Adding each item from for loop to csv file - powershell

Question

I am trying to use power shell to determine whether a server has a particular patch installed based on the KB and if not append the name to a csv. my input file has system names so I want to export that system name if it does not find the patch installed.
here is what i have so far. The export to csv part does not seem to work.
forEach-Object{
try{
$status = wmic /node:#sys.csv qfe list full /format:table | findstr /i $kb_number
if(!$status){
$output_file = New-Item C:\temp\$kb_number.csv -ItemType File
export-csv $output_file -append -Force
}
else{
write-output $status
}
}
catch{
$error_message = $_.Exception.Message
#write-output "the error message is" $error_message
write-output "Could not find any system with this patch installed."
}
}

Answer 1

Why your code might be failing
We don't see where you're setting the values of #sys.csv or $kb_number in the code you shared. Either of those could be throwing you off.
But the real issue is Export-Csv. For one, you're making a new CSV with every iteration of the loop. And for two, you have to pass in some item for the cmdlet to export as a CSV. Right now, you're only providing these values.
$output_file = New-Item C:\temp\$kb_number.csv -ItemType File
Export-csv -Path $output_file -append -Force
Export-Csv requires an input object. You're not giving it one now.
What do you want to export? If you just want a list of computers without a patch, do this instead.
if(-not(Test-path C:\temp\$kb_number.csv)){
#if file doesn't exist, make it
$output_file = New-Item C:\temp\$kb_number.txt -ItemType File
}
#adds computer name if it doesn't have the patch
Add-Content -Path $output_file -Value $computer
General Suggestions
Instead of using ForEach-Object, you might find it's easier to debug if you use a ForEach loop like this.
$computers = Get-Content C:\pathTo\Your\ComputerList.txt
ForEach($computer in $computers){
}
One additional source of trouble is that your code is using older dos commands in WMIC and then tries to use PowerShell to store the records. You don't need to do this and can make it easier on yourself if you swap out the calls to wmic for Get-WmiObject or Get-CimInstance, the PowerShell native versions of the commands.
To do that, change this line:
wmic /node:#sys.csv qfe list full /format:table | findstr /i $kb_number
translates into
$kb_number = "KB4576484"
Get-CimInstance Win32_QuickFixEngineering -Filter "HotfixID = '$kb_number'" -ComputerName $computer
Source Description HotFixID InstalledBy InstalledOn
------ ----------- -------- ----------- -----------
Update KB4576484 NT AUTHORITY\SYSTEM 9/14/2020 12:00:00 AM
You can store the output of that in a variable and then call Export-Csv on it and that should work.
When in doubt, remove the filter part and just get it working to export all patches to a csv. Then add complexity by adding back the filtering statements.