Tag Archives: -AutoSize

Return Only the Fixed Disks

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Notice: The following post was originally published on another website. As the post is no longer accessible, it is being republished here on tommymaynard.com. The post was originally published on January 15, 2019.

As a part of a recent engagement (with a company you’ve likely heard of), we had some code written and provided to us. In my review of what was provided to scan drives using Windows Defender, I noticed that there were some problems. One, there was an assumption that a computer would only ever have a single optical drive, and two, mapped network drives may have ended up being scanned, as well. Now, I’m not sure if Defender would actually scan a network drive, but I assume it would and don’t really care to find out.

We needed a way to filter out optical drives and network mapped drives regardless of the count of either before we started a Windows Defender scan. I’ll start with the code I used, followed by a second option that occurred more recently — it was a would this work idea. It does, so I’ll explain them both and perhaps we’ll all be better off seeing two different options. Before we get deeper into this, take a look at the output provided by Get-PSDrive (when piped to Format-Table and the AutoSize parameter). Clearly, it’s found a good number of drives on my system.

PS> Get-PSDrive | Format-Table -AutoSize

Name     Used (GB) Free (GB) Provider    Root                      CurrentLocation
----     --------- --------- --------    ----                      ---------------
Alias                        Alias
C           698.18    232.15 FileSystem  C:\                           Users\tommy
Cert                         Certificate \
D                            FileSystem  D:\
E                            FileSystem  E:\
Env                          Environment
Function                     Function
HKCU                         Registry    HKEY_CURRENT_USER
HKLM                         Registry    HKEY_LOCAL_MACHINE
MDI                          FileSystem  \\mydomain.com\data\in...
MDT                          FileSystem  \\mydomain.com\data\to...
I           112.80    352.96 FileSystem  I:\
P             0.15    465.60 FileSystem  P:\
Variable                     Variable
W           676.59    254.92 FileSystem  W:\
WSMan                        WSMan

Now, let’s modify our command and only return our FileSystem drives. Unfortunately, there are a couple of optical drives (although you don’t really know that yet), and two mapped network drives that we don’t want or need in our results.

PS> Get-PSDrive | Format-Table -AutoSize

Name     Used (GB) Free (GB) Provider    Root                      CurrentLocation
----     --------- --------- --------    ----                      ---------------
Alias                        Alias
C           698.18    232.15 FileSystem  C:\                           Users\tommy
Cert                         Certificate \
D                            FileSystem  D:\
E                            FileSystem  E:\
Env                          Environment
Function                     Function
HKCU                         Registry    HKEY_CURRENT_USER
HKLM                         Registry    HKEY_LOCAL_MACHINE
MDI                          FileSystem  \\mydomain.com\data\in...
MDT                          FileSystem  \\mydomain.com\data\to...
I           112.80    352.96 FileSystem  I:\
P             0.15    465.60 FileSystem  P:\
Variable                     Variable
W           676.59    254.92 FileSystem  W:\
WSMan                        WSMan

In this next example, we’ll remove the mapped drives from our results. In the end, we have our fixed drives and the D:\ and E:\ drives that have no used or free space. Perhaps those are the optical drives and there are no actual disks in either one. Before we move past this example, however, let’s get the results of this command into a variable, as well. The $FixedDrives variable is assigned toward the bottom of the below example.

PS> Get-PSDrive -PSProvider FileSystem | Where-Object -Property Root -notlike '\\*' | Format-Table -Autosize

Name     Used (GB) Free (GB) Provider    Root CurrentLocation
----     --------- --------- --------    ---- ---------------
C           698.18    232.15 FileSystem  C:\      Users\tommy
D                            FileSystem  D:\
E                            FileSystem  E:\
I           112.80    352.96 FileSystem  I:\
P             0.15    465.60 FileSystem  P:\
W           676.59    254.92 FileSystem  W:\

PS> $FixedDrives = Get-PSDrive -PSProvider FileSystem | Where-Object -Property Root -notlike '\\*'
PS> # Noticed we removed Format-Table -- that was _only_ there for the onscreen display.

Now, let’s get a hold of our optical drives. Because we’ll need them in a variable, we’ll go ahead and make that assignment in this next example, as well.

