How to dynamically reference a powershell variable

Question

I have an array that contains different rows where one column identifies the "record" "type." I want to iterate through this array and sort each item based on that value into a new array so that I have one array per type.

Here's what I have so far:

$data = Get-ADObject -SearchBase $sb -filter * -properties * | select samaccountname,canonicalname,objectclass,distinguishedname | sort objectclass,samaccountname
$oct = $data | select objectclass -Unique
foreach ($o in $oct)
{
  $oc = $o.objectclass
  Remove-Variable -name "$oc"
  New-Variable -name "$oc" -value @()
}
$d = @()
$user = @()
foreach ($d in $data)
{
  $oc = $d.objectclass
  foreach ($o in $oct)
  {
    $1 = $o.objectclass
    if ($1 -eq $oc)
    {
      ('$' + $oc) += $d
    }
  }
}

(the lines: Remove-Variable -name "$oc", $d = @(), and $user = @() are for testing purposes so ignore those)

This works great up to the line where I try to dynamically reference my new arrays. What am I doing wrong and how can I fix it?

The error text is:

('$' + $oc) += $d

~~~~~~~~~ The assignment expression is not valid. The input to an assignment operator must be an object that is able to accept assignments, such as a variable or a property.

CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordException

FullyQualifiedErrorId : InvalidLeftHandSide

I have tried using $($oc), but that didn't work either. If I change it to the name of one of my dynamically created arrays like $user, the code works fine except that it loads everything into the $user array (obviously).

The reason I tried ('$' + $oc) is because this is the only way I could get ISE to output $user.

I also tried ('$' + $oc).add($d) but it appears to be seeing it as a string rather than the array.

Any pointers are appreciated.

briantist · Accepted Answer · 2017-06-14 14:54:50Z

3

Use the Get-Variable and Set-Variable cmdlets:

$curVal = Get-Variable -Name $oc -ValueOnly
Set-Variable -Name $oc -Value ($curVal+$d)

But note that you would be better off building this array in a local variable first, and then assigning it to your "runtime-named" variable once, as these get and set operations are going to be way slower.

edited Jun 14, 2017 at 14:54

answered Jun 14, 2017 at 14:52

briantist

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3 Comments

lightwing Over a year ago

Yep, this seems to have done the trick. Thanks! I'll mark as answer shortly.

briantist Over a year ago

@lightwing thanks but look at Mathias's approach; it's way better for what you're trying to do (I just directly answered your question without actually looking at what you were trying to accomplish).

lightwing Over a year ago

will do. For now, your solution suits me fine.

Mathias R. Jessen · Accepted Answer · 2017-06-14 15:12:15Z

3

Rather than fiddling around with dynamically named variables, I'd use dictionary-type, like for example a hashtable:

# initialize an empty hashtable
$objectsByClass = @{}

# Define list of properties 
$properties = 'samaccountname','canonicalname','objectclass','distinguishedname'

# Retrieve AD objects
$Data = Get-ADObject -SearchBase $sb -filter * -properties $properties | select $properties | sort objectclass,samaccountname

#Populate hashtable
$Data |ForEach-Object {
    if(-not $objectsByClass.ContainsKey($_.objectClass)){
        # Create entry in hashtable
        $objectsByClass[$_.objectClass] = @()
    }
    # Add entry to dictionary
    $objectsByClass[$_.objectClass] += $_
}

Now you can access the items by class name:

$users = $objectsByClass['user']

And you can easily discover all class names:

$classNames = $objectsByClass.Keys

As briantist points out, you can also have Group-Object build the hashtable for you if the above gets too verbose:

$objectsByClass = $Data |Group-Object objectClass -AsHashTable

edited Jun 14, 2017 at 15:12

answered Jun 14, 2017 at 15:05

Mathias R. Jessen

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5 Comments

briantist Over a year ago

This is nicer, yeah. Could we also do this whole thing by just doing $Data | Group-Object -Property objectClass -AsHashTable? :-p

Mathias R. Jessen Over a year ago

@briantist I contemplated using Group-Object but it made my answer look so short and puny xD

briantist Over a year ago

On the contrary it would make it look amazing. Besides sidestepping the original problem, you'd reduce all the code demonstrating it down to a single pipeline!

lightwing Over a year ago

Thanks Mathias, for your input. I have to educate myself more on dictionary types and hashtables, before I'd be comfortable going that route. My current skill level is somewhere between novice and "I can break that." lol I have no doubt this is an excellent answer!

Mathias R. Jessen Over a year ago

@lightwing Trust me, dynamically named variables will have you run in to brokenness faster than you can imagine ;-) Seriously though, just keep breaking shit and it'll come, happy learning! :-)

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