PowerShell Scripting

Comprehensive reference for building PowerShell scripts for Windows automation and system administration.

Target: Windows PowerShell 5.1 and PowerShell 7.x (cross-platform)

When to Use This Skill

•Building automation scripts for Windows systems
•Managing Windows services, processes, and scheduled tasks
•Working with files, folders, and registry operations
•Creating reusable functions and modules
•System administration tasks (users, groups, permissions)
•Automating repetitive administrative tasks
•Migrating bash/shell scripts to Windows equivalents

Prerequisites

PowerShell Versions

Version	Platform	Notes
Windows PowerShell 5.1	Windows only	Pre-installed on Windows 10/11, Server 2016+
PowerShell 7.x	Cross-platform	Install separately, runs alongside 5.1

Check Version

powershell

$PSVersionTable.PSVersion

Execution Policy

Scripts require appropriate execution policy:

powershell

# Check current policy
Get-ExecutionPolicy

# Set policy (run as Administrator)
Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope CurrentUser

Policy	Description
`Restricted`	No scripts allowed (Windows default)
`RemoteSigned`	Local scripts run; downloaded scripts need signature
`Unrestricted`	All scripts run with warning for downloaded

Core Concepts

Cmdlet Naming Convention

PowerShell uses Verb-Noun naming:

code

Get-Process      # Retrieves process information
Stop-Service     # Stops a service
New-Item         # Creates a new item
Set-Location     # Changes current location

Common Verbs:

Verb	Use For	Example
`Get`	Retrieve data	`Get-Service`, `Get-ChildItem`
`Set`	Modify existing	`Set-Content`, `Set-Variable`
`New`	Create new	`New-Item`, `New-Object`
`Remove`	Delete	`Remove-Item`, `Remove-Variable`
`Start`	Begin operation	`Start-Process`, `Start-Service`
`Stop`	End operation	`Stop-Process`, `Stop-Service`
`Test`	Verify/check	`Test-Path`, `Test-Connection`
`Invoke`	Execute action	`Invoke-Command`, `Invoke-WebRequest`

Discovery Commands

powershell

# Find all approved verbs
Get-Verb | Sort-Object Verb

# Find commands by verb
Get-Command -Verb Get

# Find commands by noun
Get-Command -Noun Service

# Find commands in a module
Get-Command -Module ActiveDirectory

# Get detailed help
Get-Help Get-Process -Full

# Get examples only
Get-Help Get-Process -Examples

# Discover object properties and methods
Get-Service | Get-Member

The Pipeline

PowerShell passes objects (not text) through the pipeline:

powershell

# Chain commands with |
Get-Service | Where-Object Status -eq 'Running' | Select-Object Name, Status

# Filter early (filter left)
Get-Service -Name w* | Where-Object Status -eq 'Running'

# Format output
Get-Process | Sort-Object CPU -Descending | Select-Object -First 10

Pipeline Best Practices:

•Filter as early as possible ("filter left")
•Use native parameters before Where-Object
•Objects maintain type information through pipeline

Variables and Data Types

Variable Basics

powershell

# Assign variable
$name = "Server01"

# Multiple assignment
$a, $b, $c = 1, 2, 3

# Typed variable
[string]$message = "Hello"
[int]$count = 42
[datetime]$date = Get-Date

# Environment variables
$env:COMPUTERNAME
$env:USERNAME
$env:PATH

Common Data Types

powershell

[string]    # Text
[int]       # Integer
[double]    # Decimal number
[bool]      # $true or $false
[array]     # Collection
[hashtable] # Key-value pairs
[datetime]  # Date and time

Arrays and Collections

powershell

# Array
$servers = @("Server01", "Server02", "Server03")
$servers[0]           # First element
$servers[-1]          # Last element
$servers += "Server04" # Add element

# Hashtable
$config = @{
    Name = "MyApp"
    Version = "1.0"
    Enabled = $true
}
$config.Name          # Access by key
$config["Version"]    # Alternative syntax

