Functions

A function is a named, reusable block of code. In PowerShell, a function behaves just like a cmdlet: you call it by name, pass parameters, and pipe its output.

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

Get-Greeting
Get-Greeting -Name Ada
Get-Greeting Linus

Hello, world!
Hello, Ada!
Hello, Linus!

• Name functions Verb-Noun with an approved verb, like cmdlets.
• Parameters go in a param() block, exactly like script parameters.
• Call a function with spaces between arguments — never with parentheses and commas.

Everything uncaptured is output

A function's output is every value it doesn't capture or discard — not just what follows return:

function Get-Numbers {
  'starting'
  $list = [System.Collections.Generic.List[int]]::new()
  $list.Add(1)
  $list.Add(2)
  return $list
}

$result = Get-Numbers
$result.Count
$result[0]

3
starting

The function returned three values: the string 'starting' and the two numbers in the list (PowerShell unrolls collections as they're output). Stray output is the most common function bug — silence unwanted values with $null = ... or | Out-Null, and use Write-Verbose for progress messages.

return exits the function; return $x outputs $x and then exits.

Common mistakes

function Add-Numbers {
  param([int]$A, [int]$B)
  $A + $B
}

Add-Numbers 2 3
Add-Numbers(2, 3)

5
Add-Numbers: C:\demo\script.ps1:7
Line |
   7 |  Add-Numbers(2, 3)
     |             ~~~~~~
     | Cannot process argument transformation on parameter 'A'. Cannot convert the "System.Object[]" value of type
     | "System.Object[]" to type "System.Int32".

Add-Numbers(2, 3) passes one argument — the array 2, 3 — to $A. It can't convert an array to [int], so it fails. Use Add-Numbers 2 3 or, better, Add-Numbers -A 2 -B 3.

Practice

Write Get-Area that takes -Width and -Height and returns their product.

function Get-Area {
  param([double]$Width, [double]$Height)
  $Width * $Height
}
Get-Area -Width 4 -Height 2.5

10