My First PowerShell

19 July 2017

PowerShell ISE

A guide to the bits that I needed when starting to use PowerShell, particularly in the context of Azure. Not a complete guide to PowerShell :) For that, try these:

Environment

For my experiments, I’m using the PowerShell ISE. Just hit the Windows key, type ‘ise’ and it will come up.

ISE Tips:

Open your first code editor tab with Ctrl+N
Switch to the terminal (blue part) by clicking in it or pressing Ctrl+D
Switch to the editor (white part) by pressing Ctrl+I
Run the content of the editor with F5
Run just the selected content of the editor with F8

Variables and printing to terminal

You can print out text (string literals) with either single or double quotes, no cmdlet needed:

'Hello'
"Goodbye"

Hello
Goodbye

The difference is that double quotes are dynamic - they expand embedded variables (like in PHP). Here’s how to define a variable and print it within another string:

$myName = "Ste"
'Hey $myName'
"Hey $myName"

Hey $myName
Hey Ste

Note that the double quotes expand the variable but the single quotes don’t. There are more methods than these for string handling, you can find a good overview in this Scripting Guy blog post, Use PowerShell to Glue Strings Together.

You can store the result of a cmdlet in a variable but you don’t have to. Without a variable, the cmdlet will dump its result to the screen. With a variable, it won’t print out the result until you manually echo the content of the variable.

$rg = New-AzureRmResourceGroup -Name '20533-Ste' -Location 'north europe'
$rg

ResourceGroupName : 20533-Ste
Location          : northeurope
ProvisioningState : Succeeded
Tags              : 
ResourceId        : /subscriptions/022db750-...-6e1be5c4a6ae/resourceGroups/20533-Ste

I think the formatting Name : Value represents the properties of an object (but I’m not 100% sure).

Error handling

You can do try-catch blocks just like in C#. In the example below, Fake-Cmdlet will fail, so “Hello World” is never printed:

"--------"
try {
	Fake-Cmdlet
	"Hello World"
}
catch { "An error occurred" }


--------
An error occurred

Hash Tables

Lots of cmdlets return hash tables (don’t be scared - that’s just an unsorted collection of key-value pairs). You can create your own and pass them as parameters to certain cmdlets. @ indicates a hash table. Contents goes in braces {}, pairs are separated by a semicolon ; (not a comma as you might expect). Btw, you are allowed dangling semicolons at the end of the list of properties.

$myObj = @{ name = 'Smurfs'; platform = 'Atari 2600'}

Print it out:

$myObj

Name        Value                                                                              
----        -----                                                                              
name        Smurfs                                                                             
platform    Atari 2600

Other uses of @

The @ operator can be used for a couple of other nifty uses, including as the ‘SPLAT’ operator, beyond the scope of this little guide. Check out this SO Answer about using the @ operator in PowerShell

Hash tables and Azure cmdlets

Hash tables are used for Tags on an Azure Resource Groups and Resources. I can create a tag reason=training on my existing resource group by identifying it by name and changing the Tag parameter:

Set-AzureRmResourceGroup -Name '20533-Ste' -Tag @{ reason = 'training' }

(I could also have just passed a -Tag parameter to the original New-AzureRmResourceGroup call)

We can pass in a pre-existing hash table variable. The collection of tags you pass to -Tag overwrites the whole existing collection.

$tags = @{ reason = 'training'; herolevel = '>9000'; }
Set-AzureRmResourceGroup -Name '20533-Ste' -Tag $tags

SteGriff

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