<#

.Synopsis

   Gathers hotfixes for all computers in a list then returns a list of hotfixes that are only installed on some of the nodes.

.DESCRIPTION

   Given a list of computers, this cmdlet verifies each computer is reachable and then gathers a list of hotfixes installed on each computer. It will then either display a table of all hotfixes

   that are only installed on a subset of the computers specified or, if the DisplayAllHotfixes switch is specified, a table of all hotfixes installed on all computers. The first column

   is the HotfixID and each other column (property) is the computer name; if the hotfix is installed on that computer it's marked "True", if not it's marked "False".

.EXAMPLE

   $computerlist = @("ServerA", "ServerB", "ServerC")

   Get-HotfixDiscrepancyReport -ComputerList $serverlist

   Generates a hotfix report for three servers.

.EXAMPLE

   Get-HotfixDiscrepancyReport -Computerlist ComputerA, ComputerB, ComputerC -DisplayAllHotfixes | Export-CSV .\hfreport.csv

   Lists all hotfixes and whether or not they're installed for three computers and exports the list to a CSV file.

#>

function Get-HotfixDiscrepancyReport

{

    [CmdletBinding()]

    [OutputType([PSObject[]])]

    Param

    (

        # A list of computers - can be an array variable or a comma delimited list of computers

        [Parameter(Mandatory=$true,

                   ValueFromPipeline=$true,

                   Position=0)]

        [Array]$ComputerList,

        # If you want to display all hotfixes instead of just hotfixes that aren't installed on every computer

        [Switch]$DisplayAllHotfixes

    )

    Process

    {

        $VerifiedComputers = @()

        foreach ($computer in $ComputerList)

        {

            if(Test-Connection $computer -Count 1 -ErrorAction SilentlyContinue)

            {

                $VerifiedComputers += $computer

            }

            else

            {

            }

        }

        If ($VerifiedComputers.Count -lt 2)

        {

            Write-Error -Message "Not enough computers to generate a report. If your initial list had more than one computer, enable verbose mode to see which computers are failing."

            return

        }

        [hashtable]$InstalledHotfixes = @{}

        Get-WmiObject Win32_QuickFixEngineering -Computername $VerifiedComputers[0] | % {

            $InstalledHotfixes.Add($_.HotfixId, @($VerifiedComputers[0]))

        }

        for ($i = 1; $i -lt $VerifiedComputers.Count; $i++)

        {

            Get-WmiObject Win32_QuickFixEngineering -ComputerName $VerifiedComputers[$i] | % {

                if ($InstalledHotfixes.ContainsKey($_.HotfixID))

                {

                    $InstalledHotfixes.Set_Item($_.HotfixID,($InstalledHotfixes.Get_Item($_.HotfixId) + $VerifiedComputers[$i]))

                }

                else

                {

                    $InstalledHotfixes.Add($_.HotfixId, @($VerifiedComputers[$i]))

                }

            }

        }

        if (!$DisplayAllHotfixes)

        {

            $NewHfList = @{}

            $InstalledHotfixes.GetEnumerator() | % {if ($_.Value.Count -lt $VerifiedComputers.count) {$NewHfList.Add($_.Key,$_.Value)}}

        }

        else

        {

            $NewHfList = $InstalledHotfixes

        }

        $hfdiscrepancylist = @()

        $NewHfList.GetEnumerator() | % {

            $hfditem = "" | Select HotfixID

            $hfditem.HotfixID = $_.Key

            foreach ($computer in $VerifiedComputers)

            {

                $hfditem | Add-Member -NotePropertyName $computer -NotePropertyValue ([boolean]($_.Value -contains $computer))

            }

            $hfdiscrepancylist += $hfditem

        }

        return $hfdiscrepancylist | Sort-Object HotfixID

    }

}