String Operations

powershell

# String interpolation (double quotes)
$name = "World"
"Hello, $name!"       # Hello, World!

# Literal string (single quotes)
'Hello, $name!'       # Hello, $name!

# Subexpressions
"Date: $(Get-Date -Format 'yyyy-MM-dd')"

# Here-strings (multiline)
$script = @"
Line 1
Line 2 with $variable
"@

# String methods
$text = "PowerShell"
$text.ToUpper()       # POWERSHELL
$text.Length          # 10
$text.Contains("Shell") # True
$text.Replace("Shell", "Script")

Control Flow

Conditionals

powershell

# If/ElseIf/Else
if ($value -gt 10) {
    "Greater than 10"
} elseif ($value -eq 10) {
    "Equal to 10"
} else {
    "Less than 10"
}

# Switch statement
switch ($status) {
    "Running" { "Service is running" }
    "Stopped" { "Service is stopped" }
    default   { "Unknown status" }
}

# Ternary operator (PowerShell 7+)
$result = $value -gt 10 ? "High" : "Low"

Comparison Operators

Operator	Description	Example
`-eq`	Equal	`$a -eq $b`
`-ne`	Not equal	`$a -ne $b`
`-gt`	Greater than	`$a -gt 10`
`-lt`	Less than	`$a -lt 10`
`-ge`	Greater or equal	`$a -ge 10`
`-le`	Less or equal	`$a -le 10`
`-like`	Wildcard match	`$name -like "*.txt"`
`-match`	Regex match	`$text -match "\d+"`
`-contains`	Collection contains	`$arr -contains "item"`
`-in`	Value in collection	`"item" -in $arr`

Loops

powershell

# ForEach-Object (pipeline)
Get-Service | ForEach-Object { $_.Name }

# foreach statement
foreach ($server in $servers) {
    Test-Connection -ComputerName $server -Count 1
}

# For loop
for ($i = 0; $i -lt 10; $i++) {
    "Iteration $i"
}

# While loop
while ($condition) {
    # code
}

# Do-While / Do-Until
do {
    # code
} while ($condition)

do {
    # code
} until ($condition)

Functions

Basic Function

powershell

function Get-Greeting {
    param (
        [string]$Name = "World"
    )
    
    "Hello, $Name!"
}

Get-Greeting -Name "PowerShell"

Advanced Function

powershell

function Get-SystemInfo {
    <#
    .SYNOPSIS
        Retrieves system information from computers.
    
    .DESCRIPTION
        Gets OS, memory, and CPU information from local or remote computers.
    
    .PARAMETER ComputerName
        The computer(s) to query. Defaults to local computer.
    
    .EXAMPLE
        Get-SystemInfo -ComputerName "Server01"
    
    .EXAMPLE
        "Server01", "Server02" | Get-SystemInfo
    #>
    
    [CmdletBinding()]
    param (
        [Parameter(Mandatory = $false,
                   ValueFromPipeline = $true,
                   ValueFromPipelineByPropertyName = $true)]
        [ValidateNotNullOrEmpty()]
        [string[]]$ComputerName = $env:COMPUTERNAME
    )
    
    process {
        foreach ($computer in $ComputerName) {
            try {
                $os = Get-CimInstance -ClassName Win32_OperatingSystem -ComputerName $computer
                
                [PSCustomObject]@{
                    ComputerName = $computer
                    OSName       = $os.Caption
                    Version      = $os.Version
                    Memory       = [math]::Round($os.TotalVisibleMemorySize / 1MB, 2)
                }
            }
            catch {
                Write-Warning "Failed to query $computer: $_"
            }
        }
    }
}

Parameter Validation

powershell

param (
    [Parameter(Mandatory)]
    [string]$Name,
    
    [ValidateSet("Low", "Medium", "High")]
    [string]$Priority = "Medium",
    
    [ValidateRange(1, 100)]
    [int]$Count = 10,
    
    [ValidateScript({ Test-Path $_ })]
    [string]$Path,
    
    [ValidatePattern("^\d{3}-\d{4}$")]
    [string]$PhoneNumber
)