PS> Get-WmiObject -Class Win32_CDROMDrive | Format-Table -AutoSize

Caption                           Drive Manufacturer             VolumeName
-------                           ----- ------------             ----------
ASUS DRW-1814BLT ATA Device       D:    (Standard CD-ROM drives)
ELBY CLONEDRIVE SCSI CdRom Device E:    (Standard CD-ROM drives)

PS> $OpticalDrives = Get-WmiObject -Class Win32_CDROMDrive

Now that that’s done — oh look, it is the D:\ and E:\ drives — let’s run a comparison against the fixed drives and optical drives we’ve returned. Again, this first example is how I rewrote the code that was provided to us. Once we’ve seen this, then we’ll try the comparison I considered over some recent weekend. This example compares the Get-PSDrive‘s Root property (with the backslash removed) against the Get-WmiObject‘s Drive property. If they don’t match, it stays. Otherwise, it’s filtered out. As you’ll see, when we assign and return our new $DrivesToTest variable, we can see that our D:\ and E:\ drives — our optical drives — have been removed. Perfect.

PS> $DrivesToTest = ($FixedDrives.Root).TrimEnd('\') | Where-Object {$OpticalDrives.Drive -notcontains $_}
PS> $DrivesToTest
C:
I:
P:
W:

Let’s use our $FixedDrives and $OpticalDrives variables again, but this time with the Compare-Object cmdlet. This was the additional idea I had to determine if we can simplify things even more. As some have noticed — I have not shied away from the fact that I tend to do things the hard way, the first time. In case it makes a difference, and I hope it doesn’t, Compare-Object was first introduced in PowerShell 3.0.

PS> (Compare-Object -ReferenceObject ($FixedDrives.Root).TrimEnd('\') -DifferenceObject $OpticalDrives.Drive).InputObject
C:
I:
P:
W:

Just like that, we’ve got the same results, with less work. Now, I can get back to doing whatever it was before I began reviewing this code. That and our users can safely get to work scanning machines with Windows Defender, without the concern anyone will scan against any number of optical drives, or mapped network drives.

Give your Variable a Description

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When we think of variables in Windows PowerShell, we often only consider two parts: the name of the variable, and the value of the variable. Well, it turns out that those aren’t the only properties; let’s discuss the description property.

I can’t say I’ve ever added a description to a variable until now, but I can think of times, when looking at someone’s code, where I wish I knew the reason why a variable existed. Best practice would indicate we use meaningful names for our variables, so it’s probably safe to assume that the same people that might use a poorly-named variable, probably don’t know or care that variables can have descriptions… but, I digress.

In this first example, we’ll create a new variable using what I’d call the standard method — the equal sign assignment operator.

PS C:\> $a = 12345
PS C:\> $a
12345
PS C:\> Get-Variable a | Select-Object *

Name        : a
Description :
Value       : 12345
Visibility  : Public
Module      :
ModuleName  :
Options     : None
Attributes  : {}

In line 1, we created a new variable, $a, and set its value to the numeric 12345. In the next line, we simply echoed the variable’s value. In line 4, we used the Get-Variable cmdlet and piped it to the Select-Object cmdlet and * so we were able to view all of its properties. If you take a look at the results, you’ll see the description property, and notice that it’s currently blank.

In the next example, we’ll use the Set-Variable cmdlet to modify the variable’s description.

PS C:\> Set-Variable a -Description 'This variable contains a 5-digit number.'
PS C:\> Get-Variable a | Select-Object *

Name        : a
Description : This variable contains a 5-digit number.
Value       : 12345
Visibility  : Public
Module      :
ModuleName  :
Options     : None
Attributes  : {}

PS C:\>

Once we use the Get-Variable cmdlet, and return all the properties again, we can see that our variable now contains a description value. Now, while many user-defined variables, such as we created here, don’t often contain descriptions, many of the automatic and preference variables do — take a look at a segment of the results returned by the next command.

PS C:\> Get-ChildItem variable: | Select-Object Name,Description | Format-Table -AutoSize

Name                       Description
----                       -----------
...
MaximumAliasCount          Maximum number of aliases allowed in a session
MaximumDriveCount          Maximum number of drives allowed in a session
MaximumErrorCount          Maximum number of errors to retain in a session
MaximumFunctionCount       Maximum number of functions allowed in a session
MaximumHistoryCount        Maximum number of history objects to retain in a session
MaximumVariableCount       Maximum number of variables allowed in a session
MyInvocation
NestedPromptLevel          Dictates what type of prompt should be displayed for the current nesting level
...

Well, there you go: something you might not have known about, and something you may never use.