Defining a Function

function Get-Factorial {
    param([int]$n)
    if ($n -le 1) { return 1 }
    return $n * (Get-Factorial -n ($n - 1))
}

Get-Factorial -n 5   # 120

Key parts:
- function Name { } — declaration (Verb-Noun naming convention, e.g. Get-, Set-)
- param(...) — parameter block with optional type hints like [int], [string]
- return — optional; PowerShell outputs anything not captured, but return makes intent explicit

Recursive Pattern (File Collector)

function Get-AllFiles {
    param([string]$Root)
    $files = @()
    foreach ($entry in Get-ChildItem -Path $Root) {
        if ($entry.PSIsContainer) {
            $files += Get-AllFiles -Root $entry.FullName   # recursive case
        } else {
            $files += $entry.FullName                      # base case
        }
    }
    return $files
}

Base case / recursive case logic is identical to Python's — only syntax differs:
- $entry.PSIsContainer detects directories (true for folders)
- Get-ChildItem lists entries (like os.listdir)
- Parameters are passed as named args: -Root $path

Practical Tips

• $files += ... is convenient but slow on huge trees; prefer building output through the pipeline (Get-ChildItem -Recurse also exists for the simple case).
• Recursion depth in PowerShell is limited — for very deep folder trees, an iterative loop with an explicit stack may be safer.

Compare with Python Function Basics and Recursion — same concepts, different syntax.