UnZipJustSubDir

Expand-ZipSubdirectory.ps1

function Expand-ZipSubdirectory {
<#
.SYNOPSIS
Extracts only a specific subdirectory from a ZIP archive.

.DESCRIPTION
Expand-ZipSubdirectory allows selective extraction of a single subdirectory
from a ZIP file. Unlike Expand-Archive, which extracts the entire archive,
this function filters ZIP entries by path and extracts only the matching
subtree.

The function validates:
- The ZIP file exists and has a .zip extension
- The destination directory exists or can be created
- The subdirectory parameter is not empty

ZIP archives always use forward slashes internally. The function normalizes
the provided subdirectory path automatically.

.PARAMETER ZipPath
The full path to the .zip file. Must exist and must have a .zip extension.

.PARAMETER Subdirectory
The internal ZIP subdirectory to extract. This should be the folder path
inside the ZIP (e.g., "module/MicrosoftFabricMgmt").

.PARAMETER Destination
The directory where the extracted files will be placed. If it does not exist,
the function attempts to create it.

.PARAMETER Force
If specified, existing files in the destination will be overwritten.

.EXAMPLE
Expand-ZipSubdirectory -ZipPath "C:\temp\package.zip" `
                       -Subdirectory "module/MicrosoftFabricMgmt" `
                       -Destination "C:\temp\extract"

Extracts only the MicrosoftFabricMgmt subdirectory from the ZIP.

.EXAMPLE
Expand-ZipSubdirectory -ZipPath ".\build.zip" `
                       -Subdirectory "output/bin" `
                       -Destination ".\bin" `
                       -Force

Extracts the "output/bin" folder and overwrites existing files.

.NOTES
This function uses System.IO.Compression.ZipFile from .NET and does not rely
on Expand-Archive. It supports nested directories and preserves structure.

#>

    [CmdletBinding()]
    param(
        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [ValidateScript({
            if (-not (Test-Path $_)) {
                throw "ZipPath '$_' does not exist."
            }
            if (-not ($_ -match '\.zip$')) {
                throw "ZipPath '$_' is not a .zip file."
            }
            $true
        })]
        [string]$ZipPath,

        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [string]$Subdirectory,

        [Parameter(Mandatory)]
        [ValidateNotNullOrEmpty()]
        [ValidateScript({
            if (-not (Test-Path $_)) {
                try {
                    New-Item -ItemType Directory -Path $_ -ErrorAction Stop | Out-Null
                }
                catch {
                    throw "Destination '$_' does not exist and could not be created."
                }
            }
            $true
        })]
        [string]$Destination,

        [switch]$Force
    )

    # Normalize ZIP internal path format
    $normalized = $Subdirectory.TrimStart('/','\') -replace '\\','/'
    if (-not $normalized.EndsWith('/')) {
        $normalized += '/'
    }

    Add-Type -AssemblyName System.IO.Compression.FileSystem
    $zip = [System.IO.Compression.ZipFile]::OpenRead($ZipPath)

    try {
        $matched = $false

        foreach ($entry in $zip.Entries) {
            if ($entry.FullName.StartsWith($normalized, [StringComparison]::OrdinalIgnoreCase)) {
                $matched = $true

                $relative = $entry.FullName.Substring($normalized.Length)
                if (-not $relative) { continue }

                $target = Join-Path $Destination $relative
                $targetDir = Split-Path $target

                if (-not (Test-Path $targetDir)) {
                    New-Item -ItemType Directory -Path $targetDir | Out-Null
                }

                if ($entry.Name) {
                    [System.IO.Compression.ZipFileExtensions]::ExtractToFile($entry, $target, $Force.IsPresent)
                }
            }
        }

        if (-not $matched) {
            throw "Subdirectory '$Subdirectory' was not found inside the ZIP."
        }
    }
    finally {
        $zip.Dispose()
    }
}

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