Powershell command did not include error in output file

Question

I have the code below, to be used in Powershell; it performed well, except that I need the output file to also include the error messages whenever the IPs did not resolve to names.

Get-Content inputfile.txt | 
    foreach-object { [System.Net.Dns]::GetHostEntry($_)  } | 
    out-file -filepath outputfile.txt

At the moment, I'm able to see the red error messages displayed on Powershell window. But I want these to appear in the output file along with the results for each item listed in the input file.

Thanks in advance!

Answer 1

Since .GetHostEntry(..) doesn't give you a clear hint as to which IP failed to be resolved it's better if you create an object that associates the IP Address you're trying to resolve with the method call . This also allows you to have a better export type, instead of plain .txt file, you can export your objects as .csv with Export-Csv .

Below example uses .GetHostEntryAsync(..) which allow us to query multiple hosts in parallel!

using namespace System.Collections.Generic
using namespace System.Collections.Specialized

(Get-Content inputfile.txt).ForEach{
    begin { $tasks = [List[OrderedDictionary]]::new() }
    process {
        $tasks.Add([ordered]@{
            Input    = $_
            Hostname = [System.Net.Dns]::GetHostEntryAsync($_)
        })
    }
    end {
        do {
            $id = [System.Threading.Tasks.Task]::WaitAny($tasks.Hostname, 200)
            if($id -eq -1) { continue }
            $thisTask = $tasks[$id]
            $thisTask['Hostname'] = try {
                $thisTask.Hostname.GetAwaiter().GetResult().HostName
            }
            catch { $_.Exception.Message }
            $tasks.RemoveAt($id)
            [pscustomobject] $thisTask
        } while($tasks)
    }
} | Export-Csv outputfile.csv -NoTypeInformation