Prof. Powershell

Scriptblock Surprises

PowerShell Functions can save you time. Scriptblocks save you even more time.

• By Jeffery Hicks
• 09/14/2010

In Windows PowerShell, if you want to modularize a block of code so that you don't have to keep typing it, one way is to create a function. You can even create them on the fly.

PS C:\> function t {(get-date).ToShortTimeString()}
PS C:\> t
12:30:35 PM

But another way is to use a scriptblock. You actually see scriptblocks all over PowerShell. A scriptblock is a collection of PowerShell code inside a set of curly braces { }.

PS C:\> $sb={get-wmiobject win32_logicaldisk -filter "drivetype=3"}
PS C:\> $sb
get-wmiobject win32_logicaldisk -filter "drivetype=3"

When looking at the scriptblock variable, $sb, we get the definition which I can verify is a scriptblock object.

PS C:\> $sb.gettype().name
ScriptBlock

To execute the scriptblock I merely prepend the invoke operator, &, like this:

PS C:\> &$sb

The pipelined output is the same as if you had run the Get-WMIObject command manually. The scriptblock is in essence a shortcut so I only have to type the command once. There's no limit to the amount of code you can put in a scriptblock. You can separate out multiple commands with a ; if you want to type it all on one line.

PS C:\> $stopped={$stopped=get-service | where {$_.status -eq "stopped"};$stopped | select Name; Write-Host "`nFound $($stopped.count) stopped services" -foregroundcolor green}

Or spread it out like this.

PS C:\> $stopped={$stopped=get-service | where {$_.status -eq "stopped"}
>> $stopped | select Name
>> Write-Host "`nFound $($stopped.count) stopped services" -foregroundcolor green}
>>
PS C:\>

They'll both work the same way when you invoke $stopped. The last part of the scriptblock lesson is how to pass parameters. Let's go back to my first WMI scriptblock. Wouldn't it be nice to be able to specify a computername? You can by defining a parameter as part of your scriptblock.

PS C:\> $sb={Param([string]$computername=$env:computername) get-wmiobject win32_logicaldisk -filter "drivetype=3" -computername $computername}

The Param statement contains a comma separated list of parameters. My example only has one. Use the variable within your scriptblock. I strongly recommend providing a default value. In this example, the default computer is the local host. That means no errors when I invoke the scriptblock:

PS C:\> &$sb

Or I can specify a computername:

PS C:\> &$sb jdhit-dc01

Because I only have one parameter I don't have to specify it, but I could if I wanted to.

PS C:\> &$sb -computername jdhit-dc01

Otherwise keep in mind that parameters are positional.

If you need a lot of error handling or a more robust solution then developing a function is the better way to go. But for quick and re-usable code to save typing and your sanity, I encourage you to explore scriptblocks. You might be pleasantly surprised.

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