ValidatePattern in PowerShell: While value doesn't match - powershell

Question

I want to perform a pattern validation of a string value I'm entering and then only continue with the script if it matches but feel like I'm missing something here:
Function Test-ValidatePattern {
[CmdletBinding()]
param (
[Parameter(Mandatory)]
[ValidatePattern(".co.uk|.com")]
[System.String]$DomainName
)
$DomainValid = "1"
Write-Output "$DomainName is a valid domain name format"
}
#Sets forwarding email address, checks what it's set to and outputs this to logfile.
If ($EmailForwarding) {
$ForwardDomain = Read-Host "What domain do you want to forward to? e.g. contoso.com`n"
Test-ValidatePattern -DomainName $ForwardDomain
While (!($DomainValid -eq "1")) {
Write-Host "$ForwardDomain isn't a valid domain. Try again"
$ForwardDomain = Read-Host "What domain do you want to forward to? e.g. contoso.com`n"
}
}
It returns an error as expected when entering a string that doesn't have a .co.uk or .com extension and no error when entering one that does but rather than presenting the message that the domain name is valid it loops back to the while block messages instead of continuing on with the rest of the script.
I've tried -eq, -notmatch, -notlike but still not working as intended.
Any ideas?

Answer 1

I don't understand why you think you need to write a validation script when that is the purpose of the ValidatePattern attribute. Here is an example function:
function sample {
param(
[Parameter(Mandatory=$true)]
[ValidatePattern('(\.co\.uk|\.com)$')]
[String] $DomainName
)
"Your domain name is $DomainName"
}
If you run
sample foo.bar
PowerShell will throw a ParameterBindingValidationException exception because the string you passed as the $DomainName parameter doesn't match the pattern. However, if you run
sample foo.com
You will see the expected output:
Your domain name is foo.com

Answer 2

You're not setting $DomainValid to any value. The scope of the function clears out $DomainValid when it finishes. You'll need to return a value from the Test-ValidatePattern function. For Example:
Function Test-ValidatePattern {
[CmdletBinding()]
param (
[Parameter(Mandatory)]
[ValidatePattern(".co.uk|.com")]
[System.String]$DomainName
)
#$DomainValid = "1"
Write-Output "$DomainName is a valid domain name format"
return 1
}
#Sets forwarding email address, checks what it's set to and outputs this to logfile.
If ($EmailForwarding) {
$ForwardDomain = Read-Host "What domain do you want to forward to? e.g. contoso.com`n"
$DomainValid = Test-ValidatePattern -DomainName $ForwardDomain
While (!($DomainValid -eq "1")) {
Write-Host "$ForwardDomain isn't a valid domain. Try again"
$ForwardDomain = Read-Host "What domain do you want to forward to? e.g. contoso.com`n"
}
}

Answer 3

I feel I've missed off a few things when explaining what I was after. I simply wanted to make sure the input had a dot present so single words couldn't be entered e.g. "foo.bar" is allowed but "foo" isn't. If not present then the user should be prompted again. Nothing too strict and doesn't stop invalid entries but more so to catch a lazy input.
After tinkering around a bit more the below appears to do what I require.
If ($EmailForwarding) {
$ForwardDomain = Read-Host "What domain do you want to forward to? e.g. contoso.com`n"
While (!($ForwardDomain -like "*.*"))
{Write-Host "$ForwardDomain isn't a valid domain. Try again"
$ForwardDomain = Read-Host "What domain do you want to forward to? e.g. contoso.com`n"}}
"rest of script"