Speed up the processing of my PowerShell script

When your script takes several minutes to process 40 rows, there something more going on than re-reading a file every loop iteration.

From what I can gather you're only making one network call by invoking

gwmi win32_operatingsystem -computername $hostname -ea silentlycontinue

I suspect that this command is taking several seconds to complete, and is making your script slow. You can test this by seeing how long it takes to only invoke this command for all known hostnames, but I think it will be pretty much the same as the running time of your entire script.

I wouldn't know of a faster way to determine the OS version, but I can imagine that this information doesn't change every day, so maybe you could cache this information and have it refreshed on a per-day basis?

-- Edit: As David Martin pointed out, a better option might be to try to make these calls parallel. And apparently, Powershell has support for that through the ForEach -Parallel command.

I looked over the your code and here's what I deduced:

Section One

You have one function with conditional logic

I see nothing wrong with this. It's simple and standard.

function Get-OS ([string]$hostname) {
    $os = "offline"

    gwmi win32_operatingsystem -computername $hostname -ea silentlycontinue | ForEach-Object {
        if($_.Version.ToString().StartsWith("6.1")) {
            $os = "Windows 7"
        } elseif ($_.Version.ToString().StartsWith("5.1")){
            $os = "Windows XP"
        } else {
            $os = "N/A"
        }
    } > $null

    return $os
}

Section Two

You have two foreach loops which read a CSV file from disk and convert the CSV file into an object[] array while looping through each object in that array.

The first foreach loop contains conditional logic. I think this is fine but it could be faster if you imported the CSV into memory before passing it to the pipeline/foreach loop.

Import-CSV C:\RDC\apps.csv | ForEach-Object {
    $appname = $_.appname.ToLower()
    $os = $_.os.ToLower()
    $lob = $_.lob.ToLower()
    $location = $_.location.ToLower()

    if ($Applications.Keys -notcontains $appname) {
        $WindowsOS=@{}

        # hashtable for windows xp and windows 7 applications
        $WindowsOS["windows xp"]=@{}
        $WindowsOS["windows 7"]=@{}
        $Applications[$appname]=$WindowsOS
    } 

    if ($Applications[$appname][$os].Keys -notcontains $lob) {
        $Applications[$appname][$os][$lob]=@()
    }

    if ($Applications[$appname][$os][$lob].Keys -notcontains $location) {
        $Applications[$appname][$os][$lob]+=$location
    }
}

Section Three

The second foreach loop contains:

• another foreach loop
  • which contains conditional logic
    • which contains another foreach loop

Once again, you should read the CSV into memory(variable) before passing it to the loop.

The second thing I think you need to do here is either reduce the nesting by writing different code to do the same job, or at the very least separate the inside foreach loop from the if statement somehow.

Import-CSV C:\RDC\hosts.csv | ForEach-Object {
    $Properties = @{}
    $Properties["hostname"]=$_.hostname.ToLower()
    $Properties["lob"]=$_.type.ToLower()
    $Properties["os"]=Get-OS $Properties["hostname"]

    $Applications.Keys | ForEach-Object {
        $currAppName = $_
        $Properties[$currAppName]=$false;

        if ($Applications[$currAppName].Keys -contains $Properties["os"] -and $Applications[$currAppName][$Properties["os"]].Keys -contains $Properties["lob"]) {
            $Applications[$currAppName][$Properties["os"]][$Properties["lob"]] | ForEach-Object {
                $Properties[$currAppName]=$Properties[$currAppName] -or (Test-Path "\\$($Properties["hostname"])\$($_)")
            }
        }
    }

    $HostObject = New-Object PSObject -Property $Properties
    $ComputerObjects += $HostObject
}

Final Comments

Those are the main parts of your script that are going to take the most time.

You can also try wrapping each section in Measure-Command {} to see which section is taking up all/most of the time.

You can speed it up by multi-threading the Get-WMIObject (but don't try to do it with background jobs). Get-WMIObject will multi-thread itself if you pass it multiple computer names. It will take some re-factoring but you should collect all the host names first, then pass that collection to Get-WMIObject all at once. Sort the results into a hash table of hostname/os and then foreach through your csv, going back to the hash table to get the os for each host.

You can also speed up your script by not using foreach. this will invoke the whole object before you run the loop. using For($i=0; $i -lt $csv.count; $i){Commands} if you are only looking for certain data you should but it in a function and return the value inside the loop instead of waiting for it to finish.

If you you are working with a sorted csv file. you can jump down to a certain value of your csv by checking the input and setting $i to a certain line.

Im currently working on a project myself where i know Desktops shows up after line 15000. I then tell the loop $i = 15000; $i -lt $csv.count;$i++ this is basicly useless when working with small files, but with bigger files like in my case this is actully usefull.