PowerShell: the automatic variable $psBoundParameters

The type of $psBoundParameters is System.Management.Automation.PSBoundParametersDictionary. This type derives from from System.Collections.Generic.Dictionary<String, Object>. This dictionary's keys are the names of the passed parameters, its values the objects to which the respective parameters were bound.

Using ContainsKey('paramName') to check if a parameter was passed

$psBoundParameters.ContainsKey('paramName') evaluaters to $True if the parameter paramName was passed and $False otherwise:

function F {
   param (
      [int   ] $num,
      [string] $txt,
      [switch] $yes
   )


   if ($psBoundParameters.ContainsKey('num')) {
      "parameter num was passed and is $num"
   }
   if ($psBoundParameters.ContainsKey('txt')) {
      "parameter txt was passed and is $txt"
   }
   if ($psBoundParameters.ContainsKey('yes')) {
      "parameter yes was passed and is $yes"
   }

}


F -txt 'hello world'
#
#  parameter txt was passed and is hello world


F -num 42 -yes:$false
#
#  parameter num was passed and is 42
#  parameter yes was passed and is False

Github repository about-PowerShell, path: /language/variable/automatic/psBoundParameters/ContainsKey.ps1

Iterating over psBoundParameters

The following simple example tries to demonstrate other features of $psBoundParameters such as iterating over the parameter names:

set-strictMode -version 2

function F (
   $param_1  = 'one'  ,
   $param_2  = 'two'  ,
   $param_3  = 'three',
   $param_4  = 'four' ,
   $param_5  = 'five'
) {

  write-host "You called F"
  write-host "  The following arguments were set when F was invoked"
  foreach ($passedArgument in $psBoundParameters.Keys) {
     write-host "    $passedArgument = $($psBoundParameters[$passedArgument])"
  }

  write-host "  Of these arguments, the following were passed positionally"
  foreach ($passedPositionally in $psBoundParameters.BoundPositionally) {
     write-host "    $passedPositionally"
  }

  write-host

}


F 'foo' 'bar' 'baz'
#
#  You called F
#    The following arguments were set when F was invoked
#      param_1 = foo
#      param_2 = bar
#      param_3 = baz
#    Of these arguments, the following were passed positionally
#      param_1
#      param_2
#      param_3
#


F 'one' 'TWO' 'xyz'
#
#  You called F
#    The following arguments were set when F was invoked
#      param_1 = one
#      param_2 = TWO
#      param_3 = xyz
#    Of these arguments, the following were passed positionally
#      param_1
#      param_2
#      param_3

F -param_3 'one' -param_4 'two' -param_1 'three'
#
#  You called F
#    The following arguments were set when F was invoked
#      param_3 = one
#      param_4 = two
#      param_1 = three
#    Of these arguments, the following were passed positionally

Github repository about-PowerShell, path: /language/variable/automatic/psBoundParameters/simple.ps1

PowerShell: the automatic variable $psBoundParameters

Using ContainsKey('paramName') to check if a parameter was passed

Iterating over psBoundParameters

See also