Manage Windows Installer Cache Size

<#
.SYNOPSIS

    Gets the maximum percentage of disk space the Windows installer can use for
    the cache of old files.

.DESCRIPTION

    If this per-machine system policy is set to a value greater than 0, Windows
    Installer saves older versions of files in a cache when a patch is applied
    to an application.

.LINK

    http://msdn.microsoft.com/en-us/library/windows/desktop/aa369798.aspx

.LINK

    article: http://www.technologytoolbox.com/blog/jjameson/archive/2010/04/30/save-significant-disk-space-by-setting-maxpatchcachesize-to-0.aspx
    github: https://github.com/jeremy-jameson/Toolbox/blob/master/PowerShell/Get-MaxPatchCacheSize.ps1

.EXAMPLE

    .\Get-MaxPatchCacheSize.ps1
    0

    Description
    -----------

    In this example, the MaxPatchCacheSize policy has previously been set to 0 (to
    indicate that no additional files should be saved).
#>

Set-StrictMode -Version Latest
$ErrorActionPreference = "Stop"

[string] $installerPath = "HKLM:\Software\Policies\Microsoft\Windows\Installer"

Get-ItemProperty -Path $installerPath -Name MaxPatchCacheSize |
    ForEach-Object { $_.MaxPatchCacheSize }

<#
.SYNOPSIS

    Sets the maximum percentage of disk space the Windows installer can use for
    the cache of old files.

.DESCRIPTION

    If this per-machine system policy is set to a value greater than 0, Windows
    Installer saves older versions of files in a cache when a patch is applied
    to an application.

.PARAMETER MaxPercentageOfDiskSpace

    The maximum percentage of disk space the installer can use for the cache of
    old files.

.LINK

    http://msdn.microsoft.com/en-us/library/windows/desktop/aa369798.aspx

.LINK

    article: http://www.technologytoolbox.com/blog/jjameson/archive/2010/04/30/save-significant-disk-space-by-setting-maxpatchcachesize-to-0.aspx
    github: https://github.com/jeremy-jameson/Toolbox/blob/master/PowerShell/Set-MaxPatchCacheSize.ps1

.EXAMPLE

    .\Set-MaxPatchCacheSize.ps1
    0

    Description
    -----------
    Sets the value of the MaxPatchCacheSize policy to 0 to indicate that no
    additional files should be saved.

.NOTES

    This script must be run with administrator privileges.
#>
param(
    [parameter(Mandatory=$true)]
    [int] $MaxPercentageOfDiskSpace
)

Set-StrictMode -Version Latest
$ErrorActionPreference = "Stop"

[int] $maxPatchCacheSize = $MaxPercentageOfDiskSpace
[string] $installerPath = "HKLM:\Software\Policies\Microsoft\Windows\Installer"

$installerKey = Get-Item -Path $installerPath -EA 0
if ($installerKey -eq $null)
{
    $installerKey = New-Item -Path $installerPath
}

$currentMaxPatchCacheSize = $installerKey.GetValue("MaxPatchCacheSize")
if ($currentMaxPatchCacheSize -eq $null)
{
    New-ItemProperty -Path $installerPath -Name MaxPatchCacheSize `
        -PropertyType DWord -Value $maxPatchCacheSize | Out-Null
}
elseif ($currentMaxPatchCacheSize -eq $maxPatchCacheSize)
{
    Write-Verbose ("MaxPatchCacheSize is already set to {0}." -f $maxPatchCacheSize)
    exit
}
else
{
    Set-ItemProperty -Path $installerPath -Name MaxPatchCacheSize `
        -Value $maxPatchCacheSize | Out-Null
}

Write-Host -Fore Green ("Successfully set MaxPatchCacheSize to {0}." `
    -f $maxPatchCacheSize)