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How to use a text file as input for a scriptblock - working directory in background jobs

I have been given the task to write a PS script that will, from a list of machines in a text file:

  1. Output the IP address of the machine
  2. Get the version of the SCCM client on the machine
  3. Produce a GPResult HTMl file OR
  4. Indicate that the machine is offline

With a final stipulation of running the script in the background (Job)

I have the scriptblock that will do all of these things, and even have the output formatted like I want. What I cannot seem to do, is get the scriptblock to call the source file from within the same directory as the script. I realize that I could simply hard-code the directories, but I want to be able to run this on any machine, in any directory, as I will need to use the script in multiple locations.

Any suggestions?

Code is as follows (Note: I am in the middle of trying stuff I gathered from other articles, so it has a fragment or two in it [most recent attempt was to specify working directory], but the core code is still there. I also had the idea to declare the scriptblock first, like you do with variables in other programming languages, but more for readability than anything else):

 # List of commands to process in job
$ScrptBlk = {
param($wrkngdir)

Get-Content Hostnames.txt | ForEach-Object {
 # Check to see if Host is online
IF ( Test-Connection $_ -count 1 -Quiet) {
  # Get IP address, extracting only IP value
$addr = (test-connection $_ -count 1).IPV4Address
 # Get SCCM version
$sccm = (Get-WmiObject -NameSpace Root\CCM -Class Sms_Client).ClientVersion
 # Generate GPResult HTML file 
Get-GPResultantSetOfPolicy -computer $_.name -reporttype HTML -path ".\GPRes\$_ GPResults.html"}
ELSE {
  $addr = "Offline"
  $sccm = " "} 
  $tbl = New-Object psobject -Property @{
    Computername = $_
    IPV4Address = $addr
    SCCM_Version = $sccm}}}
 # Create (or clear) output file
Echo "" > OnlineCheckResults.txt
 # Create subdirectory, if it does not exist
IF (-Not (Get-Item .\GPRes)) { New-Item -ItemType dir ".\GPRes" }
 # Get current working directory
$wrkngdir = $PSScriptRoot
 # Execute script
Start-Job -name "OnlineCheck" -ScriptBlock $ScrptBlk -ArgumentList $wrkngdir
 # Let job run
Wait-Job OnlineCheck
 # Get results of job
$results = Receive-Job OnlineCheck
 # Output results to file
$results >> OnlineCheckResults.txt | FT Computername,IPV4Address,SCCM_Version

I appreciate any help you may have to offer.

Cheers.

~DavidM~

EDIT

Thanks for all the help. Setting the working directory works, but I am now getting a new error. It has no line reference, so I am not sure where the problem might be. New code below. I have moved the sriptblock to the bottom, so it is separate from the rest of the code. I thought that might be a bit tidier. I do apologize for my earlier code formatting. I will attempt to do better with the new example.

     # Store working directory
$getwkdir = $PWD.Path
     # Create (or clear) output file
Write-Output "" > OnlineCheckResults.txt
     # Create subdirectory, if it does not exist. Delete and recreate if it does
IF (Get-Item .\GPRes) {
  Remove-Item -ItemType dir "GPRes" 
  New-Item -ItemType dir "GPRes"}
ELSE{
  New-Item -ItemType dir "GPRes"}
     # Start the job
Start-Job -name "OnlineCheck" -ScriptBlock $ScrptBlk -ArgumentList $getwkdir
     # Let job run
Wait-Job OnlineCheck
     # Get results of job
$results = Receive-Job OnlineCheck
     # Output results to file
$results >> OnlineCheckResults.txt | FT Computername,IPV4Address,SCCM_Version

$ScrptBlk = {
  param($wrkngdir)
  Set-Location $wrkngdir
  Get-Content Hostnames.txt | ForEach-Object {
  IF ( Test-Connection $_ -count 1 -Quiet) {
     # Get IP address, extracting only IP value
    $addr = (test-connection $_ -count 1).IPV4Address
     # Get SCCM version
    $sccm = (Get-WmiObject -NameSpace Root\CCM -Class Sms_Client).ClientVersion 
    Get-GPResultantSetOfPolicy -computer $_.name -reporttype HTML -path ".\GPRes\$_ GPResults.html"}
 ELSE {
    $addr = "Offline"
    $sccm = " "} 
$tbl = New-Object psobject -Property @{
  Computername = $_
  IPV4Address = $addr
  SCCM_Version = $sccm}}}

Error text: Cannot validate argument on parameter 'ComputerName'. The argument is null or empty. Provide an argument that is not null or empty, and then try the command again. + CategoryInfo : InvalidData: (:) [Test-Connection], ParameterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationError,Microsoft.PowerShell.Commands.TestConnectionCommand + PSComputerName : localhost

Solution

  • As Theo observes, you're on the right track by trying to pass the desired working directory to the script block via -ArgumentList $wrkngdir, but you're then not using that argument inside your script block.

    All it takes is to use Set-Location at the start of your script block to switch to the working directory that was passed:

    $ScrptBlk = {
  param($wrkngdir)
  
  # Change to the specified working dir.
  Set-Location $wrkngdir

  # ... Get-Content Hostnames.txt | ... 

}

# Start the job and pass the directory in which this script is located as the working dir.
Start-Job -name "OnlineCheck" -ScriptBlock $ScrptBlk -ArgumentList $PSScriptRoot

    In PSv3+, you can simplify the solution by using the $using: scope, which allows you to reference variables in the caller's scope directly; here's a simplified example, which you can run directly from the prompt (I'm using $PWD as the desired working dir., because $PSScriptRoot isn't defined at the prompt (in the global scope)):

    Start-Job -ScriptBlock { Set-Location $using:PWD; Get-Location } |
  Receive-Job -Wait -AutoRemove

    If you invoke the above command from, say, C:\tmp, the output will reflect that path too, proving that the background job ran in the same working directory as the caller.

    Working directories in PowerShell background jobs:

    • Before PowerShell 7.0, starting background jobs with Start-Job uses the directory returned by [environment]::GetFolderPath('MyDocuments') as the initial working directory, which on Windows is typically $HOME\Documents, whereas it is just $HOME on Unix-like platforms (in PowerShell Core).

      • Setting the working dir. for the background job via Start-Job's -InitializationScript script-block argument via a $using: reference - e.g., Start-Job -InitializationScript { $using:PWD } { ... } should work, but doesn't in Windows PowerShell v5.1 / PowerShell [Core] 6.x, due to a bug (the bug is still present in PowerShell 7.0, but there you can use -WorkingDirectory).

    • In PowerShell (Core) 7+, Start-Job now sensibly defaults to the caller's working directory and also supports a -WorkingDirectory parameter to simplify specifying a working directory.

    • In PowerShell (Core) 6+ you can alternatively start background jobs with a post-positional & - the same way that POSIX-like shells such as bash do - in which case the caller's working directory is inherited; e.g.:

        # PS Core only:
  # Outputs the caller's working dir., proving that the background job 
  # inherited the caller's working dir.
  (Get-Location &) | Receive-Job -Wait -AutoRemove