Suppressing error messages in PowerShell ErrorVariable - powershell

Question

Using the snippet below, I'm trying to find a way to suppress the "Attempted to divide by zero" error, and be left with just the custom error message in $err. I've tried combinations of try/catch, Invoke-Command/Expression, redirecting 2>$null, but in every case the error stream still contains the "attempted to divide by zero" message.
function func1 {
[CmdletBinding()]
param()
func2 -ErrorAction SilentlyContinue -ErrorVariable er
if ($er.Count -ge 1) {
Write-Error -Message "Custom error message!"
}
}
function func2 {
[CmdletBinding()]
param()
1/0
}
func1 -ErrorAction SilentlyContinue -ErrorVariable err
$err
populates $err with two items:
Attempted to divide by zero.
At line:15 char:3
+ 1/0
+ ~~~
+ CategoryInfo : NotSpecified: (:) [], RuntimeException
+ FullyQualifiedErrorId : RuntimeException
func1 : Custom error message!
At line:18 char:1
+ func1 -ErrorAction SilentlyContinue -ErrorVariable err
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : NotSpecified: (:) [Write-Error], WriteErrorException
+ FullyQualifiedErrorId : Microsoft.PowerShell.Commands.WriteErrorException,func1
Thanks so much for your thoughts!

Answer 1

Unfortunately the solution is somewhat tricky, because the error that occurs in func2 is invariably recorded in the $err variable passed to -ErrorVariable in the func1 invocation, and is already stored there when the func2 call returns.
Therefore you need to manually remove it:
Replace:
if ($er.Count -ge 1) {
Write-Error -Message "Custom error message!"
}
with:
if ($er.Count -ge 1) {
if ($PSBoundParameters.ContainsKey('ErrorVariable')) {
# Remove the most recently added error from the $err variable.
$PSCmdlet.GetVariableValue($PSBoundParameters['ErrorVariable']).RemoveAt(0)
}
Write-Error -Message "Custom error message!"
}
The automatic $PSBoundParameters variable allows you to check if the common -ErrorAction parameter was specified and with what value (i.e., what target variable name).
The automatic $PSCmdlet variable's .GetVariableValue() method allows access to variables defined in the caller's scope, which enables retrieving the target variable value, which is a [System.Collections.ArrayList] instance whose .RemoveAt() method can be called to remove the most recently added error, which is at index 0.
Asides:
1/0 causes a statement-terminating error, whereas the common -ErrorAction parameter only acts on non-terminating errors (to catch terminating errors you need try / catch). However, because this statement-terminating error occurs inside a function, execution inside that function (potentially) continues, and to the caller the error is in effect a non-terminating one.
For a comprehensive overview of PowerShell's bewilderingly complex error handling, see GitHub docs issue #1583.