such a function. The basic technique I used in JavaScript was to have my tree-walking function accept a "process" function as an argument. For each item in your system, this is invoked, and is able to perform whatever processing is necessary on your item. (In the JavaScript version, I actually had two functions: process and filter. The filter function was responsible for deciding whether the item was interesting to process. In practice, this is probably too much abstraction. You can just as easily code an if-block in your process function, so on this occasion I'm restricting myself to just the one.)

To anyone who has written any JavaScript, it's pretty much impossible to miss the fact that functions are first-class objects. It may not be immediately apparent that this is true in Powershell, but it is. A Script Block in Powershell, is simply an anonymous function, and you can pass them around in variables or as parameters to other functions. (These days, the concept isn't even weird to C# hackers, what with lambda expressions and all.)

So - here goes: if you start with the function "recurseTridionItems" shown below....

import-module Reflection
import-namespace Tridion.ContentManager.CoreService.Client

function recurseTridionItems{
	Param(
	[parameter(Mandatory=$true)]
	[ValidateNotNullOrEmpty()]
	[SessionAwareCoreServiceClient]$core, 
	[IdentifiableObjectData]$parent, 
	[ScriptBlock]$scriptblock,
	[int]$level = 0
	)
	$ro = new-object ReadOptions
	if ($parent -eq $null){
		[PublicationData[]]$items = @($core.GetSystemWideList((new-object PublicationsFilterData)))
		foreach ($item in $items) {
			$fullItem = $core.Read($item.Id, $ro)
			&$Scriptblock $fullItem $level
			recurseTridionItems $core $fullItem $scriptblock ($level + 1)
		}
	}
	else {
		if ($parent -is [OrganizationalItemData]){
			$items = $core.GetList($parent.Id, (new-object OrganizationalItemItemsFilterData))
		} else {
			$items = $core.GetList($parent.Id, (new-object RepositoryItemsFilterData))
		}

		foreach($item in $items) {
			$fullItem = $core.Read($item.Id, $ro)
			&$Scriptblock $fullItem $level
			if ($fullItem -is [PublicationData]) {
				recurseTridionItems $core $fullItem $scriptblock ($level + 1)
			} elseif ($item -is [OrganizationalItemData]) {
				recurseTridionItems $core $fullItem $scriptblock ($level + 1)
			}
		}
	}
}

... this will take care of all the tree walking. For an example to show how you might use this, I've written a script block that outputs the Title of the item, indented based on the recursion level.

EDIT: my first version of this function didn't re-read the items that come from GetList. It worked fine for the trivial case of listing the titles but as soon as I tried anything more interesting, I discovered that GetList returns objects that are only partially loaded. This is apparently by design, as the documentation mentions it.

recurseTridionItems $core $null {param($item,$level)"`t" * $level + $item.Title}

On my system, this produces output like this:

_Empty Master
        Building Blocks
                Default Templates
                        Outbound E-mail
                                Generate Plain Text E-mail
                                Outbound E-mail Post-processing
                                Outbound E-mail Pre-processing
                                Generate Plain Text E-mail
                                Outbound E-mail Post-processing
                                Outbound E-mail Pre-processing
                                Set Output Item By Email Mode
                                Tridion.OutboundEmail.Templating.Templates
                        SDL External Content Library
                                Adjust SiteEdit 2009 markup for External Content Library i
                                Adjust SiteEdit 2012 markup for External Content Library i
                                Resolve External Content Library items
                                Search External Content Library items
                                Tridion.ExternalContentLibrary.Templating
                        Component Query
                        Convert Html to Xml
                        Convert Xml to Html
                        Default Finish Actions
                        Dreamweaver Region Selection
                        Enable inline editing for content
                        Enable inline editing for Page
                        Extract Binaries from Html
                        Image Resizer
                        Link Resolver
                        Publish Binaries in Package
                        Default Component Template
                        Default Component Template for UGC
                        Default Page Template
                        Default Page Template for UGC
                        Activate Tracking
                        Cleanup Template
                        Component Query
                        Convert Html to Xml
                        Convert Xml to Html
                        Default Dreamweaver Component Design
                        Default Dreamweaver Page Design
                        Default Finish Actions
                        Default UGC Dreamweaver Template design
                        Enable inline editing for content
                        Enable inline editing for Page
                        Enable User Generated Content Processing
                        Extract Binaries from Html
                        Extract Components from Page
                        Image Resizer
                        Link Resolver
                        Publish Binaries in Package
                        Sample XSLT Component Design
                        Target Group Personalization
                        Tridion.SiteEdit.Templating
                        Tridion.Ugc.Templating.DefaultTemplates
                Default Multimedia Schema
        root
01 Definitions
        Building Blocks
                Default Templates
                        Outbound E-mail
                                Generate Plain Text E-mail

I think I'll truncate it there: you get the picture. Obviously, this is a trivial use-case that probably isn't terribly useful on an industrial scale installation. Fortunately, your script-block doesn't have to be a one-liner, and you can easily expand on this technique to meet your own needs. I should think I'll find quite a few uses for it myself. Just one word of caution: this was just a quick hack, and I haven't tested it exhaustively.