Using a Queue instead of a Recursion

Rather than calling functions recursively, you may at times want to use a Queue object that you can load with fresh tasks while you are unloading things that you have already processed.

Lee Holmes has recently posted the below sample which searches an entire filesystem folder tree without recursive calls:

# create a new queue
$dirs = [System.Collections.Queue]::new()

# add an initial path to the queue
# any folder path in the queue will later be processed
$dirs.Enqueue('c:windows')

# process all elements on the queue until all are taken
While ($current = $dirs.Dequeue())
{
    # find subfolders of current folder, and if present,
    # add them all to the queue
    try
    {
        foreach ($_ in [IO.Directory]::GetDirectories($current))
        {
                $dirs.Enqueue($_)
        }
    } catch {}

    try
    {
        # find all files in the folder currently processed
        [IO.Directory]::GetFiles($current, "*.exe") 
        [IO.Directory]::GetFiles($current, "*.ps1") 
    } catch { }
} 

The try-catch blocks are required because of the .NET methods used which raise exceptions when you do not have access privileges to files or folders.


psconf.eu – PowerShell Conference EU 2019 – June 4-7, Hannover Germany – visit www.psconf.eu There aren’t too many trainings around for experienced PowerShell scripters where you really still learn something new. But there’s one place you don’t want to miss: PowerShell Conference EU – with 40 renown international speakers including PowerShell team members and MVPs, plus 350 professional and creative PowerShell scripters. Registration is open at www.psconf.eu, and the full 3-track 4-days agenda becomes available soon. Once a year it’s just a smart move to come together, update know-how, learn about security and mitigations, and bring home fresh ideas and authoritative guidance. We’d sure love to see and hear from you!

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Finding Service Privileges

Get-Service can provide basic information about Windows services but won’t list the required privileges. Here is a small PowerShell function that accepts a service name and returns the service privileges:

function Get-ServicePrivilege
{
    
    param
    (
        [Parameter(Mandatory)]
        [string]
        $ServiceName
    )
    
    # find the service
    $Service = @(Get-Service -Name $ServiceName -ErrorAction Silent)
    # bail out if there is no such service
    if ($Service.Count -ne 1) 
    { 
        Write-Warning "$ServiceName unknown."
        return
    }
    
    # read the service privileges from registry
    $Path = 'HKLM:SYSTEMCurrentControlSetServices' +  $service.Name
    $Privs = Get-ItemProperty -Path $Path -Name RequiredPrivileges

    # output in custom object
    [PSCustomObject]@{
        ServiceName = $Service.Name
        DisplayName = $Service.DisplayName
        Privileges = $privs.RequiredPrivileges
    }
}
 
PS C:> Get-ServicePrivilege spooler

ServiceName DisplayName        Privileges                                                                            
----------- -----------        ----------                                                                            
spooler     Druckwarteschlange {SeTcbPrivilege, SeImpersonatePrivilege, SeAuditPrivilege, SeChangeNotifyPrivilege...}



PS C:> Get-ServicePrivilege XboxGipSvc

ServiceName DisplayName                       Privileges                                                                                
----------- -----------                       ----------                                                                                
XboxGipSvc  Xbox Accessory Management Service {SeTcbPrivilege, SeImpersonatePrivilege, SeChangeNotifyPrivilege, SeCreateGlobalPrivilege} 
 

psconf.eu – PowerShell Conference EU 2019 – June 4-7, Hannover Germany – visit www.psconf.eu There aren’t too many trainings around for experienced PowerShell scripters where you really still learn something new. But there’s one place you don’t want to miss: PowerShell Conference EU – with 40 renown international speakers including PowerShell team members and MVPs, plus 350 professional and creative PowerShell scripters. Registration is open at www.psconf.eu, and the full 3-track 4-days agenda becomes available soon. Once a year it’s just a smart move to come together, update know-how, learn about security and mitigations, and bring home fresh ideas and authoritative guidance. We’d sure love to see and hear from you!

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Using Variable Breakpoints (Part 2)

In the previous tip we examined Set-PSBreakpoint to create dynamic variable breakpoints in PowerShell. We showed how a breakpoint can trigger when a variable changes.

However, what if you want to monitor the change of object properties? Let’s assume you want to monitor the size of an array, and break into the debugger when it grows too large.

In this scenario, the PowerShell variable never changes. It is the object inside the variable that changes. Which is why you need a “Read” mode breakpoint rather than a “Write” mode breakpoint:

# break when $array’s length is greater than 10
Set-PSBreakpoint -Variable array -Action { if ($array.Length -gt 10) { break }} -Mode Read -Script $PSCommandPath

$array = @()
do
{
    $number = Get-Random -Minimum -20 -Maximum 20
    "Adding $number to $($array.count) elements"
    $array += $number
    
} while ($true)

This script breaks into the debugger once the array in $array has more than 10 elements. Don’t forget to press SHIFT+F5 to exit the debugger.


psconf.eu – PowerShell Conference EU 2019 – June 4-7, Hannover Germany – visit www.psconf.eu There aren’t too many trainings around for experienced PowerShell scripters where you really still learn something new. But there’s one place you don’t want to miss: PowerShell Conference EU – with 40 renown international speakers including PowerShell team members and MVPs, plus 350 professional and creative PowerShell scripters. Registration is open at www.psconf.eu, and the full 3-track 4-days agenda becomes available soon. Once a year it’s just a smart move to come together, update know-how, learn about security and mitigations, and bring home fresh ideas and authoritative guidance. We’d sure love to see and hear from you!

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Using Variable Breakpoints (Part 1)

For debugging, variable breakpoints can be of invaluable help. They break into the debugger once a variable changes. If you know that a variable hits a certain value (or a NULL value) when bad things happen, you can make sure the debugger kicks in just then.

The example below illustrates how to use variable breakpoints. It is best to define them at the top of your script because that way you can use $PSCommandPath to find out the actual script file path that is required for breakpoints to work:

# initialize variable breakpoints (once)
# break when $a is greater than 10
Set-PSBreakpoint -Variable a -Action { if ($a -gt 10) { break }} -Mode Write -Script $PSCommandPath

# run the code to debug
do
{
    $a = Get-Random -Minimum -20 -Maximum 20
    "Drawing: $a"
} while ($true)

Make sure you save the code to a script file before you execute it: debugging always requires a physical file.

As you’ll see, the debugger kicks in whenever $a receives a value greater than 10. You can continue with the command “exit”, view all debugger options with “?”, and stop by pressing SHIFT+F4.

To remove all breakpoints, run this:

 
PS C:> Get-PSBreakpoint | Remove-PSBreakpoint
 

psconf.eu – PowerShell Conference EU 2019 – June 4-7, Hannover Germany – visit www.psconf.eu There aren’t too many trainings around for experienced PowerShell scripters where you really still learn something new. But there’s one place you don’t want to miss: PowerShell Conference EU – with 40 renown international speakers including PowerShell team members and MVPs, plus 350 professional and creative PowerShell scripters. Registration is open at www.psconf.eu, and the full 3-track 4-days agenda becomes available soon. Once a year it’s just a smart move to come together, update know-how, learn about security and mitigations, and bring home fresh ideas and authoritative guidance. We’d sure love to see and hear from you!

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