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Hash Tables - DC operating systems

I have been meaning to get my head around a lot of different aspects of powershell, one of which is hash tables.  As we are currently going through a DC upgrade, I wanted to know how many DC's we had of each different operating system.  I wondered if hash tables would help me.

First, I got all DC's in my domain : 

$DClist = get-ADDomainController -server -filter {enabled -eq $true}
You may notice the get-ad portion of the command....this means that this command runs only on powershell 2 when connected to an Windows 2008 R2 DC or a 2003 / 2008 DC with ADMGS installed. 

So, $DCList is now all the DC's from (-server that are set to enabled (-filter {enabled -eq $true}). 

NOTE: The only DC's that are not enabled are pre-staged RODC accounts ... by that i mean accounts that have been created but the server has not come online yet.  These servers do not have any OS information in them anyway. It is more helpful to filter these when you want to query the online servers later as is only wastes processing power trying to query a server that doesn't really exist yet!.  You can also do -filter {isreadonly -eq $false} to just get read write DC's.

So how do we use hash tables to count all the different os types? First we need to declare a variable as an empty array.

$OSlist = @{}

Next, we pass the operatingsystem attribute via foreach to $oslist AS A NEW ATTRIBUTE. At the same time we want to increment that attribute by 1. The way powershell works is that if the attribute doesn't exist, it will create it prior to adding 1 to it. If it is there, it will increment the existing value.

$DClist | foreach {$OSlist.$($_.operatingsystem) ++}
$DClist | - pass $dclist through the pipeline

foreach { - the foreach statement

$oslist. - accessing an attribute in the variable $oslist

$($_.operatingsystem) - the evaluation of the value of $_.operatingsystem

++} - increment the value $oslist.$($_.operatingsystem) and close the foreach.

for example, if the $($_.operatingsystem) value is the first instance of "Windows 2008 R2", this process will create an attribute in $oslist called "Windows 2008 R2" and then increment it by 1. As it doesn't have a value or a type, powershell assumes it is a number and and the value becomes 1.

At the end of the process, you have attributes corresponding to all the OS's in your environment (no more, no less) and a count of each in 3 lines of code.  Sweet.

$DClist = get-ADDomainController -server -filter {enabled -eq $true}
$OSlist = @{}
$DClist | foreach {$OSlist.$($_.operatingsystem) ++}


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