Mastering PowerShell for Windows System Administration: ForEach, For, If-Else, Switch, and While Loops

PowerShell is a powerful scripting language designed specifically for Windows system administration. It provides a robust framework for automating repetitive tasks, managing servers, and streamlining IT workflows. In this blog, we will explore practical PowerShell scripts that leverage ForEach, For, If-Else, Switch, and While loops to handle common administrative tasks. These examples are perfect for both beginners and seasoned admins looking to sharpen their scripting skills.

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Why Use PowerShell for Windows Administration?

PowerShell is ideal for managing Windows environments because it:

Provides direct access to the Windows Management Instrumentation (WMI) and .NET classes.
Supports advanced automation through scripts and functions.
Integrates seamlessly with Active Directory and Azure.
Allows for powerful task automation using loops and conditionals.

1. Disk Space Monitoring (ForEach and If-Else)

Checking the free space on multiple drives is a routine task for system administrators. This script iterates through each drive on a server, reporting available space:

$drives = Get-PSDrive -PSProvider FileSystem

foreach ($drive in $drives) {

    $freeSpaceGB = [math]::Round($drive.Free / 1GB, 2)

    if ($freeSpaceGB -lt 10) {

        Write-Output "Warning: Drive $($drive.Name) is low on space ($freeSpaceGB GB free)."

    } else {

        Write-Output "Drive $($drive.Name) is healthy with $freeSpaceGB GB free."

    }

}

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$drives = Get-PSDrive -PSProvider FileSystem

foreach ($drive in $drives) {

$freeSpaceGB = [math]::Round($drive.Free / 1GB, 2)

if ($freeSpaceGB -lt 10) {

Write-Output "Warning: Drive $($drive.Name) is low on space ($freeSpaceGB GB free)."

} else {

Write-Output "Drive $($drive.Name) is healthy with $freeSpaceGB GB free."

}

2. Network Latency Checker (ForEach and For)

Maintaining a healthy network is crucial. This script tests the average latency to each server, identifying potential connectivity issues:

$servers = @("Server1", "Server2", "Server3")

$pingCount = 5

foreach ($server in $servers) {

    $totalTime = 0

    for ($i = 1; $i -le $pingCount; $i++) {

        $ping = Test-Connection -ComputerName $server -Count 1 -Quiet

        if ($ping) {

            $response = Test-Connection -ComputerName $server -Count 1

            $totalTime += $response.ResponseTime

        }

    }

    if ($totalTime -gt 0) {

        $averageTime = [math]::Round($totalTime / $pingCount, 2)

        Write-Output "Average ping time to $server is $averageTime ms."

    } else {

        Write-Output "$server is offline."

    }

}

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$servers = @("Server1", "Server2", "Server3")

$pingCount = 5

foreach ($server in $servers) {

$totalTime = 0

for ($i = 1; $i -le $pingCount; $i++) {

$ping = Test-Connection -ComputerName $server -Count 1 -Quiet

if ($ping) {

$response = Test-Connection -ComputerName $server -Count 1

$totalTime += $response.ResponseTime

}

if ($totalTime -gt 0) {

$averageTime = [math]::Round($totalTime / $pingCount, 2)

Write-Output "Average ping time to $server is $averageTime ms."

} else {

Write-Output "$server is offline."

}

3. Bulk User Account Creation (ForEach and If-Else)

Creating multiple user accounts is a common task, especially during employee onboarding. This script automates the process:

$usernames = @("User1", "User2", "User3")

$password = ConvertTo-SecureString "P@ssw0rd123" -AsPlainText -Force

foreach ($username in $usernames) {

    if (!(Get-LocalUser -Name $username -ErrorAction SilentlyContinue)) {

        New-LocalUser -Name $username -Password $password -FullName "$username Account" -Description "Standard user account"

        Write-Output "Created user account: $username"

    } else {

        Write-Output "User account $username already exists."

    }

}

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$usernames = @("User1", "User2", "User3")

$password = ConvertTo-SecureString "P@ssw0rd123" -AsPlainText -Force

foreach ($username in $usernames) {

if (!(Get-LocalUser -Name $username -ErrorAction SilentlyContinue)) {

New-LocalUser -Name $username -Password $password -FullName "$username Account" -Description "Standard user account"

Write-Output "Created user account: $username"

} else {

Write-Output "User account $username already exists."

