$Variable

All variables in PowerShell start with a $ symbol

A variable is a place to store data. It’s a box with a label on it. Let’s say you have a list of 400 users with their names, email addresses, job titles etc. You can just put it in a variable called $userlist, and then just use the variable name when you need to access it, or perform some process with it.

#Putting something in a variable
$variable = 50

#Checking what is in a variable
$variable

There’s a slightly longer way to do this, using Cmdlets for a declaring variables:

Set-Variable -Name Colour -Value "blue"

Get-Variable -Name Colour

You’ll notice that this way you don’t have to use the $ to set or read the variable.

Pre-defined Variables

PowerShell does have some variables that it itself uses while running. Some of these will be session-based, and some will be based on the environment you are in.

Here are some examples.

Version information for the shell itself:

$PSVersiontable

Nothing

The $null variable represents nothing, assigning $null to something will let you create a variable that does not store anything. This is also a fairly nuanced topic, I may have just straight up lied in the sentence before this to cut through some noise. As you gain more experience you should understand what $null means and how it is not truly ‘nothing’.

$thisIsNothing = $null

$thisIsNothing

No Output, because no thing.

It is highly useful for checking if a variable is empty (IF Statements):

Set-Variable -Name empty

$notEmpty = 4

if ($null -eq $empty){
	Write-Output '$empty is null'
}

if ($null -eq $notempty){
	Write-Output '$notEmpty is null'
}

True or False

Another pre-set couple of variables are $true and $false you cannot change these, these are used to represent a single-bit value, i.e. a 1 or 0 in memory. They are called Booleans because of a guy called George Boole, more on these in Data Structures.

$Mary = @{
	hasAnOrange = $true
	hasABanana = $false
}

if ($Mary.hasAnOrange) {
	Write-Output "Mary has an orange."
}

if ($Mary.hasABanana) {
	Write-Output "Mary has a Banana."
}

One value is true, the other is set to false, only the true one will run.

Variables inside variables

Don’t exist.

By equating one variable to another, you will simply copy the data from the variable on the right side of the = to the left.

$variable_one = 10

$variable_two = $variable_one

$variable_two

Small note: this requires a little clarification, as this behaviour is only true for value types, but not references.