PowerShell function parameters support a ValidateScript attribute where you can assign PowerShell code. The code is invoked when the parameter receives a value from a user, and can return $true or $false. If the code returns $false, the argument is rejected.
Here is a sample that accepts file names only if the file exists in the Windows folder:
function Get-File { param ( [Parameter(Mandatory)] [ValidateScript({ Test-Path -Path "$env:windir\$_" })] [string] $File ) "$File exists in your Windows folder." }
And here is a result:
PS C:\> Get-File -File explorer.exe explorer.exe exists in your Windows folder. PS C:\> Get-File -File something.exe Get-File : Cannot validate argument on parameter 'File'. The " Test-Path -Path "$env:windir\$_" " validation script for the argument with value "something.exe" did not return a result of True. Determine why the validation script failed, and then try the command again. At line:1 char:16 + Get-File -File something.exe + ~~~~~~~~~~~~~ + CategoryInfo : InvalidData: (:) [Get-File], ParameterBindingValidationException + FullyQualifiedErrorId : ParameterArgumentValidationError,Get-File PS C:\> Get-File -File memory.dmp memory.dmp exists in your Windows folder.
