2014 Winter PowerShell Scripting Games Wrap Up #4

Dr Scripto

Summary: Microsoft Scripting Guy, Ed Wilson, continues his Scripting Games 2014 wrap up with a discussion of error and verbose message streams.

Microsoft Scripting Guy, Ed Wilson, is here. Things are starting to settle down here in the scripting household. Windows PowerShell Saturday #007 was a rousing success in Charlotte, North Carolina. Valentine’s Day was cool and a special treat for the Scripting Wife and I, and the 2014 Winter Scripting Games have concluded. So what’s to do? Well, today I am sipping a nice cup of Charleston Breakfast tea. I added peppermint, spearmint, honey, fresh lemon, and a cinnamon stick to the mixture. It is quite refreshing. Charleston Breakfast tea is one of the teas that is grown at the Charleston Tea Plantation. It has a nice robust flavor when steeped for four minutes in 208 degree water.

     Note  This is the fourth in a series of blog posts in which I talk about things I noticed whilst grading submissions for the
     2014 Winter Scripting Games. In case you missed the previous episodes:

• 2014 Winter PowerShell Scripting Games Wrap Up #1
  Talked about best practices for using aliases and for formatting of Windows PowerShell scripts.
• 2014 Winter PowerShell Scripting Games Wrap Up #2
  Talked about the need for and the use of structured error handling.
• 2014 Winter PowerShell Scripting Games Wrap Up #3
  Talked about using standard Windows folders from within Windows PowerShell scripts.

In today’s post, I’ll talk about using the Write-Verbose and Write-Error streams in Windows PowerShell scripts.

Alternative output message streams

One of the things I saw while grading scripts for the 2014 Winter Scripting Games was people creating their own alternate message streams. For example, they might do something like the following:

If($verbose) {Write-Host "This is verbose output"}

ELSE {Write-Host "This is normal output"}

Although this sort of thing might actually work (at least to an extent), it is not optimal. In fact, it causes a lot of extra work. This is because Windows PowerShell already has several message streams including:

• Normal output
• Errors
• Warnings
• Verbose output
• Debug messages

Whether these messages display anything is due to the configuration of one of the following Preference variables:

• DebugPreference
• ErrorActionPreference
• VerbosePreference
• WarningPreference

The neat thing is that I implement my script in the proper Windows PowerShell fashion, then I can capture these alternate message streams in a text file via the redirection operators introduced in Windows PowerShell 3.0. The following table lists the redirection operators.

Note  The 2>, 2>>, and 2&1 operators existed in Windows PowerShell 1.0.

An example of how to use the alternate message streams is shown here:

$desktopPath = [System.Environment]::GetFolderPath("Desktop")

Function Out-VerboseStream

{

 BEGIN { $oldVerbosePreference = $VerbosePreference }

 PROCESS {

 $VerbosePreference = "Continue"

  Write-Verbose "This is verbose output"

  "This is regular output" }

END {$VerbosePreference = $oldVerbosePreference }

}

The key features are to set the preference variable to “Continue” to permit it to output. As a best practice, you should set it back when you are finished. As shown in the following image, I first run the function, and the verbose stream and the regular stream appear in the output pane.

I now use the redirection operator to redirect the verbose stream output to a text file:

Now when I use the redirection operator to redirect the verbose stream, it goes in a text file.

The following table illustrates the different type of redirection characters that are used to represent the message streams.

That is all there is to using different output streams. 2014 Winter PowerShell Scripting Games Wrap-Up Week continues tomorrow when I will talk about using the Switch statement.

I invite you to follow me on Twitter and Facebook. If you have any questions, send email to me at scripter@microsoft.com, or post your questions on the Official Scripting Guys Forum. See you tomorrow. Until then, peace.

Ed Wilson, Microsoft Scripting Guy 

Dr Scripto

Scripter, PowerShell, vbScript, BAT, CMD