variables in strings with powershell

Question

Im trying to build a variable consisting of several other variables to then include, eg:

$myString = "{$_.Name -like "
$myString += $computer[0]
$myString += " -Or $_.Name -like "
$myString += $computer[1]+"}"

Get-VM | Where $myString

I've tried all possible combinations with $($myString),$myString,${$myString}, etc ... It still lists all computers as if there been no filter to it. If i ECHO the Get-VM... it looks prefectly fine and if i cut'n'paste it it works.

Any one got a clue?

You can't use a string in this way, you need a scriptblock.

CB.
– CB.

2013-03-19 14:59:28 +00:00
Commented Mar 19, 2013 at 14:59 — CB.
– CB., Commented Mar 19, 2013 at 14:59

mjolinor · Accepted Answer · 2013-03-19 15:07:38Z

3

Where-Object filters are scriptblocks. Script blocks are compiled before runtime, and the variable references in them are fixed in the scriptblock then. One way to delay that is to use [scriptblock]::create to create the script block after the local variables are set, just before you use it.

$myString = "$_.Name -like "
$myString += $computer[0]
$myString += " -Or $_.Name -like "
$myString += $computer[1]

$filter = [scriptblock]::create($myString)

Get-VM | Where $filter

answered Mar 19, 2013 at 15:07

mjolinor

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1 Comment

Jocke Over a year ago

My savior! Thanks for both the explanation of ScriptBlocks and the solution! Worked like a charm. :)

Frode F. · Accepted Answer · 2013-03-19 15:13:45Z

1

You should use a scriptblock. It will expand the variables every time you call it. I got Hyper-V installed myself, so I made an example for you:

PS > $computer = "DC", "SQL"

$mywherestatement = { $_.Name -like $Computer[0] -or $_.Name -like $Computer[1] }

Get-VM | Where $mywherestatement

Name State CPUUsage(%) MemoryAssigned(M) Uptime   Status
---- ----- ----------- ----------------- ------   ------
DC   Saved 0           0                 00:00:00 Operating normally
SQL  Saved 0           0                 00:00:00 Operating normally



PS > $computer = "CLIENT", "WebDev"

Get-VM | Where $mywherestatement

Name   State CPUUsage(%) MemoryAssigned(M) Uptime   Status
----   ----- ----------- ----------------- ------   ------            
CLIENT Saved 0           0                 00:00:00 Operating normally
WebDev Saved 0           0                 00:00:00 Operating normally

If your $computer array only contains the names you want to check, I'd use -contains instead, because it will work with arrays of any size. Ex:

PS > $computer = "DC", "SQL", "CLIENT", "WebDev"

Get-VM | Where { $Computer -contains $_.Name }

Name   State CPUUsage(%) MemoryAssigned(M) Uptime   Status            
----   ----- ----------- ----------------- ------   ------            
CLIENT Saved 0           0                 00:00:00 Operating normally
DC     Saved 0           0                 00:00:00 Operating normally
SQL    Saved 0           0                 00:00:00 Operating normally
WebDev Saved 0           0                 00:00:00 Operating normally

edited Mar 19, 2013 at 15:13

answered Mar 19, 2013 at 15:06

Frode F.

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6 Comments

Jocke Over a year ago

Thanks C.B. and Graimer, the problem is that i can be either 1, 5, 14 computers i want to filter so i have to dynamicaly build the $_.Name -like according to the numbers of computers i want to filter thats why im built in a string, what i didnt mention in my original post is that i do a loop building the string based on number of computers.

Frode F. Over a year ago

see the updated answer. If you really need to build the string ($computers has more then the VMs you want to get), you should use mjolinor's answer. Personally I would've made the script work with -contains :)

Jocke Over a year ago

Going nuts, what i have is ForEach($VM in (Get-VM | where $mywherestatement)) { with the -containsit comes up empty, i'll have a go with mjolionr's answer and see if it goes better...

Frode F. Over a year ago

I'm sorry, but if it didn't work, you didn't use it right. The last example in my answer works perfectly, using -contains works perfectly with ForEach($VM in (Get-VM | where { $Computer -contains $_.Name })) {.

Jocke Over a year ago

No need to be sorry @Graimer, you're help was most appreciated. Can it be because i'm using a wildcard in the $Computer-array? This is my result if trying with -contains:

Where-Object : Cannot convert 'dc-cust* ' to the type  System.Management.Automation.ScriptBlock' required by parameter 'FilterScript'. Specified method is not supported.

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