Courses/PowerShell/Functions and Scripts

Functions and Scripts

Write reusable functions with validated parameters, save scripts as .ps1 files, and handle errors.

Our editor simulates PowerShell output using JavaScript. For real practice, open PowerShell on your system.

What You'll Learn

Writing functions with param blocks and CmdletBinding
Parameter validation (Mandatory, ValidateSet, ValidateRange)
Script files, comment-based help, and #requires
Error handling with try/catch/finally and ErrorAction

Writing Functions

Functions in PowerShell follow the same Verb-Noun convention as cmdlets. A basic function uses a param block for parameters:

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

Get-Greeting -Name "Alice"   # Hello, Alice!

For production-quality functions, add [CmdletBinding()] to enable common parameters like -Verbose, -ErrorAction, and -WhatIf:

function Remove-OldLogs {
    [CmdletBinding(SupportsShouldProcess)]
    param(
        [Parameter(Mandatory)]
        [string]$Path,
        [int]$DaysOld = 30
    )
    $cutoff = (Get-Date).AddDays(-$DaysOld)
    Get-ChildItem $Path -Filter "*.log" |
        Where-Object LastWriteTime -lt $cutoff |
        ForEach-Object {
            if ($PSCmdlet.ShouldProcess($_.Name, "Delete")) {
                Remove-Item $_.FullName
            }
        }
}

⚠️ Common Mistake

Don't use return for every output. In PowerShell, any unassigned expression is output. return is only needed to exit early. Writing return $result works but is unnecessary at the end of a function.

Functions & Parameters

Build functions with validated parameters.

Try it Yourself »

JavaScript

// PowerShell Functions — simulated in JavaScript
console.log("=== Basic Functions ===");
console.log();
console.log("function Get-Greeting {");
console.log('    param([string]$Name = "World")');
console.log('    return "Hello, $Name!"');
console.log("}");
console.log();

// Simulate
function getGreeting(name = "World") { return "Hello, " + name + "!"; }
console.log("PS> Get-Greeting");
console.log("→ " + getGreeting());
console.log("PS> Get-Greeting -Name 'Alice'");
console.log("→ " + getGreeti
...

Scripts, Errors & Modules

Save your functions in .ps1 files and run them with .\script.ps1. Add comment-based help so users can run Get-Help .\script.ps1:

<#
.SYNOPSIS
    Backs up a folder to a timestamp directory.
.PARAMETER Source
    The folder to back up.
.EXAMPLE
    .\Backup-Folder.ps1 -Source C:\Data
#>

PowerShell distinguishes between terminating and non-terminating errors. Use -ErrorAction Stop to make non-terminating errors catchable:

try {
    Get-Content "missing.txt" -ErrorAction Stop
} catch {
    Write-Warning "Error: $($_.Exception.Message)"
}

Scripts & Error Handling

Script structure, error handling, and modules.

Try it Yourself »

JavaScript

// PowerShell Scripts & Error Handling — simulated in JavaScript
console.log("=== Script Files (.ps1) ===");
console.log();
console.log("Save functions in .ps1 files and run them:");
console.log("  PS> .\\my-script.ps1");
console.log("  PS> & 'C:\\Scripts\\backup.ps1'");
console.log();

console.log("=== Script Structure Best Practice ===");
console.log("#requires -Version 7.0");
console.log("#requires -Modules ActiveDirectory");
console.log();
console.log("<#");
console.log(".SYNOPSIS");
console
...

💡 Pro Tip

Create a PowerShell module by saving your functions in a .psm1 file and creating a module manifest (.psd1) with New-ModuleManifest. This lets you version, share, and publish your tools to the PowerShell Gallery.

📋 Quick Reference

Concept	Syntax
Basic function	function Verb-Noun { param(...) }
Mandatory param	[Parameter(Mandatory)]
Validate values	[ValidateSet('A','B')]
Try/catch	try { ... } catch { ... }
Run script	.\script.ps1

🎉 Lesson Complete!

You can now write professional PowerShell functions and scripts. Next up: navigating the file system and Windows registry.