PowerShell for Windows Admins

Dec 18 2015   12:53PM GMT

Inputting computer names

Richard Siddaway Richard Siddaway Profile: Richard Siddaway

Tags:
Powershell

Somehting I was writing yesterday started me thinking about the way you input a list of computer names to a cmdlet. Many cmdlets have a ComputerName parameter so knowing how to deal with this sort of input will help. There are a range of techniques.

One of the simplest approaches is to create your list as a variable and use the variable:

$servers = ‘SERVER02’, ‘W12R2SCDC01’, ‘W12R2SUS’, ‘W12R2DSC’, ‘W12R2TGT’, ‘W12R2WEB01’, ‘W12R2WEB02’, ‘W12R2OD01’
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName $servers

If you don’t need the server list as a variable then input it directly to the cmdlet

Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName ‘SERVER02’, ‘W12R2SCDC01’, ‘W12R2SUS’, ‘W12R2DSC’, ‘W12R2TGT’, ‘W12R2WEB01’, ‘W12R2WEB02’, ‘W12R2OD01’

The drawback is that the list of machine names is embedded in your code. The variable approach above is easier to maintain

A common approach is to use Foreach-Object

$servers = ‘SERVER02’, ‘W12R2SCDC01’, ‘W12R2SUS’, ‘W12R2DSC’, ‘W12R2TGT’, ‘W12R2WEB01’, ‘W12R2WEB02’, ‘W12R2OD01’
$servers | foreach {Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName $psitem}

This works but adds unnecessary code. If you are performing other tasks in the foreach processing it may be worthwhile

Likewise using a foreach loop

$servers = ‘SERVER02’, ‘W12R2SCDC01’, ‘W12R2SUS’, ‘W12R2DSC’, ‘W12R2TGT’, ‘W12R2WEB01’, ‘W12R2WEB02’, ‘W12R2OD01’
foreach ($server in $servers) {
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName $server
}

The foreach loop will be quicker but use more memory.

If you create a CSV file make sure you use ComputerName as the field header – then you can do this

Import-Csv .\computers.csv |
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’

if the header is something else – eg computer – then you need to use foreach-object

Import-Csv .\computers.csv |
foreach {
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName $_.Computer
}

Import-Csv .\computers.csv |
foreach {
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName $psitem.Computer
}

If you have the names in a text file you may be tempted to do this

Get-Content .\computers.txt |
foreach {
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName $_
}

You can also use $psitem instead of $_

A neater way is to do this

Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName (Get-Content .\computers.txt)

which gets us back to the PowerShell one liner solution.

If you’re reading the computernames from Active Directory you have to do a bit of work because the AD cmdlets don’t return a computerName property – they return name.

You can either

Get-ADComputer -Filter * |
foreach {
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3′ -ComputerName $psitem.Name
}

or if you want to be a bit cleverer

Get-ADComputer -Filter * |
select @{N=’ComputerName’; E = {$_.Name}} |
Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’

Use select-object to create a computername property on the pipeline object.

You can of course revert to the one liner solution

Get-CimInstance -ClassName Win32_LogicalDisk -Filter ‘DriveType=3’ -ComputerName (Get-ADComputer -Filter * | select -ExpandProperty name)

Use ExpandProperty on select-object to strip out the Name value and pass that to your cmdlet.

As you can see there are many ways to achieve the same goal – some easier than others. These examples aren’t necessarily complete.

Next time you need to pass a list of values to a cmdlet stop and think about the best way to do it. You might save some typing and more efficient code.

 Comment on this Post

 
There was an error processing your information. Please try again later.
Thanks. We'll let you know when a new response is added.
Send me notifications when other members comment.

Forgot Password

No problem! Submit your e-mail address below. We'll send you an e-mail containing your password.

Your password has been sent to:

Share this item with your network: