Richard Siddaway's Blog

Many scripting languages require you explicitly write out to screen – VBScript was an example.

This leads to PowerShell that looks like this

Get-Service |
foreach {
  Write-Host $_.Name, $_.Status
}

This is bad on so many levels.

Firstly you are doing too much work. Secondly you are emitting text not objects. Thirdly you are doing too much work.

Get-Service |
Format-Table Name, Status –AutoSize

gives a much better result and if you are working at the prompt can be aliased to

gsv | ft Name, Status –a

The last act of the pipeline is to pass the data to Out-Default which performs the screen writing.  Write-Host also passes data to Out-Default which effectively terminates the pipeline.

You should always format the data for display as far into the processing as you possibly can. Once you have called a format cmdlet or Write-Host you have terminated the pipeline.

The best you will get is the text representation that would have been displayed on screen. The worst is garbage output.

So if you want to create a HTML report then

Get-Service |
Select Name, Status |
ConvertTo-Html |
Out-File test.htm

Invoke-Item test.htm

Stick with objects and let the pipeline do the work

Many forum questions revolve around that question.  In some cases the answer is that its not possible.

It might not be possible because PowerShell itself can’t do something BUT it is much more likely that there just isn’t away to do that particular action programmatically (through a script).

Its always a good idea to work out how you are going to do something before you try to figure out how you will get PowerShell to do it for you

A question on the forum asked about creating a function that accepts pipeline input OR has a path parameter.  Means it can be used like this

myfunction -Path C:\scripts\Test\proc.csv

or

(Get-Content C:\scripts\Test\files.txt) | myfunction

First create a csv file

Get-Process | Export-Csv proc.csv –NoTypeInformation

and test its contents

Import-Csv proc.csv

The full path to the csv file is:-  C:\scripts\Test\proc.csv

The function is like this

function myfunction{             
[CmdletBinding()]             
param (             
[parameter(ValueFromPipeline=$true,             
   ValueFromPipelineByPropertyName=$true)]            
   [string]$Path            
)             
PROCESS{            
 if (-not (Test-Path -Path $path)){            
   Throw "Path NOT found $path"            
 }            
            
 Import-Csv -Path $path            
            
}#process             
            
}

Use [CmdletBinding()] to get the debug and verbose parameters

Use ValueFromPipeline and ValueFromPipelineByPropertyName attributes [parameter()]

This covers generic input and if we have a csv with path as a column.

if you are accepting pipeline input you need to use a PROCESS block

Then the path is tested and rejected if not valid. Finally import-csv is used to read the file