Improved Slipstream script

<#
.SYNOPSIS
   Builds a SQL Server slipstream install.
.DESCRIPTION
   This script will take the various components of a SQL Server isntall (RTM binaries, SPs, CUs) and assemble
     them to create a slipstream install.  To use this script, you will need the unextracted RTM binaries (.iso
     or DVD media) and the executables for the SP and CUs you want to use.
     Mike Fal (htp://www.mikefal.net) 2-28-2013
.PARAMETER <paramName>
   RTMSource - File path for the RTM source files
     SPSource - File path for the Service Pack executables (if no value is passed, no SP will be added)
     CUSource - File path for the Cumulative update executables (if no value is passed, no CU will be added)
     OutputDir - filepath where slipstream will be written, directory will be created if it doesn't exist.
.EXAMPLE
   .\Build-Slipstream.ps1 -RTMSource "C:\Users\mfal\Downloads\en_sql_server_2008_r2_developer_x86_x64_ia64_dvd_522665"
                                                    -SPSource "C:\Users\mfal\Downloads\2008R2SP1"
                                                    -CUSource "C:\Users\mfal\Downloads\2008R2SP1CU2"
                                                    -output "C:\SQL2008SP1CU2_Slipstream"
#>
param(
    [parameter(Mandatory=$true)][string] $RTMSource,
    [parameter(Mandatory=$false)][string] $SPSource = $null,
    [parameter(Mandatory=$false)][string] $CUSource = $null,
    [parameter(Mandatory=$true)][string] $OutputDir
)

#function to extract and copy SPs and CUs
function Modify-Source{
    param($TYPE="PCU",$WORKDIR,$PATCHDIR)
    if (!(test-path("$WORKDIR\$TYPE"))) {mkdir $WORKDIR\$TYPE }
    if (!(test-path("$WORKDIR\$TYPE"))) {Throw "Error: Patch file destination not available"}
    set-location $PATCHDIR

    # First the comprressed service packs
    $PATCHFILES=get-childitem "$PATCHDIR\*" -include *_zip.exe
    foreach($FILE in $PATCHFILES) { iex "7za x -y $FILE"; }

    $PATCHFILES=get-childitem "$PATCHDIR\*" -include *.exe -Exclude *_zip.exe
    foreach($FILE in $PATCHFILES)
    {
        iex "./$($FILE.basename)$($FILE.extension) /x:""$WORKDIR\$TYPE"" /q"
        Write-Host "Waiting for $FILE to extract..."
        while (@(Get-Process $FILE.Name.Replace(".exe","") -ErrorAction SilentlyContinue).Count -ne 0)
        {
            Start-Sleep 1
        }
    }
    Write-Host "Copying $TYPE files..."
    robocopy "$WORKDIR\$TYPE" "$WORKDIR" setup.exe /ndl /nfl /njh /njs
    robocopy "$WORKDIR\$TYPE" "$WORKDIR" setup.rll /ndl /nfl /njh /njs

if (test-path("$WORKDIR\$TYPE\x86")) {robocopy "$WORKDIR\$TYPE\x86" "$WORKDIR\x86" /XF Microsoft.SQL.Chainer.PackageData.dll /ndl /nfl}
if (test-path("$WORKDIR\$TYPE\x64")) {robocopy "$WORKDIR\$TYPE\x64" "$WORKDIR\x64" /XF Microsoft.SQL.Chainer.PackageData.dll /ndl /nfl}
if (test-path("$WORKDIR\$TYPE\ia64")) {robocopy "$WORKDIR\$TYPE\ia64" "$WORKDIR\ia64" /XF Microsoft.SQL.Chainer.PackageData.dll /ndl /nfl}

set-location $WORKDIR
}

#Test path locations for validity

if (!(test-path($RTMSource + "\setup.exe"))) {Throw "SQL RTM Source does not exist!"}
if (![String]::IsNullOrEmpty($SPSource) -and !(test-path($SPSource))) {Throw "Invalid Service Pack file location!"}
if (![String]::IsNullOrEmpty($CUSource) -and !(test-path($CUSource))) {Throw "Invalid Cumulative Update file location!"}
if (!(test-path($OutputDir))) {mkdir $OutputDir}
if (!(test-path($OutputDir))) {Throw "Unable to create build directory!"}

#begin merge process, RTM
Write-Host "Copying RTM..."
robocopy "$RTMSource" "$OutputDir" /s /ndl /nfl /a-:r
$startloc=pwd
set-location $OutputDir

Copy-Item ".\x86\DefaultSetup.ini" ".\"

#merge Service Pack
if(![String]::IsNullOrEmpty($SPSource))
{
    Modify-Source "PCU" $OutputDir $SPSource
    "`n`nPCUSOURCE=`".\PCU`" `n" |Out-File "DefaultSetup.ini" -Append
}

#merge Cumulative Update
if(![String]::IsNullOrEmpty($CUSource))
{
    Modify-Source "CU" $OutputDir $CUSource
    "`n`nCUSOURCE=`".\CU`" `n" |Out-File "DefaultSetup.ini" -Append
}

#cleanup
copy-item "defaultsetup.ini" .\ia64 -force
copy-item "defaultsetup.ini" .\x64 -force
copy-item "defaultsetup.ini" .\x86 -force

Set-Location $startloc