Welcome to Windows PowerShell, the new object-based command-line interface shell and scripting language built on top of... more

Welcome to Windows PowerShell, the new object-based command-line interface shell and scripting language built on top of .NET. PowerShell provides improved control and automation of IT administration tasks for the Windows platform. It is designed to make IT professionals and developers more productive.

Several books that introduce end-user IT professionals to Windows PowerShell are already available, but PowerShell development from the perspective of cmdlet, provider, and host developers has gone largely unmentioned. This book attempts to fill that gap by introducing the reader to the concepts, components, and development techniques behind building software packages that leverage Windows PowerShell. This book is written for developers who want to extend the functionality of Windows PowerShell and extend their applications using PowerShell.

Traditionally, when developers write a command-line utility, they have to write code for parsing the parameters, binding the argument values to parameters during runtime. In addition, they have to write code for formatting the output generated by the command. Windows PowerShell makes that easy by providing a runtime engine with its own parser. It also provides functionality that enables developers to add custom formatting when their objects are displayed. By performing the common tasks associated with writing command-line utilities, Windows PowerShell enables developers to focus on the business logic of their application, rather than spend development time solving universal problems.

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As you saw in Chapter 1, Windows PowerShell provides an extensible architecture that allows new functionality to be added... more

As you saw in Chapter 1, Windows PowerShell provides an extensible architecture that allows new functionality to be added to the shell. This new functionality can be in the form of cmdlets, providers, type extensions, format metadata, and so on. A Windows PowerShell snap-in is a .NET assembly that contains cmdlets, providers, and so on. Windows PowerShell comes with a set of basic snap-ins that offer all the basic cmdlets and providers built into the shell. You write a snap-in when you want your cmdlets or providers to be part of the default Windows PowerShell. When a snap-in is loaded in Windows PowerShell, all cmdlets and providers in the snap-in are made available to the user. This model allows administrators to customize the shell by adding or removing snap-ins to achieve precise sets of providers and cmdlets.

This chapter first introduces the two types of PowerShell snap-ins and describes when to use each one. It then shows you step by step, how to author, register, and use both types of snap-ins. To make it more meaningful, the code examples also show the minimum coding needed for authoring cmdlets.

Note that all code examples in this chapter and the rest of the book are written in C#.

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All languages use a type system to define values and expressions into types. PowerShell is built on top of the .NET Framework... more

All languages use a type system to define values and expressions into types. PowerShell is built on top of the .NET Framework and it uses the .NET Framework as its type system. However, the .NET Framework is designed for use with compiled programming languages and is targeted toward developers; it is neither designed for the scripting environment nor suitable for use by scripters. To solve this problem, Windows PowerShell extends the .NET Framework to form an Extended Type System (ETS). The ETS forms the core of the Windows PowerShell language’s type system. Specifically, the ETS provides PSObject, which is the object created whenever new objects or variables are created in Windows PowerShell. PSObject provides the necessary access to the Windows PowerShell type system.

For scripters, PSObject provides a uniform interface to the different types of objects that can be created in .NET, COM, WMI, ADSI, and so on. For developers, it provides a mechanism to manipulate the objects and structured data using same syntax as CLR class. In addition to the aforementioned functionality, the ETS provides the capability to extend original objects so that they can better serve in the scripting environment. It provides the foundation of a malleable type system, enabling the script developer to define types dynamically and so that the rest of the PowerShell system knows how to work with that object.

This chapter describes the different components of the Windows PowerShell type system. First we start with PSObject, the core of the system. Then we will look at other features, including type extensions, type adapters, type conversion, and how a scripter or a developer can use these different features to dynamically manage an object. Finally, we end the chapter by looking at different built-in type adapters.

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Developing cmdlets is one of the most common and powerful ways to extend PowerShell functionality.... more

Developing cmdlets is one of the most common and powerful ways to extend PowerShell functionality. This chapter explains different aspects of authoring PowerShell cmdlets.

