Create a mandatory parameter if another parameter is chosen

Is it possible to define a parameter that is only mandatory if another parameter is set?

fast example:

param (
  [parameter(mandatory=$true)][string][ValidateSet("Option1","Option2")]$Mode,
  [parameter][string]$Option
  )

Basically let’s say I’d like to set $Option to mandatory but only if $mode=“Option2”. Obviously I can do this easily enough in the script outside of the param block, but I figured I’d ask if there was a more elegant way?

Nope. You’ll have to add that validation logic inside the function somewhere. (Usually in the Begin block, but might need to be in Process if either of those parameters can accept pipeline input.)

Well, technically you can use dynamic parameters, but that’s even less friendly. :slight_smile:

You can do what you’re asking - that’s what parameter sets are for - if you approach the logic slightly differently. Instead of an “Option” switch…

Set A:
-Option1

Set B:
-Option2 -Mode

Where -Mode is always mandatory, but only gets engaged if run with -Option2. This is more the pattern you see Microsoft use in the native cmdlets.