Filtering based on calculated properties

Hi guys,

I have a new problem, where I got stuck:
I am generating a huge csv report, where I would like to remove a lot of rows. But there are so many, that Excel can’t handle them. So, I thought I might leave them out directly when generating the report.
So, here is a simplified example of what I do:

dir C:\ -recurse | Select Name,@{n=“Size”;e={$.Length / 1MB}}

Now, how can I filter the results, so that I get only the files with the new property “Size” larger than 20 MB? The filter must look for the Size Property, not $
Or even more simplified: Can I apply “Where” after “Select”? I couldn’t manage to do it.

Sure, you can, but you may find that you get better performance with filtering first, then adding the calculated property. Either of these should work:

dir C:\ -recurse | Where-Object { $_.Length -gt 20MB } | Select Name,@{n="Size";e={$_.Length / 1MB}}

dir C:\ -recurse | Select Name,@{n="Size";e={$_.Length / 1MB}} | Where-Object { $_.Size -gt 20 }

I tested it today. Well, the above mentioned example works indeed, but the original one, which is a bit more complex fails to do the filtering.
So, here is the actual script (I only changed the domain name):

Get-ADComputer -Filter * -SearchBase "DC=fabrikam,DC=com" -Properties IntDSFeedback | where {$_.enabled -eq "True"} | Select Name,DistinguishedName,@{n="Bitlocker";e={$_.IntDSFeedback | Select-String "##Bitlocker.Platform=laptop"}},@{n="RK";e={Get-ADObject -Filter * -SearchBase $_.distinguishedname | where {$_.objectclass -eq "msFVE-RecoveryInformation"}}} | where {$_.Bitlocker -ne ""} | Export-Csv D:\laptops.csv

That IntDSFeedback property is a custom property, which contains an array of strings and I only wanted to get those PCs, where that string existed.
The bold part of the code was the one not working --> the exported csv file also contained PCs where the bitlocker property was empty.

Well, it turned out that the part which created me problems was the comparison: “-ne” didn’t work --> it only worked with “-notlike”.

My final command looks like this:

Get-ADComputer -Filter * -SearchBase “DC=fabrikam,DC=com” -Properties IntDSFeedback |
where {($.enabled -eq “True”) -and (($.IntDSFeedback | Select-String “##Bitlocker.Platform=laptop”) -notlike “”)} |
Select Name,DistinguishedName,@{n=“Bitlocker”;e={$.IntDSFeedback | Select-String “##Bitlocker.Platform=laptop”}},@{n=“RK”;e={Get-ADObject -Filter * -SearchBase $.distinguishedname |
where {$_.objectclass -eq “msFVE-RecoveryInformation”}}} |
Export-Csv D:\laptops.csv

And yes, indeed, I got a great performance improvement by applying the filter as early as possible, even though it didn’t look very pretty :slight_smile:
Thanks Dave!

The problem is your use of Select-String. It either returns null (if no matches were found), or one or more Microsoft.PowerShell.Commands.MatchInfo object (if one or more matches were found.) In both cases, $_.BitLocker -ne “” will evaluate to True:

$null -ne ""

When you used the -notlike operator, what you’ve actually done is casted your result from Select-String to a string. $null becomes the empty string, and MatchInfo objects basically display the string. You could have done it a little more explicitly like this. The expression for the BitLocker property could be written as:

$_.IntDSFeedback | Select-String "##Bitlocker.Platform=laptop" | Select -ExpandProperty Line -First 1

This will result in a value of $null if no matches were found, and a String if the pattern was found. In the Where-Object call, you could do this:

where { $_.Bitlocker }

# Or

where { -not [string]::IsNullOrEmpty($_.BitLocker) }

It’s up to you which one you find to be more clear. $null always evaluates to $false in a boolean expression, as do empty strings (and zero for numeric types, $false boolean variables, etc.) Any non-empty string will be $true.