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Parameter Binding with Advanced Functions

Answered Parameter Binding with Advanced Functions

  • Friday, January 18, 2013 3:15 PM
     
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    I have a function that I want to perform 3 different tasks.  Each task is exclusive such that none of the three should be allowed to run in conjunction with the others.  Here are the tasks:

    1. Create a key
    2. Read a specific key from a text file
    3. Read the first key from a text file (default behavior) - this should run when no arguments are present.

    Here's a code snippet that I've written:

    Param 
(
	[CmdletBinding(DefaultParameterSetName="Fake")]
	[Parameter(
		ParameterSetName="ReadKey"
	)]
	[ValidateScript({$_ -ge -1})]
	[int] $ReadKey,
	[Parameter(
		ParameterSetName="CreateKey"
	)]
	[ValidateScript({$_ -gt 14})]
	[int] $CreateKey
)

if ($CreateKey)
{
	# Algorthm to create keys
	# Creates a key of length $CreateKey
}
elseif ($ReadKey)
{
	# Gets a specific key
	$keyList = Get-Content keys.txt
	$keyList[$ReadKey]
}
else
{
	# Gets the first key
	$keyList = Get-Content keys.txt
	$keyList[0]
}
    NOTE: The Fake default parameter set name is an idea that came from: http://blogs.msdn.com/b/mediaandmicrocode/archive/2009/04/10/microcode-powershell-scripting-trick-fun-with-parameter-binding-the-fake-parameter-set-trick.aspx  It did not fix the problem (obviously).  Using the real parameter set names likewise did not fix the problem.

    Problem: PowerShell keeps complaining that the parameter sets are ambiguous.  I certainly understand why, but I don't know how to get the desired behavior.  Ideas?

    I feel like there's something obvious that I'm overlooking...

    I'm the most humble person you've ever met.


    • Edited by James Keeler Friday, January 18, 2013 3:18 PM Correct title
    •  
     

All Replies

  • Friday, January 18, 2013 3:40 PM
     
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    Here is the way I want it to work from the command line:

    .\getKey.ps1
Returns the first key in keys.txt

.\getKey.ps1 -ReadKey 5
Returns the sixth key in keys.txt

.\getKey.ps1 -CreateKey 25
Creates a new key that is 25 characters long and adds it to keys.txt

    As you can see, it makes no sense to allow someone to type .\getKey.ps1 -ReadKey 5 -CreateKey 25.  It also makes complete sense that the default action would be to return the first key from the file.

    I'm the most humble person you've ever met.

     
  • Friday, January 18, 2013 3:59 PM
     
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    I solved it.  The following code performs as desired:

    Param 
(
	[ValidateScript({$_ -ge -1})]
	[int] $ReadKey,
	[ValidateScript({$_ -gt 14})]
	[int] $CreateKey
)

if ($PSBoundParameters.ContainsKey('CreateKey') -and $PSBoundParameters.ContainsKey('ReadKey'))
{
	throw "Invalid parameters."
}
elseif ($PSBoundParameters.ContainsKey('CreateKey'))
{
	# Algorthm to create keys
	# Creates a key of length $CreateKey
}
elseif ($PSBoundParameters.ContainsKey('ReadKey'))
{
	# Gets a specific key
	$keyList = Get-Content keys.txt
	$keyList[$ReadKey]
}
else
{
	# Gets the first key
	$keyList = Get-Content keys.txt
	$keyList[0]
}

    I'm the most humble person you've ever met.

    • Marked As Answer by James Keeler Friday, January 18, 2013 4:00 PM
    •  
     
  • Friday, January 18, 2013 5:55 PM
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    1

    I think that's a good solution and it's actually what I was going to suggest - dispense with creating parameter sets and just check which parameters are actually specified.

    Bill