If this then that

A basic building block of most programming languages is the ‘if’ statement. Its general formula goes like this:

If some condition is met (it’s true), do something.

In PowerShell this is achieved with this syntax:

$IAmBusy = $true
$IAmHungry = $false

if ($IAmBusy) {
	Write-Output "I'll call you later, I see you are busy."
}

if ($IAmHungry) {
	Write-Output "Let's go get some food"
}

if checks for the expression between the () brackets, if it resolves to a true statement, it will run the code between the {} brackets.

Since the values above were defined as $true and $false directly, (Data Structures for more info on what those are). It’s easy to see why each statement ran.

Let’s calculate inside ()

This time, let’s calculate whether the condition is true.

if (2+2 -eq 4) {
	Write-Output "2 plus 2 is 4!!!"
}

This ran the code, and the reason for that is:

2+2 -eq 4

The condition outputs a $true or $false when executed. So we can only make conditions based on this logic, so we could not write:

if (2+2 = 4) {
	Write-Output "You've done something wrong!"
}

Because it will fail.

So here’s this:

if (2) {
	Write-Host "Wait. What?"
}

I recommend looking online why this works, I only have so much free time to write these.

How expressions inside () are evaluated

Comparison and Logical Operators

Or Else

So we can test for IF something is true, but what if it comes up false, and we want to do something else?

$Colour = "blue"

if ($colour -eq "gray") {
	Write-Output "You've found my favourite colour!"
} else {
	Write-Output "No, $Colour is not my favourite colour."
}

Easy enough, but what if we want to do some more if checks. Since else {} statement will run every single time that the IF conditions comes up false, we can’t really create backups. Or at least not cleanly. So for this reason we have elseif.

$testResults = "We failed main check 1, but passed fallback check 2"

if ($testResults -like "*passed main check 1*") {
	Write-Output "we passed check 1!"
} elseif ($testResults -like "*passed fallback check 2*") {
	Write-Output "fallback test 2 succeeded, phew..."
} else {
	Write-Output "We're going down captain!"
}

However, in my personal opinion you should avoid this. If you want to your script to run a different process based on mutliple conditions, please have a look at and attempt to use switch statements instead.