Redirecting output to $null in PowerShell, but ensuring the variable remains set

Question

I have some code:

$foo = someFunction

This outputs a warning message which I want to redirect to $null:

$foo = someFunction > $null

The problem is that when I do this, while successfully supressing the warning message, it also has the negative side-effect of NOT populating $foo with the result of the function.

How do I redirect the warning to $null, but still keep $foo populated?

Also, how do you redirect both standard output and standard error to null? (In Linux, it's 2>&1.)

What produces the warning message? If you are the author of `someFunction`, you might change it appropriately. — stej, May 04 '11 at 19:30
Actually, in Bourne Shell (Linux), it's `2>/dev/null 1>/dev/null`; The redirect you've shown redirects stderr to the same place as stdout -- which may be `/dev/null`, or may be a regular file. — jpaugh, Dec 13 '16 at 15:17

score 184 · Answer 1 · edited Jul 11 '15 at 22:18

184

I'd prefer this way to redirect standard output (native PowerShell)...

($foo = someFunction) | out-null

But this works too:

($foo = someFunction) > $null

To redirect just standard error after defining $foo with result of "someFunction", do

($foo = someFunction) 2> $null

This is effectively the same as mentioned above.

Or to redirect any standard error messages from "someFunction" and then defining $foo with the result:

$foo = (someFunction 2> $null)

To redirect both you have a few options:

2>&1>$null
2>&1 | out-null

edited Jul 11 '15 at 22:18

Peter Mortensen

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answered Jun 23 '11 at 21:51

J Bills

1,849
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This solution worked for me after I wrapped the statements in {curly braces} instead of (parenthesis). I may be using a newer PS version. – ManEatingCheese Sep 08 '19 at 09:43
1

And if we are creating a background job, we need to quite the job'ing itself: `{ myCommandWithAnyOutput & } | Out-Null` – arberg Sep 28 '19 at 08:10

score 13 · Answer 2 · answered May 04 '11 at 09:49

13

This should work.

 $foo = someFunction 2>$null

answered May 04 '11 at 09:49

ravikanth

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score 10 · Answer 3 · answered Oct 09 '13 at 14:15

10

If it's errors you want to hide you can do it like this

$ErrorActionPreference = "SilentlyContinue"; #This will hide errors
$someObject.SomeFunction();
$ErrorActionPreference = "Continue"; #Turning errors back on

answered Oct 09 '13 at 14:15

Christian Flem

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score 5 · Answer 4 · answered Feb 15 '12 at 14:20

Warning messages should be written using the Write-Warning cmdlet, which allows the warning messages to be suppressed with the -WarningAction parameter or the $WarningPreference automatic variable. A function needs to use CmdletBinding to implement this feature.

function WarningTest {
    [CmdletBinding()]
    param($n)

    Write-Warning "This is a warning message for: $n."
    "Parameter n = $n"
}

$a = WarningTest 'test one' -WarningAction SilentlyContinue

# To turn off warnings for multiple commads,
# use the WarningPreference variable
$WarningPreference = 'SilentlyContinue'
$b = WarningTest 'test two'
$c = WarningTest 'test three'
# Turn messages back on.
$WarningPreference = 'Continue'
$c = WarningTest 'test four'

To make it shorter at the command prompt, you can use -wa 0:

PS> WarningTest 'parameter alias test' -wa 0

Write-Error, Write-Verbose and Write-Debug offer similar functionality for their corresponding types of messages.

Elroy Flynn · Answer 5 · 2019-11-18T16:30:19.323

using a function:

function run_command ($command)
{
    invoke-expression "$command *>$null"
    return $_
}

if (!(run_command "dir *.txt"))
{
    if (!(run_command "dir *.doc"))
    {
        run_command "dir *.*"
    }
}

or if you like one-liners:

function run_command ($command) { invoke-expression "$command  "|out-null; return $_ }

if (!(run_command "dir *.txt")) { if (!(run_command "dir *.doc")) { run_command "dir *.*" } }

Redirecting output to $null in PowerShell, but ensuring the variable remains set

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