In a traditional shell such as a Unix shell or DOS’s cmd.exe, each command is a standalone executable. Developing traditional command executables involves the following tasks:

• Parsing command lines, which normally includes command name, command parameter, and command arguments

• Processing command input, which normally is in text format

• Performing command logic, which can involve transforming command input into a different format for easier processing

• Generating command output, which typically is text writing to a console or outputting to a file

• Reporting errors in case command invocation is not successful

Unlike traditional commands, PowerShell cmdlets are .NET classes hosted in a PowerShell runtime environment. As a result, chores such as command-line parsing, input and output processing, and error reporting can be greatly simplified. This chapter illustrates how.

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Provider is a common term used in computer science to describe a service or interface for accessing some form of data.... more

Provider is a common term used in computer science to describe a service or interface for accessing some form of data. ADO.NET, for example, is a data provider model for accessing databases. It presents a consistent interface for accessing the rows and tables in the database. By implementing a data provider for a particular database or backend data store, applications can access the data in the same way, regardless of how the data is stored in the backend. This enables the business logic of an application to decouple itself from the details of which database it’s accessing—at least, that’s the theory.

In the case of PowerShell, providers present consistent interfaces via the provider cmdlets to custom data stores. There are several types of providers in PowerShell and developers must choose which one to use for controlling access to their data store.

Each provider interface or base class is an abstraction of the relationships of the data and the operations performed on that data. Different types of data storage present their own unique complexities and thus have different patterns of usage. This has led to several different interfaces and classes that you can derive from when implementing your provider. How you want your data to be accessed will dictate what interfaces you implement.

Like cmdlets, providers are compiled into a .NET assembly and included in your PowerShell session via snap-ins. Unlike cmdlets, however, once the add-pssnapin command is executed, any providers in that snap-in are initialized and added. See Chapter 2 for information about how to create a snap-in containing your provider.

This chapter explains how to write a provider and describes the multiple design decisions that affect which interfaces or features to implement. For overall information regarding how providers work, execute the command get-help about_provider.

This chapter is comprised of several sections that take a layer-based approach to explaining how to develop a provider. The example providers are covered in the order of least complex to most complex. Each of the different provider types is demonstrated with a sample XML provider that ultimately enables you to navigate, copy, or remove nodes from an XML document you map as a PSDrive. We also use a stripped down filesystem provider to illustrate the property and content provider interfaces.

Note that the CD for this book contains several sample providers. Some of the methods from them are discussed throughout this chapter.

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Assuming you’ve tried out Windows PowerShell prior to reading this, you’re familiar with PowerShell’s... more

Assuming you’ve tried out Windows PowerShell prior to reading this, you’re familiar with PowerShell’s console host, which is the user interface that shows you the prompt, accepts your commands, and displays their results. In most command shells, no distinction is visible between the front-end application and the back-end execution engine—to the user, it’s all one monolithic executable.

From a command-line user’s perspective, the same might seem true of Windows PowerShell. To the .NET developer, however, the PowerShell execution engine exposes a public API that enables it be called independently of the console host, providing a powerful means of integrating PowerShell functionality into .NET applications.

In this chapter, you’ll learn how the PowerShell engine’s public API can be used for integrating PowerShell into managed code applications. Along the way, you’ll be introduced to several classes and concepts that make this possible.

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As you saw in Chapter 6, the Windows PowerShell hosting engine provides access to output, error, and input streams of... more

As you saw in Chapter 6, the Windows PowerShell hosting engine provides access to output, error, and input streams of a pipeline. The Windows PowerShell engine also provides a way for cmdlet and script writers to generate other forms of data such as verbose, debug, warning, progress, and prompts. In this chapter, you will learn how a hosting application can register with the Windows PowerShell engine and get access to these and other forms of data.

An application can host Windows PowerShell using the Pipeline, Runspace, and RunspaceInvoke API, as shown in Chapter 6. However, to get the other aforementioned data, the hosting application has to provide an implementation of System.Management.Automation.Host.PSHost. In fact, powershell.exe, the Windows PowerShell startup application implements one such host, Microsoft.PowerShell.ConsoleHost.

