Suppressing output from Powershell command

Question

I'm trying to process firewall rules in a powershell script - here is the line I'm using:

$currentRules = get-netfirewallRule -CimSession computer4 -direction Inbound

So this works fine if it returns any rules, returns a collection of some sort which are stored in $currentRules. All good.

the problem arises if get-netfirewallrule doesn't find any matches - I get a helpful

    get-netfirewallRule : computer4: No MSFT_NetFirewallRule objects found with property 'Direction' equal to 'Inbound'.  Verify the value of the property and retry.
At line:1 char:1
+ get-netfirewallRule -CimSession computer4 -direction Inbound | ou ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (Inbound:Direction) [Get-NetFirewallRule], CimJobException
    + FullyQualifiedErrorId : CmdletizationQuery_NotFound_Direction,Get-NetFirewallRule
    + PSComputerName        : computer4

splatted in the middle of my output. I've tried the usual > $null and | out-null, but still the output ends up on my screen. Any ideas how I can stop it displaying this 'useful' message?

thanks,

Jim

Theo · Accepted Answer · 2020-07-10 11:50:45Z

2

Peter Schneiders helpful answer is correct, although you would normally use that when you need the erroraction set for more cmdlets.
If you only want to suppress the error output for this one command, you can also specify parameter -ErrorAction SilentlyContinue to it straight away like:

$currentRules = Get-NetFirewallRule -CimSession computer4 -Direction Inbound -ErrorAction SilentlyContinue

There is also the -ErrorVariable parameter with wich you can have the code capture any exception inside a variable of your own and inspect that later:

$currentRules = Get-NetFirewallRule -CimSession computer4 -Direction Inbound -ErrorAction SilentlyContinue -ErrorVariable MyErrorVar
# display the error if any
$MyErrorVar

Sometimes, a cmdlet outputs an exception eventhough the ErrorAction is set to 'SilentlyContinue'. In these cases you can also use the a try{}..catch{} block. You then need to set the ErrorAction to 'Stop' so also non-terminating errors are directed to the catch block:

try {
    $currentRules = Get-NetFirewallRule -CimSession computer4 -Direction Inbound -ErrorAction Stop
}
catch {
    # write custom message on screen or write to log file or..
    Write-Warning "Failed to get Firewall rules.."
}

answered Jul 10, 2020 at 11:50

Theo

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1 Comment

Jim ReesPotter Over a year ago

Thanks Theo! This has also helped with my error handling issues - Powershell seems very chatty, being able to bag up the chat 9both errors and standard output) and process it in try catch loops seems to work pretty well

Peter Schneider · Accepted Answer · 2020-07-10 10:10:34Z

1

You can set the $ErrorActionPreference variable to "SilentlyContinue"

$eap = $ErrorActionPreference
$ErrorActionPreference = "SilentlyContinue"
1/0
$ErrorActionPreference = $eap

answered Jul 10, 2020 at 10:10

Peter Schneider

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Comments

RetiredGeek · Accepted Answer · 2020-07-12 15:32:44Z

0

Using the Try/Catch construct allows you to trap errors and process them preventing unwanted error messages from appearing in your output.

$GNFArgs = @{CimSession = "computer4"
             Direction  = "Inbound"
             ErrorAction = "Stop"
            }

Try {
      $currentRules = get-netfirewallRule @GNFArgs
    }
Catch {
  #Process error here 
}

HTH

edited Jul 12, 2020 at 15:32

answered Jul 10, 2020 at 11:52

RetiredGeek

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1 Comment

Chris Over a year ago

This is the second of your answers in a row that I've seen in the "low quality posts" queue, probably because you're just dumping code and not explaining it. Please read How to Answer.

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