Pillars of PowerShell: Commanding

Introduction

This is the second blog post as a continuance in the series on the Pillars of PowerShell. In the initial blog post we went over the various interfaces that can be used to work with PowerShell. In this blog post we are going to start out by going through a few terms you might find when you start reading up on PowerShell. Otherwise, I will go over three of the cmdlets you will find can be used to discover and get documentation on the cmdlets available to you in PowerShell.

Pillar 2: Commanding

The following are a few terms I will use throughout this series, and ones you might find referenced in any reading material, which I wanted to introduce so we start out on the same page:

Session
When you open PowerShell.exe or PowerShell_ISE.exe it will create a session for you, essentially a blank slate for you to build and create. You can think of this as a query window within the SQL Server Management Studio.
Cmdlets
Pronounced “command-lets”, these are the bread and butter of PowerShell that allow you to do things from getting information or manipulating it. Microsoft has coined the format of Verb-Noun for the cmdlets and it has pretty much stuck. Each version of PowerShell as it is released comes with additional cmdlets, and then product teams like SQL Server and Active Directory are also releasing cmdlets to allow you to interact with them through PowerShell. Each time you open a session with PowerShell there are a set of core cmdlets that are automatically loaded for you.
Module
A module is basically just a set of cmdlets that can be added within your session of PowerShell. When you load a module into your session, the commands are then made available to you. If you close that session and open a new one, you will then have to reload that module to access the commands again.
Objects
PowerShell is based on .NET, this is what is behind the scenes more or less, thus with .NET being an object oriented language PowerShell treats the data that is returned as objects. So, if I use a cmdlet to return the processes running on a machine, each process that it returns is as an object.
The Pipeline
This is named after the symbol used to connect cmdlets together, “|” (vertical bar on your keyboard). You can think of this like a train, each train car represents a set of objects and each car you pass it through can do something to each object until you reach the end.
PowerShell Profile
This is basically the ability to customize your PowerShell session each time you open or start PowerShell. You can do things such as pre-load modules, create custom bits of PowerShell code for reuse or easy access, and many other things. I would compare this to your profile in Windows that keeps up with things like the icons or applications you have pinned to the taskbar or the default browser.

Now I want to take you through a few core cmdlets that are used most commonly to discover what is available in the current version of PowerShell or the module you might be working with in it. I tend to use these commands almost every time I open PowerShell. I do not try to memorize everything, especially when I can look it up so quickly in PowerShell.

Get-Command

This cmdlet does exactly what you think it does, gets a list of commands that are available in your current PowerShell session. You can use the parameters of this cmdlet to filter the list down to what interest you, say all the “get” cmdlets:

Get-Command -Verb Get -CommandType Cmdlet

Get-Help

Now you might be wondering where the documentation is for all of the cmdlets you saw using Get-Command? Where is the Books Online equivalent to what you get with SQL Server? Well unlike SQL Server you can actually get the documentation via the cmdlet Get-Help. This cmdlet can return the information to you or you can use a parameter to open it up in the browser, if it is available. So for example one of the best things to look up documentation on initially is the Get-Help cmdlet itself:

Get-Help

The output of this command is good to read through but the main items I want to pull out are three particular parameters:

Online: This will take you to the TechNet page of the documentation for the cmdlet. This may not work with every cmdlet you come across but if Microsoft owns it there should be something.
Examples: This is going to provide a few examples and descriptions of how you can use the cmdlet and the more common parameters.
Full: This will show you pretty much what document is online. This just keeps you in PowerShell instead of view it in the browser.

So let me try bringing up the examples of the Get-Help cmdlet itself:

Get-Help Get-Help -Examples

If you are using Windows 7 OS or higher, you may receive something similar to this screenshot. This is something that was added in PowerShell version 3.0, the cmdlet Update-Help. This cmdlet is used to actually update the help files on a computer as needed. In the event Microsoft updates the help files, or the online TechNet page, you can use this to download a current version of it. Microsoft has moved to this method in place of trying to do the updates locally with cumulative updates or service packs. It does require Internet access to execute the cmdlet. If your machine is not on the Internet you can download them from Microsoft’s download center. In order to fix the above message I just need to issue the command: Update-Help.

You should see a progress bar as shown below while it is running through updating all the files (which that progress bar is actually done using PowerShell):

I ended up getting two errors for certain modules and this is because I am not running the cmdlet with elevated privileges. If you open PowerShell.exe with the “Run As Administrator” option and then execute the cmdlet again it will be able to update all help files without error.

Now if you run the previous command again you should see the actual examples, although if you notice it can be annoying to try and scroll back up to read all that information. A tidbit I did not know about right away was that there is a parameter in Get-Help that opens up a separate window, which makes it easier to read called, “-ShowWindow“. It is basically the “-Full” output but with the option to filter out sections that do not interest you.

Get-Help Get-Help -ShowWindow

You actually can use Get-Help to search for cmdlets as well. I tend to do this more than trying to use Get-Command just because it is a bit quicker. You can just issue something like this to find all the “Get” cmdlets:

Get-Help get*

One more thing about the help system in PowerShell, it also includes things called “about files” that are basically concept topics that go deeper into certain areas. They offer a wealth of information and you can also get to these online. Something for you to try on your own to see what is available is just issue this command:

Get-Help about*

Get-Member

This cmdlet is a little gem that you will use more than anything. If you pipe any cmdlet (or one-liner) to Get-Member it will provide you a list of the properties or methods available to you for the object(s) passed. This cmdlet also includes a filter of “-MemberType” that I can use to only return the properties available to me. The properties are those that we can “select” to return as output or pass to other cmdlets down the pipe.

Get-Command | Get-Member -MemberType Property

Out-GridView

I am only going to touch on this cmdlet. It can be used to output objects into a table like view, that also offers some filtering attributes too. There are a few different Out-* cmdlets that are available to you for outputting information to various destinations. You can find these using the Get-Command or Get-Help cmdlets. To use Out-GridView on a Windows Server OS you will have to add the PowerShell ISE feature. You will get an error stating as much if you do not.

Get-Command | Out-GridView

Summary

The three cmdlets Get-Command, Get-Help, and Get-Member that I spoke on above are ones I think you should become very familiar with and explore them deeply. Once you master using these it will provide you the ability to find out anything and everything about a cmdlet or module that you are trying to use. When you start working with various modules such as Azure or SQL Server PowerShell (SQLPS) these cmdlets are quite useful in discovering what is available.