}

4. Log File Cleanup (ForEach, For, and If-Else)

Old log files can quickly consume disk space. This script removes logs older than 30 days from multiple directories:

$directories = @("C:\Logs\App1", "C:\Logs\App2", "C:\Logs\App3")

$daysOld = 30

foreach ($directory in $directories) {

    $files = Get-ChildItem -Path $directory -Filter "*.log"

    for ($i = 0; $i -lt $files.Count; $i++) {

        if ($files[$i].LastWriteTime -lt (Get-Date).AddDays(-$daysOld)) {

            Remove-Item -Path $files[$i].FullName -Force

            Write-Output "Deleted: $($files[$i].FullName)"

        }

    }

}

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$directories = @("C:\Logs\App1", "C:\Logs\App2", "C:\Logs\App3")

$daysOld = 30

foreach ($directory in $directories) {

$files = Get-ChildItem -Path $directory -Filter "*.log"

for ($i = 0; $i -lt $files.Count; $i++) {

if ($files[$i].LastWriteTime -lt (Get-Date).AddDays(-$daysOld)) {

Remove-Item -Path $files[$i].FullName -Force

Write-Output "Deleted: $($files[$i].FullName)"

}

5. Service Status Checker (ForEach, For, and If-Else)

This script checks the status of a specific service on multiple servers, ensuring critical services are always running:

$servers = @("Server1", "Server2", "Server3")

$serviceName = "W32Time"

foreach ($server in $servers) {

    try {

        $services = Get-Service -ComputerName $server -Name $serviceName

        for ($i = 0; $i -lt $services.Count; $i++) {

            if ($services[$i].Status -eq "Running") {

                Write-Output "$($services[$i].DisplayName) on $server is running."

            } else {

                Write-Output "$($services[$i].DisplayName) on $server is not running."

            }

        }

    }

    catch {

        Write-Output "Unable to connect to $server."

    }

}

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$servers = @("Server1", "Server2", "Server3")

$serviceName = "W32Time"

foreach ($server in $servers) {

try {

$services = Get-Service -ComputerName $server -Name $serviceName

for ($i = 0; $i -lt $services.Count; $i++) {

if ($services[$i].Status -eq "Running") {

Write-Output "$($services[$i].DisplayName) on $server is running."

} else {

Write-Output "$($services[$i].DisplayName) on $server is not running."

}

catch {

Write-Output "Unable to connect to $server."

}

6. Directory Size Checker (While)

Monitors the size of a directory, sending alerts if it exceeds a threshold:

$directory = "C:\Logs"

$thresholdGB = 5

 

while ($true) {

    $sizeGB = (Get-ChildItem -Path $directory -Recurse | Measure-Object Length -Sum).Sum / 1GB

    if ($sizeGB -gt $thresholdGB) {

        Write-Output "Warning: Directory $directory is over $thresholdGB GB."

        break

    }

    Start-Sleep -Seconds 60

}

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$directory = "C:\Logs"

$thresholdGB = 5

while ($true) {

$sizeGB = (Get-ChildItem -Path $directory -Recurse | Measure-Object Length -Sum).Sum / 1GB

if ($sizeGB -gt $thresholdGB) {

Write-Output "Warning: Directory $directory is over $thresholdGB GB."

break

}

Start-Sleep -Seconds 60

}

7. System Uptime Checker (Switch)

This script uses a switch statement to categorize server uptime:

$uptime = (Get-CimInstance Win32_OperatingSystem).LastBootUpTime

$daysUp = (New-TimeSpan -Start $uptime -End (Get-Date)).Days

switch ($daysUp) {

    {$_ -lt 7} { Write-Output "Server recently rebooted ($daysUp days up)." }

    {$_ -lt 30} { Write-Output "Server is stable ($daysUp days up)." }

    default { Write-Output "Server is highly stable ($daysUp days up)." }

}

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$uptime = (Get-CimInstance Win32_OperatingSystem).LastBootUpTime

$daysUp = (New-TimeSpan -Start $uptime -End (Get-Date)).Days

switch ($daysUp) {

{$_ -lt 7} { Write-Output "Server recently rebooted ($daysUp days up)." }

{$_ -lt 30} { Write-Output "Server is stable ($daysUp days up)." }

default { Write-Output "Server is highly stable ($daysUp days up)." }

}

Conclusion

Mastering these PowerShell loops and conditionals can significantly enhance your Windows system administration skills. From automating routine maintenance to managing complex server environments, these examples demonstrate the power and flexibility of PowerShell. With practice, you’ll find yourself building even more sophisticated scripts that reduce manual effort, improve efficiency, and ensure the smooth operation of your IT infrastructure. Keep experimenting and expanding your PowerShell toolkit to stay ahead in the world of Windows administration.

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