Over the past months, I’ve devoted a lot of time to scripts and tips on using Powershell. While helpful, these articles assume a level of familiarity with Powershell that a lot of SQL Server administrators don’t have. I wanted to take some time to help out those who are looking for a place to start.
The great thing about Powershell is that the Microsoft team has put a lot of effort into building cmdlets that allow you to discover how to use the language. The term ‘cmdlets’ was invented by the Powershell team to help make the language distinct, but they’re essentially functions. Three cmdlets, in particular, will help teach you the language and discover how you can use it:
I like to refer to these cmdlets with the mildly cheesy name “The Holy Trinity of Powershell Self Discovery”. Yes, that’s a mouthful. With such a clunky name, though, it is hard to forget about them. Because of the information they provide, not a day goes by where I use one of these cmdlets while working with Powershell.
The first of these three, Get-Command, is the cmdlet that lets you browse the cmdlet ‘directory’. While there are several arguments we can pass to this cmdlet, really all you should concern yourself with at the beginning is passing wildcard searches for cmdlets you might be looking for. If you keep in mind that there’s a defined list of Powershell verbs, Get-Command becomes a good way to find cmdlets.
For example, let’s say we wanted to find a cmdlets to add a Windows firewall rule. The best way to start is to simple filter all the cmdlets containing the word “firewall”:
Quickly, you’ll get a list of 30 functions for manipulating different parts of the firewall. A lot easier to read that the full list of 1000+ Powershell cmdlets. But we want to filter our list down even more, so let’s improve our filter. Since we know we want a new rule, we can improve our wildcard search:
Our result is a single cmdlet, New-NetFirewallRule. Remember that anytime we create something in Powershell, the standard syntax will be “New-” and the noun. We add this into our wildcard search, plus the word “rule” to further filter down. Combine this all into how we use Get-Command, and we have a powerful way to search the language.
Once you find your cmdlet, though, how do you learn how to use it? Fortunately for us, the Powershell team took a page from the *nix world. For anyone who as worked in Unix or Linux, you’ve probably made heavy use of the ‘man’ pages. This is a built in help system to help describe shell commands. Powershell has its own system and you access it using Get-Help (conveniently aliased in Powershell as ‘man’).
Using our previous example, let’s learn about the New-NetFirewallRule cmdlet. The syntax is easy enough:
Running this will output text to the host window that describes the cmdlet. By default, we’ll see a synopsis, a description, and an outline of the parameters the cmdlet accepts. Extremely useful, but this is just scratching the surface. Get-Help will also accept additional arguments that can give you even more detail or functionality if you want it:
- -Examples – Examples of how the cmdlet gets used
- -Detailed – Even more information on how the cmdlet functions
- -Full – The entire help file for the cmdlet in question
- -ShowWindow – Output the full help file to a separate windows
- -Online – Open up the TechNet page for the cmdlet
But wait, there’s more! Two more awesome things about the Powershell help system are that you can find help on more than just cmdlets and it is constantly updated. Powershell contains a list of topics that you can read on to see how to use the language. These are all found with the text “about_” and you can get a listing of these using:
If you want to learn more about how to use variables, for example, you can look at the about_Variables topic and read the specifics about using Powershell variables. There are over 100 different topics in the help system for Powershell 4.0, baking your learning right into the language.
Of course, this information can change and update frequently. In order to keep pace with this rate of change, the Powershell team separated the help system from your standard Windows updates and made manageable online. This means if you ever think your help system is out of date, you only have to run the Update-Help cmdlet when connected to the internet and your local help system will get all the current information.
One of the strongest advantages of Powershell is that it is built on .Net. This means that everything in Powershell is a .Net object. To explore these objects and what they have to offer, you can use the Get-Member cmdlet to provide information about a cmdlet.
The use is pretty simple. Take your variable and pass it via the pipeline to Get-Member:
[string]$AString = ‘Tea. Earl Grey. Hot.’ $AString | Get-Member
What will follow is a list of the object type, methods, and properties you can leverage with that object. You get a comprehensive view of all the capabilities of the object.
If we go back a few posts, you can read how I compared sqlcmd with Invoke-SqlCmd. Get-Member was key to this comparison, because it allowed me to explore the outputs of both:
$query = ‘SELECT type,count(1) FROM sys.objects GROUP BY type;’ $cmdout = sqlcmd -Q $query $invout = Invoke-Sqlcmd -Query $query $cmdout | Get-Member $invout | Get-Member
Comparing these two outputs shows us a lot about the difference between the two commands. We can see that the sqlcmd output is an array of System.Strings and Invoke-SqlCmd is a collection of System.Data.Datarow. For more on the importance of this difference, read my other blog post. The key is to understand how you can explore and discover this difference using Get-Member.
A Compass and a Map
Understanding Powershell is a long road. There’s a lot of depth to it, providing a great deal of functionality. It can be easy to get lost in the details. While we live in the day and age of LMGTFY, it still helps to have some basic tools at our disposal to find our way through something new. Get-Command, Get-Help, and Get-Member are three cmdlets you will always have access to, helping you find your way to solving problems in Powershell.