(PowerShell) Log Exceptions and Continue (Active Directory Module) - powershell

Question

I'm using New-ADUser and Add-ADGroupMember
If the user already exists or is already in the group then the functions throw exceptions (which are expected and not a problem).
How do I log the exceptions to file and keep going?
Redirection is not working - the exceptions always go to the
console.
-ErrorAction is not working - exceptions still go to the console
Try / Catch works, but execution stops and the rest of the commands don't run
I can do a Try / Catch for every single statment, but that seems
ridiculous

Answer 1

You can combine -ErrorAction SilentlyContinue with -ErrorVariable:
$e = $null
New-ADUser iExist -ErrorAction SilentlyContinue -ErrorVariable e
$e # contains the error
You can also use the built in $Error variable, which is a circular buffer holding all the errors.
$ErrorPreference = SilentlyContinue # I don't like this personally
New-ADUser iExist
Add-ADGroupMember iExist iForgotTheParameters
$Error[0] # The Add-ADGroupMember error
$Error[1] # The New-ADUser error
So you could set your $ErrorPreference, do a bunch of commands, and at the end of it all, do something like $Error | Out-File -Path errors.txt.
Have a look at PowerShell Error Handling and Why You Should Care for more ideas.

Answer 2

The simplest way to accomplish this is probably using the trap construct:
function Test-Trap{
trap {
$_ | Out-String | Out-File C:\path\to\errors.txt -Append
}
Get-ADUser -NoSuchParam "argument"
Write-Host "Show must go on"
nonexistingcommand
Write-Host "Still executing"
}
When you call Test-Trap, you'll see that after the error has been written to the console, the trap is executed, and the rest of the execution flow is resumed:
And the error record output as it would normally appear on screen (courtesy of Out-String) has been saved to the file:
You could add cool features like timestamps and stack traces to your trap:
function Test-Trap{
trap {
$LogPath = "C:\path\to\errors.txt"
$ErrorCount = $ErrorCount + 1
$("[Error {0} trapped {1}]:" -f $ErrorCount,(Get-Date -Format "dd/MM/yyyy HH:mm:ss.fff")) | Out-File $LogPath -Append
$_ | Out-String | Out-File $LogPath -Append
if(($st = $_.Exception.Stacktrace)){ $st |Out-File $LogPath -Append }
$("[Error {0} logged]" -f $ErrorCount)| Out-File $LogPath -Append
}
Provoke-Error -NoSuchParam muhahaha
}