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

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`.)

This should work.

$foo = someFunction 2>$null

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.

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

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 *.*" } }

Recently, I had to shut up powershell on a Linux host, this wasn't that obvious to figure out. After back and forth I found out that wrapping a command in `$( )` and adding a explicit redirection after the wrapper works.

Anything else I tried, wouldn't - I still don't know why since the PowerShell Docs are of desirable quality (and full of inconsistency...)

To import all modules on startup, I added the following. This produced some stderr output by powershell that couldnt be put to rest by `ErrorAction` or redirection without using the wrapping...

If anyone could elaborate on why's that would be very appreciated.
```
# import installed modules on launch
$PsMods = $(Get-InstalledModule);
$($PsMods.forEach({ Import-Module -Name $_.Name -ErrorAction Ignore })) *> /dev/null
```

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

---

**ADDENDUM:**

Please note that (Windows) powershell has many more streams than a linux based OS. Here's the [list from MS docs](

[To see links please register here]

):

[![enter image description here][1]][1]

Thus you can redirect *all* streams using the wildcard with `*>$null`, and you can also use a file instead of `$null`.

[1]: