Practical Guide to PowerShell

Introduction

PowerShell is a task automation framework and command-line shell from Microsoft. It combines the command-line speed, flexibility, and power of shells like Bash with the familiarity and consistency of the Windows environment and .NET framework.

Visit the PowerShell Docs

Key Features

Basic Concepts

Cmdlets

PowerShell commands (cmdlets) follow a verb-noun naming convention:

Pipeline

PowerShell passes objects (not text) between commands:

Get-Process | Sort-Object CPU -Descending | Select-Object -First 5

Aliases

Common command aliases:

# List all aliases
Get-Alias

# Common aliases
ls  -> Get-ChildItem
cd  -> Set-Location
dir -> Get-ChildItem
cls -> Clear-Host

PowerShell Commands (Cmdlets)

Basic Navigation

# Change directory
Set-Location C:\Users
cd C:\Users

# List directory contents
Get-ChildItem
ls

# Get current directory
Get-Location
pwd

# Create new directory
New-Item -ItemType Directory -Path "NewFolder"
mkdir NewFolder

File Operations

# Create new file
New-Item -ItemType File -Path "test.txt"

# Copy file
Copy-Item "source.txt" -Destination "destination.txt"

# Move file
Move-Item "source.txt" -Destination "new_location\source.txt"

# Delete file
Remove-Item "file.txt"

# Read file content
Get-Content "file.txt"

# Write to file
Set-Content -Path "file.txt" -Value "Hello, World!"
Add-Content -Path "file.txt" -Value "Additional line"

Variables and Data Types

Variable Declaration and Assignment

# Basic variable assignment
$name = "John"
$age = 30
$isActive = $true

# Strongly typed variables
[string]$name = "John"
[int]$age = 30
[bool]$isActive = $true

# Arrays
$array = @(1, 2, 3, 4, 5)
$stringArray = @("apple", "banana", "orange")

# HashTables
$hash = @{
    Name = "John"
    Age = 30
    City = "New York"
}

Working with Variables

# Check variable type
$name.GetType()

# Variable scope
$global:globalVar = "Global scope"
$script:scriptVar = "Script scope"
$local:localVar = "Local scope"

# Environment variables
$env:PATH
$env:USERPROFILE

Flow Control

If-Else Statements

$age = 25

if ($age -gt 18) {
    Write-Host "Adult"
} elseif ($age -eq 18) {
    Write-Host "Just turned adult"
} else {
    Write-Host "Minor"
}

Loops

# ForEach loop
foreach ($item in $array) {
    Write-Host $item
}

# ForEach-Object in pipeline
1..5 | ForEach-Object { $_ * 2 }

# For loop
for ($i = 0; $i -lt 5; $i++) {
    Write-Host $i
}

# While loop
$counter = 0
while ($counter -lt 5) {
    Write-Host $counter
    $counter++
}

# Do-While loop
do {
    Write-Host $counter
    $counter++
} while ($counter -lt 5)

Functions and Scripts

Basic Function

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

# Call function
Get-Greeting
Get-Greeting -name "John"

Advanced Function

function Get-SystemInfo {
    [CmdletBinding()]
    param(
        [Parameter(Mandatory=$true)]
        [string]$ComputerName,
        
        [Parameter()]
        [switch]$IncludeMemory
    )
    
    begin {
        Write-Verbose "Starting system info collection"
    }
    
    process {
        $os = Get-WmiObject -Class Win32_OperatingSystem -ComputerName $ComputerName
        $cpu = Get-WmiObject -Class Win32_Processor -ComputerName $ComputerName
        
        $result = [PSCustomObject]@{
            ComputerName = $ComputerName
            OSVersion = $os.Version
            CPUName = $cpu.Name
        }
        
        if ($IncludeMemory) {
            $result | Add-Member -MemberType NoteProperty -Name TotalMemoryGB -Value ($os.TotalVisibleMemorySize/1MB)
        }
        
        return $result
    }
    
    end {
        Write-Verbose "Completed system info collection"
    }
}

Working with Files and Folders

File System Navigation

# List all files in directory
Get-ChildItem -Path C:\Users -Recurse

# Filter files by extension
Get-ChildItem -Path C:\Users -Filter *.txt

# Find files modified in last 24 hours
Get-ChildItem -Path C:\Users -Recurse |
    Where-Object { $_.LastWriteTime -gt (Get-Date).AddDays(-1) }

File Content Operations

# Read file content
$content = Get-Content -Path "file.txt"

# Read specific lines
Get-Content -Path "file.txt" -TotalCount 5
Get-Content -Path "file.txt" | Select-Object -First 5

# Search file content
Get-Content -Path "file.txt" | Select-String -Pattern "search term"

# Compare files
Compare-Object -ReferenceObject (Get-Content "file1.txt") -DifferenceObject (Get-Content "file2.txt")

System Administration Tasks

Service Management

# List all services
Get-Service

# Get specific service
Get-Service -Name "wuauserv"

# Start/Stop service
Start-Service -Name "wuauserv"
Stop-Service -Name "wuauserv"

# Get service status
Get-Service -Name "wuauserv" | Select-Object Status

Process Management

# List all processes
Get-Process

# Find specific process
Get-Process -Name "notepad"

# Stop process
Stop-Process -Name "notepad"

# Start new process
Start-Process "notepad.exe"

Windows Updates

# Check for updates
Get-WindowsUpdate

# Install updates
Install-WindowsUpdate

# Get update history
Get-WUHistory

Error Handling

Try-Catch Blocks

try {
    # Attempt something that might fail
    $result = 1/0
} catch {
    # Handle the error
    Write-Error "An error occurred: $_"
} finally {
    # Always execute this block
    Write-Host "Cleanup operations"
}

Error Preference

# Set error action preference
$ErrorActionPreference = "Stop"  # Stop on all errors
$ErrorActionPreference = "Continue"  # Continue on non-terminating errors
$ErrorActionPreference = "SilentlyContinue"  # Suppress error messages

# Use -ErrorAction parameter
Get-Process -Name "NonExistentProcess" -ErrorAction SilentlyContinue

PowerShell Profiles

Profile Locations

# Show all profile paths
$PROFILE | Select-Object *

# Create profile if it doesn't exist
if (!(Test-Path -Path $PROFILE)) {
    New-Item -ItemType File -Path $PROFILE -Force
}

Common Profile Settings

# Add to profile
function prompt {
    "PS $($executionContext.SessionState.Path.CurrentLocation)> "
}

# Set aliases
Set-Alias -Name np -Value notepad.exe

# Set default location
Set-Location C:\Users\Username\Documents

Best Practices

Code Style

# Use proper verb-noun naming
function Get-UserInfo {
    # Function implementation
}

# Use proper parameter names
function Get-Data {
    param(
        [Parameter(Mandatory=$true)]
        [string]$Path,
        
        [Parameter()]
        [switch]$Force
    )
}

# Use comment-based help
<#
.SYNOPSIS
    Brief description
.DESCRIPTION
    Detailed description
.PARAMETER Path
    Path parameter description
.EXAMPLE
    Example usage
#>

Performance Tips

# Use proper filtering
# Good
Get-ChildItem -Filter *.txt
# Bad
Get-ChildItem | Where-Object { $_.Name -like "*.txt" }

# Use proper pipeline handling
# Good
$processes = Get-Process
$processes | ForEach-Object { $_.Name }
# Bad
Get-Process | ForEach-Object { $_.Name }

Advanced Topics

Remote Management

# Enable remote management
Enable-PSRemoting

# Start remote session
Enter-PSSession -ComputerName "RemoteComputer"

# Run command on remote computer
Invoke-Command -ComputerName "RemoteComputer" -ScriptBlock {
    Get-Process
}

PowerShell Jobs

# Start background job
Start-Job -ScriptBlock {
    Get-Process
}

# Get job status
Get-Job

# Get job results
Receive-Job -Id 1

# Remove job
Remove-Job -Id 1

PowerShell Classes

class Person {
    [string]$Name
    [int]$Age
    
    Person([string]$name, [int]$age) {
        $this.Name = $name
        $this.Age = $age
    }
    
    [string]ToString() {
        return "$($this.Name) is $($this.Age) years old"
    }
}

# Use class
$person = [Person]::new("John", 30)
$person.ToString()