dealing with subdomain and domain

I have a script that I use to check if a domain has dns records A,MX,SPF and DMARC.

I recently ran into a problem were if I sent the script this example test.domain.com. The function will test that as is.

I really want the script to only test the domain.com portion unless told otherwise with a switch. (I know how to build a switch)

The problem is I don’t know how to test for if a flat domain was entered versus a domain that has a subdomain like my example above. I would like to get a result of just flat domain.

ideas?

here is my function

param (
    [parameter(Mandatory = $true,
        HelpMessage = "Enter the domain name or a email address.")][string]$Domain
)

If ($Domain -notlike '*.*') {
    Write-Warning "Domain not valid please input full domain. Example Facebook.com or an email address."
    Return $null
}

Try {
    $TestDomain = ([Net.Mail.MailAddress]$Domain).Host
}
Catch {
    $TestDomain = $Domain
}

If ($TestDomain -like '@*') {
    $TestDomain = $TestDomain.Replace('@', '')
}

Return [PSCustomObject]@{
    A     = If (Resolve-DnsName -Name $TestDomain -Type 'A' -Server '8.8.8.8' -DnsOnly -ErrorAction SilentlyContinue | Where-Object { $_.type -eq 'a' } ) { $true } Else { $false }
    MX    = If (Resolve-DnsName -Name $TestDomain -Type 'MX' -Server '8.8.8.8' -DnsOnly -ErrorAction SilentlyContinue | Where-Object { $_.type -eq 'mx' } ) { $true } Else { $false }
    SPF   = If (Resolve-DnsName -Name $TestDomain -Type 'TXT'-Server '8.8.8.8' -DnsOnly -ErrorAction SilentlyContinue | where-object { $_.strings -match "v=spf1" } ) { $true } Else { $false }
    DMARC = if (Resolve-DnsName -Name "_dmarc.$($TestDomain)" -Type 'TXT' -Server '8.8.8.8' -DnsOnly -ErrorAction SilentlyContinue | Where-Object { $_.type -eq 'txt' } ) { $true } Else { $false }
}

>Solution :

I don’t know exactly what you are trying to do. I have a general idea. In order to check for a subdomain I would just use a regular expression to check for one or more ‘.’. This could be accomplished like so:

if($Domain -match '.*\..*\..*') {#Subdomain}

Here is a more detailed example using your current code and how you could apply it:

param (
    [parameter(Mandatory = $true,
        HelpMessage = "Enter the domain name or a email address.")][string]$Domain
)

#two or more "." -subdomain
If($Domain -match '.*\..*\..*')
{
     #example: photos.google.com   
     #1). if you want to take off the sub domain off of the $domain variable:
     $Domain = $Domain.Substring($Domain.IndexOf('.') +1)
     #2). or exit out 
     Write-Warning "Domain entered is a subdomain... Exiting"
     return $null
     #3). or use the "subdomain" a different way than a "root" domain
     
}
#match one ore more "." -root
elseif ($Domain -match '.*\..*')
{
    #example: google.com
    #1). Execute what you want to do with Domain here --- if doing something seperate above ... using option 2 / 3 from above condition
    #2). no need to execute anything here if you are using option 1 from above
    
}
#invalid
else
{
    Write-Warning "Domain not valid please input full domain. Example Facebook.com or an email address."
    Return $null
}


#work with the $Domain variable ... Option 1 / 2 on the first condition.

In the example above you could put your Try{} Catch{} block in the appropriate condition or after the conditions. It is really up to you how you want to handle it.