Ubiquitous -OnError {ScriptBlock} parameter

[jpsnover]

Ubiquitous -OnError {Scriptblock} parameter which would take precedence over -ErrorAction and others. The scriptbock would be called on terminating errors and would be called for every non-terminating error. For non-terminating errors, the scriptblock can control whether to STOP or CONTINUE code execution.

This would unify the processing of terminating vs non terminating errors:

# Nonterminating error
Stop-Process foo* -OnError {
     Write-Host "Had an error."
}

# Terminating error
Start-CmdwithTerminatingError -OnError {
      Write-Host "Had an error."
}



# Terminating errors always terminate but now non-terminating errors are controlled by Continue/Break
# Continue  == -ErrorAction Continue
# Break     == -ErrorAction Stop
# -ErrorAction Debug can be achieved by writing a message, doing a Wait-Debugger and then 
# afterwards you can continue or break.
Stop-Process foo* -OnError {
     Write-Host "Had an error. Continuing"
     Continue
}

Stop-Process foo* -OnError {
     Write-Host "Had an error. Stopping"
     Break
}

Stop-Process foo* -OnError {
     Write-Host "Had an error.  Debug this script"
     Wait-Debugger
     if ((Read-Host "Type 'y' to continue") -eq 'y'){
        Continue
     } else {
        Break
     }
}

Start-CmdwithTerminatingError -OnError {
      Write-Host "Had an error. Stopping or Continuing has the same effect"
      Break
}



# scriptblock is run at the botton - you have the full call stack preserved
stop-process foo* -OnError { 
   Write-Host "PSCALLstack is preserved!"
   Get-PSCallstack
}


# The exception is surfaced through $_ the same as with try/catch
Stop-Process foo* -OnError {
    Write-Host "Error stopping: $($_.TargetObject)`n"
}

[felixfbecker]

Really like the idea as there isn't really any good way to handle errors from the error stream. The only way known to me is something like this:

Get-Whatever 2>&1 |
  ForEach-Object {
    if ($_ -is [ErrorRecord]) {
      # handle error
    } else {
      $_
    }
  }

However, the break and continue seem weird to me because this is a scriptblock, not a loop.
Why not continue by default, and break with throw? That would be more intuitive to me

[skycommand]

So, how does it work for distinguishing the error type and acting accordingly? Let's say there is a script in which a file has to be deleted. The Remove-Item command might end with an error when:

1. The file is not found: Well, that's good, right? We wanted the file gone and it is. The script can disregard this and move on.
2. Access to the file is denied: Not good! We wanted the file gone and it is still alive. The script must not move on.

[vexx32]

You would presumably get $_ input into the scriptblock as the error record, so you could pick what to do based on the type of $_.Exception that it receives.