Powershell script to expand archive files using 7zip command line tools

Expand-Item7Zip.ps1

function Expand-Item7zip
{
  param
  (
    [Parameter(Mandatory=$true)] [string] $item,
    [Parameter(Mandatory=$true)] [string] $destinationDirectory
  )

  if (!(Test-Path -Path $item -PathType Leaf))
  {
    throw ("Specified archive File is invalid: " + $item)
  }

  if (!(Test-Path -Path $destinationDirectory -PathType Container))
  {
    New-Item $destinationDirectory -ItemType Directory | Out-Null
  }

    if(!(Get-Command "7z" -ErrorAction SilentlyContinue))
    {
        $7zipInstallationDirectory = "C:\Program Files\7-Zip"
        if(!(Confirm-64BitOS))
        {
            $7zipInstallationDirectory = "C:\Program Files (x86)\7-Zip"
        }

        Set-EnvironmentVariable -name "Path" -value $7zipInstallationDirectory -scope "session" -appendValue
    }

    #& "7z" l $item
    $result = (& "7z" x "-o$destinationDirectory" "$item")
}

function Confirm-64BitOS
{
    (Get-WmiObject -Class Win32_OperatingSystem).OSArchitecture -eq "64-bit"
}
function Set-EnvironmentVariable
{
  param
  (
    [Parameter(Mandatory=$true)] [string] $name,
    [Parameter(Mandatory=$true)] [string] $value,
    [Parameter(Mandatory=$false)] [string] $scope = "process",
    [switch] $appendValue
  )
  $scope = $scope.ToLower()

  if(($scope -ne "machine") -and ($scope -ne "user") -and ($scope -ne "process"))
  {
    THROW New-Object System.Exception "Scope must be 'machine', 'user', or 'process'"
  }

  if($appendValue)
  {
    $newValue = (Get-Item "Env:\$name").Value
    if(!$newValue.Contains($value))
    {
      $newValue += ";$value"
    }
    $value = $newValue
  }
  Set-Item -Path "Env:$name" -Value "$value"
  [Environment]::SetEnvironmentVariable("$name", "$value", "$scope")
}