Error Handling

Try/Catch/Finally

powershell

try {
    # Code that might fail
    $result = Get-Content -Path $filePath -ErrorAction Stop
}
catch [System.IO.FileNotFoundException] {
    Write-Warning "File not found: $filePath"
}
catch {
    # Generic catch
    Write-Error "An error occurred: $_"
    Write-Error $_.Exception.Message
}
finally {
    # Always runs
    # Cleanup code here
}

Error Action Preference

powershell

# For single command
Get-Content -Path "missing.txt" -ErrorAction SilentlyContinue

# For script block
$ErrorActionPreference = "Stop"

Value	Behavior
`Continue`	Display error, continue (default)
`Stop`	Terminate on error
`SilentlyContinue`	Suppress error, continue
`Inquire`	Prompt user

Throw Custom Errors

powershell

if (-not (Test-Path $path)) {
    throw "Path does not exist: $path"
}

Common Operations

File System

powershell

# List items
Get-ChildItem -Path C:\Logs -Recurse -Filter *.log

# Create directory
New-Item -Path C:\Backup -ItemType Directory -Force

# Copy files
Copy-Item -Path C:\Source\* -Destination C:\Backup -Recurse

# Move/Rename
Move-Item -Path C:\Old\file.txt -Destination C:\New\
Rename-Item -Path C:\file.txt -NewName "newname.txt"

# Delete
Remove-Item -Path C:\Temp\* -Recurse -Force

# Read file
$content = Get-Content -Path C:\data.txt
$content = Get-Content -Path C:\data.txt -Raw  # Single string

# Write file
Set-Content -Path C:\output.txt -Value $data
Add-Content -Path C:\log.txt -Value "$(Get-Date): Entry"
$data | Out-File -FilePath C:\output.txt -Encoding UTF8

Services

powershell

# List services
Get-Service | Where-Object Status -eq "Running"

# Service by name
Get-Service -Name "wuauserv"

# Control services (requires elevation)
Start-Service -Name "wuauserv"
Stop-Service -Name "wuauserv"
Restart-Service -Name "wuauserv"

# Set startup type
Set-Service -Name "wuauserv" -StartupType Automatic

Processes

powershell

# List processes
Get-Process | Sort-Object CPU -Descending | Select-Object -First 10

# Start process
Start-Process -FilePath "notepad.exe"
Start-Process -FilePath "cmd.exe" -ArgumentList "/c dir" -Wait -NoNewWindow

# Stop process
Stop-Process -Name "notepad" -Force
Get-Process -Name "notepad" | Stop-Process

Registry

powershell

# Read registry value
Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion"

# Get specific value
(Get-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows NT\CurrentVersion").ProductName

# Set registry value
Set-ItemProperty -Path "HKCU:\Software\MyApp" -Name "Setting" -Value "Value"

# Create registry key
New-Item -Path "HKCU:\Software\MyApp" -Force

# Remove registry key
Remove-Item -Path "HKCU:\Software\MyApp" -Recurse

Network

powershell

# Test connectivity
Test-Connection -ComputerName "server01" -Count 2

# DNS lookup
Resolve-DnsName -Name "example.com"

# HTTP request
Invoke-WebRequest -Uri "https://api.example.com/data" -Method Get
Invoke-RestMethod -Uri "https://api.example.com/data"  # Auto-parses JSON

# Download file
Invoke-WebRequest -Uri $url -OutFile "C:\download.zip"

Scheduled Tasks

powershell

# List tasks
Get-ScheduledTask | Where-Object State -eq "Ready"

# Create task
$action = New-ScheduledTaskAction -Execute "PowerShell.exe" -Argument "-File C:\Scripts\backup.ps1"
$trigger = New-ScheduledTaskTrigger -Daily -At "2:00AM"
Register-ScheduledTask -TaskName "DailyBackup" -Action $action -Trigger $trigger -RunLevel Highest

