Powershell - Select-String -Quiet not working as intended?

Question

So I am writing a powershell script that, among other things, checks to see if you are in an Exchange Distribution Group, and adds you if necessary.

One thing that is making it tricky is, the script is getting its data from an "unreliable" source. That is, I can't guarantee that I have a username to even check against.

So, I need to check in the case of an empty string. I have my username stored in a variable $tempUserName which is just a String, and the name of a Distribution List stored in $DefaultMobileDL. For other reasons I won't get into, I can't do if {} else {} statements, I can only do if statements. It is very stupid, I know.

OK, so here is what I have:

if (-not [string]::IsNullOrEmpty($tempUsername)) { 
    $MembersOfDLDefault = Get-DistributionGroupMember "$DefaultMobileDL" -ResultSize Unlimited |
        Select -Expand sAMAccountName | 
        Select-String -pattern "$tempUsername" -SimpleMatch -Quiet 
}
if ([string]::IsNullOrEmpty($tempUsername)) { $MembersOfDLDefault = $false }

# bug testing...
Write-Host "username: `"$tempUsername`" , MembersOfDLDefault: `"$MembersOfDLDefault`""

if ($MembersOfDLDefault -eq $false) {
  # User is not a member of $DefaultMobileDL, try adding them
  # ... more code here ...
}
if ($MembersOfDLDefault -eq $true) {
  # User is already a member of the $DefaultMobileDL
  # ... again, more code ...
}

That code block is in a foreach loop, and since I was having problems with variables values being passed on after each iteration, at the very end of my code I clear several variables, but for this instance the one line that matters is:

Clear-Variable MembersOfDLDefault

Now if I'm reading the documentation right, Select-String -Quiet should return True if the item was found, and False if it wasn't.

However, that is not the results that I'm getting. Here is what happens when I run the code (in this run, I have 3 usernames I happen to be testing, one of which (the third one) is an empty string):

username: "smithj" , MembersOfDLDefault: ""
username: "doej" , MembersOfDLDefault: "True"
username: "" , MembersOfDLDefault: "False"

As you can see, the first time the code is run, $MembersOfDLDefault doesn't get set to anything!

I know I'm just missing something stupid, but I've been staring at this code for too long, need some fresh eyes on it. Anything obvious that I'm missing or overlooking?

Thanks in advance.

Technically I'm running this from the Exchange Management Shell, and not from Powershell directly, although I don't think that should matter

Wouldn't it be a lot simpler to use -contains to test for name in the group membership list? — mjolinor, May 23 '14 at 13:59
You mean `$MembersOfDLDefault = Get-DistributionGroupMember "$DefaultMobileDL" -ResultSize Unlimited | Select -Expand sAMAccountName` then later have `if ($MembersOfDLDefault -contains "$tempUsername")`? I originally had that, but Powershell complained because the `Get-DistributionGroupMember` function was returning a **lot** of data, so it suggested I try a pipe to reduce the variable size. — romellem, May 23 '14 at 14:50
If the distribution group is that big, it sounds like you'd be better off checking the users group memberships for the DL instead of the other way around. — mjolinor, May 23 '14 at 15:23

score 3 · Accepted Answer · answered May 23 '14 at 17:19

It seems like what the documentation says about -quiet and what it actually does are different. The behaviour seems to be that Select-String -quite will return $null when there is no match. To verify this try:

# ~> "xxxHELLOaaa" | Select-String "HELLO" -SimpleMatch -Quiet
True

# ~> "xxxHELLOaaa" | Select-String "HaLLO" -SimpleMatch -Quiet

Either the implementation is incorrect or the documentation is (I can't find any confirmation either way). A simple workaround would be to cast your result to a boolean:

if (-not [string]::IsNullOrEmpty($tempUsername)) { 
    $MembersOfDLDefault = [bool] (Get-DistributionGroupMember "$DefaultMobileDL" -ResultSize Unlimited |
        Select -Expand sAMAccountName | 
        Select-String -pattern "$tempUsername" -SimpleMatch -Quiet )
}

Thank you so much! I'm still getting acclimated to PowerShell so I didn't know you could do explicit casting. That did the trick. — romellem, Jun 05 '14 at 17:26

Powershell - Select-String -Quiet not working as intended?

1 Answers1