PowerShell Do Whereas Loop Defined — LazyAdmin

Loops are one of many fundamental capabilities in any programming or scripting language. A type of loops is the Do Whereas loop, which executes a chunk of code whereas the situation is true.

In PowerShell, we will use a Whereas loop and a Do-Whereas loop. They could look the identical, however they do have a distinction that’s necessary to know.

On this article, I’ll clarify the distinction between the 2 loops and present the best way to use the Do-Whereas Loop in your script.

PowerShell Do Whereas Loop

When writing a script you generally must execute a chunk of code an x period of time till a situation is met. We will do that with a loop which is without doubt one of the management circulate statements that we will use.

Now in PowerShell, we even have three completely different Loop sorts that we will use:

• Whereas Loop
• Do Whereas Loop
• Do Till Loop

The Whereas loop will solely execute the code contained in the loop if the situation is true. The Do Whereas and Do Till, nevertheless, will execute the code within the loop at the least as soon as. This is a crucial distinction to remember.

The distinction between Do-Whereas and Do-Till is that the primary will execute the code within the loop so long as the situation is true. Whereas Do-Till we execute the code so long as the situation is fake.

Additionally good to know is that PowerShell gained’t proceed with the execution of your script till the loop is accomplished.

Utilizing the Do-Whereas Loop

To make use of the Do-Whereas loop inside our scripts, we might want to outline the code that’s going to be executed within the Do half and add a situation within the Whereas half.

Let’s check out a easy instance. The code under will write the present quantity ($i), and add 1 to it, so long as $i is lower than 5:

$i = 0
do {
    # code to execute
    Write-Host "The quantity is $i"
    $i++
} whereas ($i -le 5)

Check out the instance above, merely copy and paste it into Home windows Terminal. You will note that the code is being executed whereas the situation is true.

Proceed and Break

When working with loops in PowerShell, we will use Proceed and Break to regulate, or intrude with, the circulate of the loop. When the Break assertion is encountered inside a loop, then the script jumps out of the loop and continues under the loop with the subsequent line of code. That is carried out whatever the situation that’s specified within the Whereas assertion.

Proceed, alternatively, will cease processing the present merchandise within the loop, and soar to the subsequent iteration. The proceed assertion will re-evaluate the whereas situation. So if the situation is met earlier than the proceed assertion, then the Do-Whereas loop is completed.

Let’s check out a Proceed instance inside a loop. The code under will get all of the recordsdata from the given listing. If we discover a hidden file, then the Proceed assertion is triggered, making it go to the subsequent one:

$recordsdata = Get-ChildItem "C:Temp"
$i = 0

Do {
    $file = $recordsdata[$i]
    
    if ($file.Attributes -match "Hidden") {
        $i++
        proceed  # Skip hidden recordsdata
    }

    Write-Host "Processing file: $file.Title"
    $i++
} Whereas ($i -lt $recordsdata.Rely)

The Break assertion can for instance be used to examine if we nonetheless wish to proceed with the loop. The instance under will ask the consumer in the event that they wish to proceed, and if the reply is not any, we’ll exit the loop:

Do {
    $response = Learn-Host "Do you wish to proceed? (sure/no)"
    
    if ($response -eq "no") {
        Write-Host "Exiting loop."
        break  # Exit the loop if the consumer chooses "no"
    }
    
    Write-Host "Persevering with..."
    
} Whereas ($response -ne "no")

Write-Host "Loop ended."

Do-Whereas Examples

Personally, I discover it simpler to study programming or scripting with examples. So I’ve created a few real looking Do-Whereas examples to get you began.

The primary one we’re going to try is a small script that can wait till the required service is working. On this instance, we’re going to wait till the Home windows Replace Service is working. Needless to say PowerShell gained’t execute the code under the Do Whereas loop till the Whereas situation is met:

$serviceName = "wuauserv"  # Home windows Replace service
$serviceStatus = (Get-Service -Title $serviceName).Standing

Do {
    Write-Host "Ready for the service '$serviceName' to start out..."
    Begin-Sleep -Seconds 5
    $serviceStatus = (Get-Service -Title $serviceName).Standing
} Whereas ($serviceStatus -ne "Operating")

Write-Host "The service '$serviceName' is now working."

For the instance above, you’d truly begin with an If-Else assertion, checking if the service is working in any respect or not. If the service is just not working, you can begin it, after which use the code above to attend till it’s up and working.

Validating Person Enter

One other widespread use case is when you should validate a consumer enter in your script. We will use the Do-Whereas loop to maintain asking for brand new enter till it matches our outlined situation. For instance, we ask for an electronic mail handle, and can examine if it matches the e-mail handle sample earlier than we proceed:

$emailPattern = "^[w.-]+@[w.-]+.w+$"
$electronic mail = ""

Do {
    $electronic mail = Learn-Host "Enter a legitimate electronic mail handle"
} Whereas ($electronic mail -notmatch $emailPattern)

Write-Host "Legitimate electronic mail entered: $electronic mail"

Within the Whereas situation, we aren’t restricted to at least one situation. We will have a number of circumstances and mix them utilizing the -And or -Or operators. So for instance, we will set a max underneath the variety of guesses as consumer could make:

$maxAttempts = 3
$makes an attempt = 0
do {
    $enter = Learn-Host "Enter a quantity between 1 and 10"
    $makes an attempt++
} whereas (($enter -lt 1 -or $enter -gt 10) -and ($makes an attempt -ne $maxAttempts))

Infinite Loop

For those who set the situation to true, then you’ll be able to create an infinite loop in PowerShell. The code contained in the loop will probably be executed till the $situation contained in the loop is true. Then we will use the Break assertion to exit the loop.

Do {
    # Do stuff perpetually
    Write-Host 'looping'

    # Use Break to exit the loop
    If ($situation) {
        Break
    }
} Whereas ($true)

Obtain File Try

Do-while loops are additionally a fantastic possibility if you wish to attempt one thing. Within the instance under, we’ll attempt to obtain a file. Utilizing a Attempt-Catch block, we will examine if the obtain try was profitable or not.

We are going to hold attempting to obtain the file till it’s profitable or the utmost makes an attempt are reached.

$url = "https://instance.com/file.zip"
$vacation spot = "C:Downloadsfile.zip"
$try = 0
$maxAttempts = 5

Do {
    $try++
    Write-Host "Try $try: Downloading file..."
    attempt {
        Invoke-WebRequest -Uri $url -OutFile $vacation spot
        $success = $true
    } catch {
        Write-Host "Obtain failed, retrying..."
        Begin-Sleep -Seconds 5
        $success = $false
    }
} Whereas (-not $success -and $try -lt $maxAttempts)

if ($success) {
    Write-Host "File downloaded efficiently!"
} else {
    Write-Host "Didn't obtain file after $maxAttempts makes an attempt."
}

Wrapping Up

Do-Whereas loops are a fantastic management circulate assertion to make use of in PowerShell. Needless to say the code contained in the Do loop is at all times executed at the least one time. For those who solely wish to execute the code when the situation is met, you will have to make use of the traditional Whereas loop.

If you wish to study extra about PowerShell, then be sure you try the different PowerShell articles and naturally the Cheat Sheet. And if in case you have any questions, simply drop a remark under.