Handling pipeline and parameter input in a Powershell function

Question

I'm confused about something I saw in the book Learn PowerShell in a Month of lunches. In chapter 21 when the author discusses functions that accept input via parameter binding or the pipeline he gives two patterns.

The first as follows

function someworkerfunction {
# do some work
}
function Get-SomeWork {
   param ([string[]]$computername)
   BEGIN {
      $usedParameter = $False
      if($PSBoundParameters.ContainsKey('computername')) {
         $usedParameter = $True
      }   
   }
   PROCESS {
      if($usedParameter) {
         foreach($computer in $computername) {
            someworkerfunction -computername $comptuer
         }
      } else {
         someworkerfunction -comptuername $_
      }
   }

   END {}
}

The second like this

function someworkerfunction {
# do stuff
}
function Get-Work {
   [CmdletBinding()]
   param(
      [Parameter(Mandatory=$True,
      ValueFromPipelineByPropertyName=$True)]
      [Alias('host')]
      [string[]]$computername
   )
   BEGIN {}
   PROCESS {
      foreach($computer in $computername) {
         someworkerfunction -comptuername $computer
      }
   }
   END {}
}

I know the second sample is a standard Powershell 2.0 Advanced function. My question is with Powershell 2.0 support for the cmdletbinding directive would you ever want to use the first pattern. Is that just a legacy from Powershell 1.0? Basically is there ever a time when using Powershell 2.0 that I would want to mess around with the first pattern, when the second pattern is so much cleaner.

Any insight would be appreciated.

Thank you.

Answer 1

If you want to process pipeline input in your function but don't want to add all the parameter attributes or want backwards compatibility go with the cmdletbindingless way.

If you want to use the additional features of PowerShell script cmdlets like the parameter attributes, parameter sets etc... then go with the second one.

Answer 2

If anyone wishes for a very, very simple explanation of how to read from piped input see

How do you write a powershell function that reads from piped input?

Had this ^ existed when I had this question, I would have saved a lot of time because this thread is quite complicated and doesn't actually explain how to handle pipelined input into a function.