PowerShell for Windows Admins

November 19, 2015  2:49 PM

Splatting and Default parameters

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

One thing you don’t hear much about is default parameters.

Consider this

Get-CimInstance -ClassName Win32_LogicalDisk -Filter “DeviceId = ‘C:'”

A pretty standard use of CIM.

Now think if you have to do this across a number of machines on a regular basis. Typing could get a bit tedious.

You could use splatting:

$params = @{
ClassName = ‘Win32_LogicalDisk’
Filter = “DeviceId = ‘C:'”

Get-CimInstance @params

Create a hash table of parameter names and values and use that to reduce your typing. Because its a hash table you can modify as required to use other classes or Filters

An alternative is to use default parameters

$PSDefaultParameterValues = @{
‘Get-CimInstance:ClassName’ = ‘Win32_LogicalDisk’
‘Get-CimInstance:Filter’ = “DeviceId = ‘C:'”


Use the $PSDefaultParameterValues variable to hold your default values. Note how the cmdlet and parameter are defined. You can then call the cmdlet and the default parameters and their values are applied.

If you want to override the default values you may have to do it for all of the default values for a cmdlet – in the above case the Filter is nonsensical if applied to Win32_OperatingSystem so you’d have to do this

Get-CimInstance -ClassName Win32_OperatingSystem -Filter “Manufacturer LIKE ‘%'”

Used with a bit of care splatting and default parameters are a good way to save typing

November 18, 2015  8:10 AM

Out of Process

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

One thing I’ve been seeing come up a lot recently is the problem of modules and cmdlets cot being available when jobs and workflows are executed even though the module has been specifically loaded into PowerShell.

This is because workflows and Jobs run in a separate process when you execute them – NOT your current PowerShell process. The worflow or job process doesn’t run your profile and doesn’t auto load modules.

You need to specifically perform the module import. Remember you can’t use Import-Module in a workflow so you have to wrap that part in an InlineScript block.

November 16, 2015  12:51 PM

Accessing WMI

Richard Siddaway Richard Siddaway Profile: Richard Siddaway
Powershell, WMI

There are 3 sets of cmdlets for working with WMI classes – the WMI cmdlets, the WSMAN cmdlets and the CIM cmdlets. The protocols used by these 3 sets are different.

The WMI cmdlets introduced in PowerShell 1 & 2 use DCOM for local and remote access under all circumstances

The WSMAN cmdlets introduced in PowerShell 2 use WSMAN (WinRm)

The CIM cmdlets introduced in PowerShell 3 use:

– DCOM for local access if ComputerName parameter NOT used

– WSMAN for local access IF –ComputerName parameter is used

– WSMAN (WinRM) for remote access

– WSMAN if a default CIM session is used for remote access

– DCOM if a CIM session is created using DCOM as the protocol option

The CIM cmdlets are easier to use than the WSMAN cmdlets and are the recommended way to access WMI classes.

November 14, 2015  12:51 PM

PowerShell + DevOps Global Summit 2016 – the agenda

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

We’ve finalised the agenda and we’re starting to publish session information on the web site at


There are a handful of sessions on the site at present. The rest will be added over the next week or so.

Keep checking back to see who’s been added.

Registration opens 1 December 2015

November 11, 2015  2:00 PM

WMI wildcards and filtering

Richard Siddaway Richard Siddaway Profile: Richard Siddaway
CIM, Powershell, WMI

A question on the forum asking about filtering WMI results raises a number of interesting points.

The user wanted to pass a computername and a filter term to pull product information from remote machines. I ended up with this

$computername = $env:COMPUTERNAME
$filter = ‘Live’

$scriptblock = {
Get-WmiObject -Class Win32_product -Filter “Name LIKE ‘%$filter%'” |
Select  IdentifyingNumber, Name, LocalPackage }

Invoke-Command -ComputerName $computername -ScriptBlock $scriptblock -ArgumentList $filter

You can pass an argument into the scriptblock you use with invoke-command by using the –Argumentlist parameter.

More interesting is the –Filter parameter on Get-Wmi-Object

-Filter “Name LIKE ‘%$filter%'”

Notice that % is the wildcard not * as you’d use for a string.  Its always better to filter the results from Get-WmiObject using –Filter rather than a where-object after the call.

