Passing no parameters

This was interesting question on the forum – user wants to retrieve something by name or id and if neither are given then return all objects.  This is similar to

Get-Process powershell
Get-Process -Id 1568
Get-Process

In the first two we filter on a name or id – in the last one we get everything

This is what I arrived at using processes as an example

function test-proc{             
[CmdletBinding(DefaultParameterSetName="XXXXX")]             
param (             
[parameter(Position=0,            
   ParameterSetName="ByName",            
   ValueFromPipeline=$true,             
   ValueFromPipelineByPropertyName=$true)]            
   [ValidateNotNullOrEmpty()]            
   [string]$name,            
               
   [parameter(Position=0,            
   ParameterSetName="ById",            
   ValueFromPipeline=$true,             
   ValueFromPipelineByPropertyName=$true)]            
   [ValidateNotNullOrEmpty()]            
   [int]$id              
)             
BEGIN{}#begin             
PROCESS{            
            
switch ($psCmdlet.ParameterSetName) {            
 "ByName"  {Get-Process -Name $name }            
 "ById"  {Get-Process -Id $id }            
 "XXXXX" {Get-Process }            
}            
}#process             
END{}#end            
}            
            
##

The trick is to define a default parameter set with no parameters – then when you don’t use any parameters it kicks in at the switch statement and your code can run as required

Be interested if this gets broken in any scenarios as it seems to simple to be correct – but it works