Author Posts

September 21, 2014 at 5:12 pm

I thought if you use a switch parameter you don't have to specify whether the parameter is true or false, but rather just using the parameter itself tells PowerShell that it is true.

For instance, if I do something like in the following example, PowerShell responds with an error wanting the parameter to be specified explicitly as $false:

Function Do-Something
{
param
(
[switch]param1
)
}

Do-Something -param1

However, if I do this, it works fine:

Function Do-Something
{
param
(
[switch]param1
)
}

Do-Something -param1 $true

So we have to state that the parameter be true if we want it to be used? I thought just stating the parameter tells PowerShell that it is true?

Any help it would be appreciated, as always.

Thanks everyone

September 21, 2014 at 5:13 pm

Sorry, not explicitly as $false, but $true. That was a typo

September 21, 2014 at 5:51 pm

For the most part, you're correct. Switch parameters, in their general usage, are $false if you don't specify them on the command line, and are $true if you do specify them on the command line. They don't take any arguments (again, in the general usage case):

function MyFunction([switch] $MySwitch) { }

MyFunction # $MySwitch is $false

MyFunction -MySwitch # $MySwitch is $true

However, sometimes you do need to be able to pass in a specific value for the switch parameter, either because you're passing it on from one function to another (such as in a proxy function), or because you need to deliberately set a switch to $false (which is rare, but you'll sometimes see this with -Confirm:$false . In this case, setting Confirm explicitly to false causes it to override the behavior of the $ConfirmPreference variable, which would otherwise be used.) When you do need to pass an argument to a switch parameter, you need place a colon between the parameter and its argument, like so:

MyFunction -MySwitch:$false

If you're using splatting with a hashtable, you can just assign a value of $true or $false to that key of the hashtable, and PowerShell knows what to do with it:

$params = @{ MySwitch = $true }

MyFunction @params

September 21, 2014 at 7:34 pm

firstly, neither of those examples work for me from just copy/pasting as you've neglected the '$' in the parameter declaration so there is a general error and the function cannot be defined. The function should be like:

Function Do-Something
{
param
(
[switch]$param1
)
}

Do-Something -param1

Can you provide the exact error message you're getting?

September 21, 2014 at 8:07 pm

Thanks Dave, but when I use the switch parameter I get the following error:

[b]Missing an argument for parameter Param1.[/b]

Peter,

The code I used was just pseudo code, it was not my actual code.

My actual code looks something like this:

{Function Do-Something
{
    [cmdletbinding()] 
     
    Param  
    (                 
         [Parameter(Mandatory=$false,  
         [switch[]]$Param1,

         [Parameter(Mandatory=$false, 
         [switch[]]$Param2,

         [Parameter(Mandatory=$false, 
         [switch[]]$Param3
    )   

Begin {}

End {}

Please note, this also is not my identical code, but this is as close to it as possible.

Thanks

September 21, 2014 at 8:20 pm

Okay, I found the issue. I used "[switch[]]" and after I removed the inner "[]" and just used "[switch]", it worked like intended.

Can someone explain to me why the other way did not work? What are the inner "[]" used for?

Thanks

September 22, 2014 at 2:57 am

[switch[]] would indicate an array of SwitchParameter objects, which doesn't really make any sense (though I suppose it's technically legal.)

September 22, 2014 at 11:46 am

oh i see

Thanks again, Dave