Of course you can just use the wmi or cim cmdlets directly for this problem which is even better

Get-WmiObject -Class Win32_Product -ComputerName $computername -Filter “Name LIKE ‘%$filter%'” | Select  IdentifyingNumber, Name, LocalPackage

Get-CimInstance -ClassName Win32_Product -ComputerName $computername -Filter “Name LIKE ‘%$filter%'” | Select  IdentifyingNumber, Name, LocalPackage

November 6, 2015  1:48 PM

PowerShell in Action, 3e MEAP 2

Richard Siddaway Richard Siddaway Profile: Richard Siddaway
Books, Powershell

Another chapter of PowerShell in Action third edition has been released into the MEAP process. – see https://manning.com/books/windows-powershell-in-action-third-edition

November 4, 2015  5:13 AM

WMI cmdlets and credentials

Richard Siddaway Richard Siddaway Profile: Richard Siddaway
Powershell, WMI

If you’re working with the WMI cmdlets and need to pass credentials you’ll end up with a statement something like this

Get-WmiObject -Class Win32_ComputerSystem -ComputerName $computer -Credential $cred

If the computer name defaults to the local host or you use . or ‘localhost’ as the computer name you’ll get an error

PS> Get-WmiObject -Class Win32_ComputerSystem -ComputerName $env:COMPUTERNAME  -Credential $cred
Get-WmiObject : User credentials cannot be used for local connections
At line:1 char:1
+ Get-WmiObject -Class Win32_ComputerSystem -ComputerName $env:COMPUTER …
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo          : InvalidOperation: (:) [Get-WmiObject], ManagementException
+ FullyQualifiedErrorId : GetWMIManagementException,Microsoft.PowerShell.Commands.GetWmiObjectCommand

You need to build in some logic to prevent credentials being used ig you’re working against the local machine.  One way to this is to create a bunch of Get-WmiObject statements and use if statements to decide which to use.

I think there’s a neater way if you use splatting

#$computer = $env:COMPUTERNAME
#$computer = ‘localhost’
#$computer = ‘.’
$computer = ‘server02’

$params = @{
‘Class’ =  ‘Win32_ComputerSystem ‘
‘ComputerName’ = $computer

switch ($computer){
“$env:COMPUTERNAME” {break}
‘localhost’ {break}
‘.’   {break}
default {$params += @{‘Credential’ = $cred}}

Get-WmiObject @params

Splatting involves creating a hash table of the parameters and their values. You can then use a switch statement to decide if computer matches any of the local name variants. If it doesn’t then add the credential

You could extend this slightly to cope with not having a computer name  in the initial set of params and only add it if required

$params = @{
‘Class’ =  ‘Win32_ComputerSystem’

if ($computer) {
$params += @{‘ComputerName’ = $computer}

switch ($computer){
“$env:COMPUTERNAME” {break}
‘localhost’ {break}
‘.’   {break}
default {$params += @{‘Credential’ = $cred}}

Get-WmiObject @params

Then you only test the computer name if you need to.

October 30, 2015  11:37 AM

Creating DNS records

Richard Siddaway Richard Siddaway Profile: Richard Siddaway
DNS, Powershell

Following on from my previous post about creating a reverse lookup zone in DNS here’s a function to create records in that zone.

The function takes an IP address and name (of host) and uses Add-DnsServerResourceRecordA  to add the record to the forward lookup zone – I use my default AD zone.

The function then splits the IP address. Uses the last octet for the name in the reverse record. Creates the reverse lookup zone from the first 3 octets – notice how the range parameter is used in a decreasing way to specify the order of the octets – to create the reverse lookup zone. The host name and zone are used to create the FQDN of the host.

Add-DnsServerResourceRecordPtr  is used to create the reverse (PTR) record.

function new-dnsrecord {
param (
[string]$zone = ‘Manticore.org’

Add-DnsServerResourceRecordA -Name $name -ZoneName $zone -AllowUpdateAny -IPv4Address $ipaddress

$octs = $ipaddress -split ‘\.’

$revname = “$($octs[3])”
$revzone = “$($octs[2..0] -join ‘.’).in-addr.arpa”
$fqdn = “$name.$zone”

Add-DnsServerResourceRecordPtr -Name $revname -ZoneName $revzone -AllowUpdateAny -PtrDomainName $fqdn


October 30, 2015  11:36 AM

Create a reverse lookup zone

Richard Siddaway Richard Siddaway Profile: Richard Siddaway
DNS, Powershell

I needed to create a DNS reverse lookup zone for my test environment. With Windows Server 2012 R2 I’ve got cmdlets available for managing DNS servers – the DnsServer module. You need to install the DNS role or the DNS RSAT tools to get access to the module.

To create a new reverse lookup zone

Add-DnsServerPrimaryZone -DynamicUpdate Secure -NetworkId ‘’ -ReplicationScope Domain

Use the networkId to define the subnet the zone spans. Setting DynamicUpdate to Secure ensures I have an AD integrated zone and I’ve set the replication scope to the domain.

Doesn’t get any easier

October 29, 2015  12:31 PM

Win free entry to the PowerShell Summit

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

Want to go to the PowerShell Summit? Want to go for free?

You can win free entry to the Summit (need to pay your own travel & hotel) through the competition at http://powershell.org/wp/2015/10/28/win-a-free-4-day-pass-to-powershell-and-devops-summit-2016/

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