Advanced Windows PowerShell Scripting Video Training

Advanced Windows PowerShell Scripting Video Training
Advanced Windows PowerShell Scripting Video Training

Tuesday, August 30, 2016

How to use Write-Information

It is always fun to write on a topic that people are passionate about.  Yes, we will be talking about Write-Host in this post.  I know, you either love it or you hate it.

PowerShell uses different “streams” of information.  Here is a quick visual.

Stream |  Definition             | Cmdlet
1      |  Success output         | Write-Output      
2      |  Errors                 | Write-Error       
3      |  Warning messages       | Write-Warning     
4      |  Verbose output         | Write-Verbose     
5      |  Debug messages         | Write-Debug       
6      |  Informational messages | Write-Information 
NA     |  User Experience        | Write-Host         

The above is a little display that I use in class.  Yes, it is created with Write-HostWrite-Host is OK to use if you need to create a user interface of some type.  PowerShell was designed to use the pipeline.  This is stream 1.  Notice that there is no stream for Write-HostWrite-Host sends information directly to the monitor.  There is a stream for Write-Information.

Write-Information became available with PowerShell 5.  Why do we have another cmdlet to put information on the screen? Well, first of all, the end user cannot stop Write-Host from working.  Take a look at this.

PS C:\>     $InformationPreference
SilentlyContinue

The information stream is controlled by a global variable called $InformationPreferenceWrite-Host has no such global variable controlling it.  By default, your information messages are not displayed.

PS C:\> Write-Information -MessageData "Nothing will display"

PS C:\> 

However, you can override this in code.
PS C:\> Write-Information -MessageData "Something will display" -InformationAction Continue
Something will display

The –InformationAction parameter is one of the common parameters.  That means the user running the code can ask for your information messages if they want to see them.  You can also redirect the output of your information stream to another stream if it is appropriate.  You cannot do that with Write-Host because it sends information directory to the screen.  Below is a comparison of the two commands.

Feature
Write-Host
Write-Information
Writes directly to the screen
Yes
No
Can display colors
Yes
No
Can be suppressed by the user
No
Yes
Can be redirected to another stream
No
Yes
Can have TAGs in the metadata
No
Yes
Can be saved in a variable
No
Yes


I understand the draw that Write-Host has with its ability to display colors.  If you are creating a script that requires user interaction, go for it.  If you want code that works well with the pipeline and does not display information on the screen (Which can slow processing times) then consider making the switch to Write-Information.

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