Redirect Write-Host statements to a file

Question

I have a PowerShell script that I am debugging and would like to redirect all Write-Host statements to a file. Is there an easy way to do that?

Answer 1

I just added Start-Transcript at the top of the script and Stop-Transcript at the bottom.

The output file was intended to be named <folder where script resides>-<datestamp>.rtf, but for some reason the trace file was being put where I did not expect it — the desktop!

Answer 2

If you have just a few Write-Host statements, you can use the "6>>" redirector operator to a file:

Write-Host "Your message." 6>> file_path_or_file_name

This is the "Example 5: Suppress output from Write-Host" provided by Microsoft, modified accordingly to about_Operators.

Answer 3

This worked for me in my first PowerShell script that I wrote few days back:

function logMsg($msg)
{
    Write-Output $msg
    Write-Host   $msg
}

Usage in a script:

logMsg("My error message")
logMsg("My info message")

PowerShell script execution call:

ps> .\myFirstScript.ps1 >> testOutputFile.txt

It's not exactly answer to this question, but it might help someone trying to achieve both logging to the console and output to some log file, doing what I reached here :)

Answer 4

You can run your script in a secondary PowerShell shell and capture the output like this:

powershell -File 'Your-Script.ps1' > output.log

That worked for me.

Answer 5

You can create a proxy function for Write-Host which sends objects to the standard output stream instead of merely printing them. I wrote the below cmdlet for just this purpose. It will create a proxy on the fly which lasts only for the duration of the current pipeline.

A full writeup is on my blog here, but I've included the code below. Use the -Quiet switch to suppress the console write.

Usage:

PS> .\SomeScriptWithWriteHost.ps1 | Select-WriteHost | out-file .\data.log  # Pipeline usage
PS> Select-WriteHost { .\SomeScriptWithWriteHost.ps1 } | out-file .\data.log  # Scriptblock usage (safer)

function Select-WriteHost
{
   [CmdletBinding(DefaultParameterSetName = 'FromPipeline')]
   param(
     [Parameter(ValueFromPipeline = $true, ParameterSetName = 'FromPipeline')]
     [object] $InputObject,

     [Parameter(Mandatory = $true, ParameterSetName = 'FromScriptblock', Position = 0)]
     [ScriptBlock] $ScriptBlock,

     [switch] $Quiet
   )

   begin
   {
     function Cleanup
     {
       # Clear out our proxy version of write-host
       remove-item function:\write-host -ea 0
     }

     function ReplaceWriteHost([switch] $Quiet, [string] $Scope)
     {
         # Create a proxy for write-host
         $metaData = New-Object System.Management.Automation.CommandMetaData (Get-Command 'Microsoft.PowerShell.Utility\Write-Host')
         $proxy = [System.Management.Automation.ProxyCommand]::create($metaData)

         # Change its behavior
         $content = if($quiet)
                    {
                       # In quiet mode, whack the entire function body,
                       # simply pass input directly to the pipeline
                       $proxy -replace '(?s)\bbegin\b.+', '$Object'
                    }
                    else
                    {
                       # In noisy mode, pass input to the pipeline, but allow
                       # real Write-Host to process as well
                       $proxy -replace '(\$steppablePipeline\.Process)', '$Object; $1'
                    }

         # Load our version into the specified scope
         Invoke-Expression "function ${scope}:Write-Host { $content }"
     }

     Cleanup

     # If we are running at the end of a pipeline, we need
     #    to immediately inject our version into global
     #    scope, so that everybody else in the pipeline
     #    uses it. This works great, but it is dangerous
     #    if we don't clean up properly.
     if($pscmdlet.ParameterSetName -eq 'FromPipeline')
     {
        ReplaceWriteHost -Quiet:$quiet -Scope 'global'
     }
   }

   process
   {
      # If a scriptblock was passed to us, then we can declare
      #   our version as local scope and let the runtime take
      #   it out of scope for us. It is much safer, but it
      #   won't work in the pipeline scenario.
      #
      #   The scriptblock will inherit our version automatically
      #   as it's in a child scope.
      if($pscmdlet.ParameterSetName -eq 'FromScriptBlock')
      {
        . ReplaceWriteHost -Quiet:$quiet -Scope 'local'
        & $scriptblock
      }
      else
      {
         # In a pipeline scenario, just pass input along
         $InputObject
      }
   }

   end
   {
      Cleanup
   }
}

Answer 6

Try using Write-Output instead of Write-Host.

The output goes down the pipeline, but if this is the end of the pipe, it goes to the console.

> Write-Output "test"
test
> Write-Output "test" > foo.txt
> Get-Content foo.txt
test