# Run task
Start-ScheduledTask -TaskName "DailyBackup"

# Remove task
Unregister-ScheduledTask -TaskName "DailyBackup" -Confirm:$false

Event Logs

powershell

# Get recent events
Get-WinEvent -LogName System -MaxEvents 50

# Filter events
Get-WinEvent -FilterHashtable @{
    LogName = 'System'
    Level = 2  # Error
    StartTime = (Get-Date).AddDays(-1)
}

# Write to event log
Write-EventLog -LogName Application -Source "MyScript" -EventId 1000 -Message "Script completed"

Data Formats

JSON

powershell

# Convert to JSON
$data | ConvertTo-Json -Depth 3

# Convert from JSON
$object = Get-Content -Path config.json | ConvertFrom-Json

# API example
$response = Invoke-RestMethod -Uri "https://api.example.com/users"

CSV

powershell

# Export to CSV
Get-Process | Select-Object Name, CPU, WorkingSet | Export-Csv -Path processes.csv -NoTypeInformation

# Import from CSV
$users = Import-Csv -Path users.csv

XML

powershell

# Convert to XML
$data | ConvertTo-Xml

# Read XML
[xml]$config = Get-Content -Path config.xml
$config.root.setting

Script Template

powershell

#Requires -Version 5.1
#Requires -RunAsAdministrator

<#
.SYNOPSIS
    Brief description of script purpose.

.DESCRIPTION
    Detailed description of what the script does.

.PARAMETER Parameter1
    Description of parameter.

.EXAMPLE
    .\Script.ps1 -Parameter1 "Value"
    
    Description of example.

.NOTES
    Author: Your Name
    Version: 1.0
    Date: 2026-02-01
#>

[CmdletBinding()]
param (
    [Parameter(Mandatory)]
    [string]$Parameter1,
    
    [Parameter()]
    [switch]$Force
)

#region Variables
$ErrorActionPreference = "Stop"
$logPath = Join-Path $PSScriptRoot "script.log"
#endregion

#region Functions
function Write-Log {
    param ([string]$Message)
    $timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
    "$timestamp - $Message" | Add-Content -Path $logPath
    Write-Verbose $Message
}
#endregion

#region Main
try {
    Write-Log "Script started"
    
    # Main script logic here
    
    Write-Log "Script completed successfully"
}
catch {
    Write-Log "ERROR: $_"
    throw
}
finally {
    # Cleanup
}
#endregion

Best Practices

Do

•Use approved verbs for function names
•Add comment-based help to functions
•Use [CmdletBinding()] for advanced functions
•Validate parameters early
•Use -ErrorAction Stop with try/catch
•Use single quotes for literal strings
•Filter left in the pipeline
•Use Write-Verbose for debugging output

Avoid

•Hardcoding values (use parameters)
•Using aliases in scripts (gci → Get-ChildItem)
•Modifying global $ErrorActionPreference
•Catching all errors without handling
•Using Write-Host for output (use Write-Output)
•Running scripts as Administrator unnecessarily

Troubleshooting

Issue	Solution
Script won't run	Check `Get-ExecutionPolicy`, set to `RemoteSigned`
Access denied	Run PowerShell as Administrator
Command not found	Check module is imported: `Import-Module ModuleName`
Pipeline returns nothing	Check `Where-Object` filter conditions
Error not caught	Add `-ErrorAction Stop` to command

PowerShell Scripting

When to Use This Skill

Prerequisites

PowerShell Versions

Check Version

Execution Policy

Core Concepts

Cmdlet Naming Convention

Discovery Commands

The Pipeline

Variables and Data Types

Variable Basics

Common Data Types

Arrays and Collections

String Operations

Control Flow

Conditionals

Comparison Operators

Loops

Functions

Basic Function

Advanced Function

Parameter Validation

Error Handling

Try/Catch/Finally

Error Action Preference

Throw Custom Errors

Common Operations

File System

Services

Processes

Registry

Network

Scheduled Tasks

Event Logs

Data Formats

JSON

CSV

XML

Script Template

Best Practices

Do

Avoid

Troubleshooting

References