Compare-Object on $null array

Question

Is there a way for the Compare-Object cmdlet to anticipate on $Null values?

For example when I'm trying to compare 2 values like this:

Compare-Object -ReferenceObject $Value1 -DifferenceObject $Value2

I commonly get the following error:

Cannot bind argument to parameter 'ReferenceObject' because it is null

My question is: Is there a way to say: if either one of them equals $null ; do something

Cross posting another answer: stackoverflow.com/questions/13504346/… — Craig - MSFT
– Craig - MSFT, Commented Apr 7, 2015 at 17:23

Aaron · Accepted Answer · 2017-08-11 12:09:09Z

24

This accepts null values:

Compare-Object -ReferenceObject @($Value1 | Select-Object) -DifferenceObject @($Value2 | Select-Object)

answered Aug 11, 2017 at 12:09

Aaron

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4 Comments

Jeremy Over a year ago

This works marvelously for what I was looking for. I'm importing from AD, but if the array is null, I error. I want to get the result that object is different from object2 (null) if that is the case. This does it in a simple manor without having to write evaluation cases for objects.

codaamok Over a year ago

I noticed the pipe to Select-Object wasn't necessary in my tests. Can you explain why you used it in your answer?

Aaron Over a year ago

@($null).Count 1 @($null | Select-Object).Count 0

Bram Over a year ago

Thanks for this answer. Could you explain why this works? Is it because Select-Object always returns an object whereas e.g. get-content returns a string of bytes?

mjolinor · Accepted Answer · 2013-03-18 21:58:32Z

5

Help on Compare-object says:

If the reference set or the difference set is null ($null), Compare-Object generates a terminating error.

So your only options would seem to be a trap or try/catch.

answered Mar 18, 2013 at 21:58

mjolinor

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Comments

E.V.I.L. · Accepted Answer · 2013-03-19 20:10:40Z

1

 if($Value1 -eq $NULL){
     return
 }
 Compare-Object -ReferenceObject $Value1 -DifferenceObject $Value2

answered Mar 19, 2013 at 20:10

E.V.I.L.

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2 Comments

Eric J. Over a year ago

This would be a stronger answer if you explain it.

E.V.I.L. Over a year ago

It's just an alternative to try/catch. If the first value is NULL stop. If isn't NULL, you can Compare the Object. I don't know PS good enough to get those try/catch phrases working.

Aaron · Accepted Answer · 2017-08-11 17:14:10Z

1

This does something if null:

if ($Value1 -ne $null -and $Value2 -ne $null) {
    Compare-Object -ReferenceObject $Value1 -DifferenceObject $Value2
}
else {
    #do something
}

answered Aug 11, 2017 at 17:14

Aaron

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David Buck · Accepted Answer · 2020-07-10 23:17:48Z

1

There is a workaround you can use

First, create two empty array object

$reference = @()
$difference = @()

Now

Check your sources array if not null and add them to previously créated array

If( $array1 -ne $null ){ $reference.addrange($array1) 
If($array2 -ne $null) { $diffrence.addrange($array2)

Now you are sure that your reference array and diffirence array are not null even they could be empty, and you can securely do comparaison

Compare-object -referenceObject $reference -differenceObject $difference

edited Jul 10, 2020 at 23:17

David Buck

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answered Jul 10, 2020 at 22:59

pluton1795

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