PowerShell Get-Process not working correctly when we have multiple instance of process

Question

I am trying to record CPU and memory utilizations of processes running in my window server using PowerShell. Script is running well but I am not getting anything if Mutiple process are running with same process name. it is throwing error: Method invocation failed because [System.Object[]] does not contain a method named 'op_Division I am getting my process list correctly using this command $processList = Get-Process -Name myMap | Select-Object -ExpandProperty ProcessName

Please help me, here is my code

$processList = Get-Process -Name myMap | Select-Object -ExpandProperty ProcessName
$outputFile = "D:\Users\vin\Performance_Srcipts\output\mymap.csv"
"Timestamp,ProcessName,%CPU,Memory(MB)" | Out-File -FilePath $outputFile
 For ($i = 0; $i -lt 10; $i++) { 
 foreach ($processName in $processList) {
 $process = Get-Process -Name $processName -ErrorAction SilentlyContinue
 
 if ($process) {
 $timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
 $cpu= try { (Get-Counter -Counter "\Process($processName*)\% Processor Time").CounterSamples.CookedValue / (Get-Process -Name $processName).Count } catch { 0 }
 $memory = [math]::Round($process.WorkingSet64 / 1MB, 2)
 "$timestamp,$processName,$cpu,$memory" | Out-File -FilePath $outputFile -Append
 }
 }
 Start-Sleep -Seconds 5 
}
Write-Host "Process monitoring completed. Data saved to $outputFile"

• burnie: You already answered your question by yourself: "...but I am not getting anything if Mutiple process are running with same process name.". Also the error message itself shows [System.Object[]]. $process is an array, so you must do something like $memory = [math]::Round($process[0].WorkingSet64 / 1MB, 2).
• mclayton: Note - it would be an incredibly pathological edge case but if a process name has a comma in it your remaining data for that row will be thrown out by one column. When generating formatted data it’s a good idea to use pre-built cmdlets like Export-Csv or ConvertTo-Csv.

Answer 1

You already answered your question by yourself:

...but I am not getting anything if Mutiple process are running with same process name.

Also the error message itself shows [System.Object[]]. So, $process is an array of objects. You could change your code as follows:

For ($i = 0; $i -lt 10; $i++) { 
 foreach ($processName in $processList) {
 $process = Get-Process -Name $processName -ErrorAction SilentlyContinue
 
 if ($process.Count -gt 0) {
 foreach ($p in $process) {
 $timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
 $cpu = try {
 (Get-Counter -Counter "\Process($processName*)\% Processor Time").
 CounterSamples.CookedValue / (Get-Process -Name $processName).Count
 }
 catch { 0 }
 $memory = [math]::Round($p.WorkingSet64 / 1MB, 2)
 "$timestamp,$processName,$cpu,$memory" |
 Out-File -FilePath $outputFile -Append
 }
 }
 }
 Start-Sleep -Seconds 5 
}

Answer 2

• Using the -Name parameter of Get-Process - i.e. looking for processes by (executable) name - inherently means that it is possible for more than 1 process to match.

• Collecting the output from such a call matching multiple processes in a variable of necessity stores the process-information objects (of type [System.Diagnostics.Process]) in an array (of type [object[]] (in PowerShell terms) aka System.Object[] (in .NET terms)).

• Performing property access such as .WorkingSet64 on such an array results in member-access enumeration, which means that the relevant property values of the array's elements are accessed and also returned as an array (in the case of two or more elements).

• Providing an array as an operator to /, the division operator, isn't supported, which explains the error you saw; only scalar operands work.

  • In other words: $process.WorkingSet64 / 1MB resulted in something like
    @(42, 43) / 1MB, which predictably fails.

---

Here's a streamlined reformulation of your code that avoids the problem, by ensuring that $process only ever refers to a single process at a time:

$outputFile = 'D:\Users\vin\Performance_Srcipts\output\mymap.csv'
'Timestamp,ProcessName,%CPU,Memory(MB)' | Out-File -FilePath $outputFile
& {
 for ($i = 0; $i -lt 10; $i++) { 
 foreach ($process in ($processes = Get-Process -ErrorAction SilentlyContinue -Name myMap)) {
 $timestamp = Get-Date -Format 'yyyy-MM-dd HH:mm:ss'
 $cpu = try { (Get-Counter -Counter "\Process($($process.Name)*)\% Processor Time").CounterSamples.CookedValue / $processes.Count } catch { 0 }
 $memory = [math]::Round($process.WorkingSet64 / 1MB, 2)
 "$timestamp,$processName,$cpu,$memory"
 }
 Start-Sleep -Seconds 5 
 }
} | Out-File -FilePath $outputFile -Append
Write-Host "Process monitoring completed. Data saved to $outputFile"

In general, mclayton's advice about using OO techniques in combination with Export-Csv to produce your CSV file is worth considering too.