This chapter begins by explaining how the Windows PowerShell engine interacts with a host, and then describes different built-in cmdlets that interact with a host. It also explores different classes such as PSHost, PSHostUserInterface, and PSHostRawUserInterface that make up a host.

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Formatting & Output is a single component of PowerShell that determines how objects are displayed to the console.... more

Formatting & Output is a single component of PowerShell that determines how objects are displayed to the console. PowerShell enables users to provide custom formatting for types they create or types that already exist in .NET or PowerShell. This custom formatting is controlled via several configuration files, with the file naming convention of *.format.ps1xml. These configuration files are used by the format cmdlets (format-table, format-list, format-custom, format-wide) to display text to the screen for the default console host (powershell.exe). The best way to ensure that objects are displayed in a consistent manner is to add your own “views” by creating your own format configuration file and adding them to the current session. Adding your configuration file to the current session is done by using the update-formatdata cmdlet or by including your file(s) with a snap-in.

This chapter provides an introduction to creating your own views for the different view types. Included are several examples of format configuration, which can be used as a baseline for your own custom formatting.

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Windows PowerShell uses a verb-noun pair format to name cmdlets. When you are naming your cmdlets,... more

Windows PowerShell uses a verb-noun pair format to name cmdlets. When you are naming your cmdlets, you should specify the verb part of the name using one of the predefined verb names provided in the following tables. By using one of these predefined verbs, you ensure consistency between the cmdlets you create and those provided by Windows PowerShell and others.

The following lists of verbs are officially recommended by Microsoft. For the latest information, please refer to documents in the PowerShell SDK.

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Parameter names should be consistent across different cmdlets. Windows PowerShell defines and recommends the parameter... more

Parameter names should be consistent across different cmdlets. Windows PowerShell defines and recommends the parameter names provided in this appendix. Cmdlet developers should choose from this list when possible. The tables presented here list recommended parameters from the following categories:

• Ubiquitous parameters

• Activity parameters

• Date/Time parameters

• Format parameters

• Property parameters

• Quantity parameters

• Resource parameters

• Security parameters

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A key mechanism that enables the off-the-shelf parameter binding available to cmdlet developers is PowerShell’s... more

A key mechanism that enables the off-the-shelf parameter binding available to cmdlet developers is PowerShell’s cmdlet metadata. Cmdlet metadata is a set of .NET custom attribute types that are applied to cmdlet classes and their members, and which provide the PowerShell execution engine with information necessary to run the cmdlets. Along with derivation from the cmdlet base classes, cmdlet metadata is what makes a .NET class a cmdlet.

The metadata attributes can be grouped into three general sets: the CmdletAttribute class, which is applied to the cmdlet class itself; the Parameter and Alias attributes, which are used to indicate that public properties and fields are cmdlet parameters; and the validation and transformation attributes, which enable a cmdlet developer to set restrictions on incoming data. One of the validation attributes, ValidateArgumentsAttribute, is not applied to parameters directly, but can be inherited and extended for custom validation and transformation.

Besides being directly applied to cmdlet parameters in code, the parameter metadata attributes can also be created at runtime and applied to dynamically created pseudo-parameters of cmdlets, and to the Attributes collection of PowerShell session-state variables.

This appendix serves as a reference describing the cmdlet metadata attribute classes, and provides examples of their use.

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This appendix lists cmdlet provider base classes and interfaces that you may derive from to implement a PowerShell provider.... more

This appendix lists cmdlet provider base classes and interfaces that you may derive from to implement a PowerShell provider. A brief description is provided along with each method and property.

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This appendix lists the cmdlets shipped with Windows PowerShell that directly interact with different provider interfaces.... more

This appendix lists the cmdlets shipped with Windows PowerShell that directly interact with different provider interfaces. All these cmdlets are common cmdlets that work with any provider. The provider must, however, implement certain interfaces or derive from certain classes to take advantage of these cmdlets. The following sections describe these common cmdlets and what a provider implementation must do to take advantage of them.

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