Prof. Powershell

Group Hash

Group-Object, we hardly knew ye. One more tip before we close the book on you.

• By Jeffery Hicks
• 07/13/2010

This time, we wrap up the short series on grouping in Windows PowerShell using the Group-Object cmdlet. But there's one more useful approach I want to make sure you learn. We have been working with GroupInfo object that Group-Object creates. However, you can instruct Group-Object to create a hash table instead:

PS C:\> $hash=Get-WmiObject -Class win32_service | Group-Object -Property StartMode -AsHashTable

I now have a hash table, also known as an associative array, of all services organized by their start mode:

PS C:\> $hash

Name     Value
----     -----
Manual   {\\SERENITY\root\cimv2:Win32_Service.Name="AeLookup...
Auto     {\\SERENITY\root\cimv2:Win32_Service.Name="AudioEnd...
Disabled {\\SERENITY\root\cimv2:Win32_Service.Name="cfWiMAXS...

Hash tables make it easier to work with the underlying connections. For example, I can easily count how many services are configured to autostart:

PS C:\> $hash.auto.count
66

Getting all counts isn't that much more difficult:

PS C:\> $hash.GetEnumerator() | Format-Table -Property name,@{name="Count";Expression={$hash.item($_.name).count }} -auto

Name     Count
----     -----
Manual   103
Auto     66
Disabled 12

I use the GetEnumerator() method so that I get an object with properties to work with.

The hash table approach also makes it easier to get information about each group. For example, I wonder what services are configured as disabled?

PS C:\> $hash.disabled | Select Name

Name
----
cfWiMAXService
clr_optimization_v2.0.50727_32
clr_optimization_v2.0.50727_64
CscService
Mcx2Svc
MSSQLServerADHelper100
NetMsmqActivator
NetPipeActivator
NetTcpActivator
NetTcpPortSharing
RemoteAccess
WMPNetworkSvc

Or which services should be running automatically but aren't?

PS C:\> $hash.auto | where {$_.state -ne "running"} | select Name,StartMode,State

Name                           StartMode State
----                           --------- -----
clr_optimization_v4.0.30319_32 Auto      Stopped
clr_optimization_v4.0.30319_64 Auto      Stopped
MMCSS                          Auto      Stopped
sppsvc                         Auto      Stopped
WSearch                        Auto      Stopped

By grouping objects and creating a hash table I have a great deal of flexibility. Remember, I have the full WMI service object to work with. You might want to try some creative hashing of your own. Here are some ideas to get you started:

Get-WmiObject -Class win32_service | Group-Object -Property StartName –AsHashTable
Get-WmiObject -Class win32_service | Group-Object -Property State –AsHashTable
Get-WmiObject -Class win32_service -computername (get-content computers.txt) | Group-Object -Property SystemName -AsHashTable

Have fun and next time, we'll get, like, totally modular!

• Code Download