Proof-of-concept for parsing "#CNAME" comments in a HOSTS file to auto-replace IP addresses

Resolve-HostsFileCName.ps1

#requires -version 3
[CmdletBinding()]
param ()

$DatabasePath = Get-CimInstance -ClassName Win32_NetworkAdapterConfiguration -Filter 'DatabasePath is not null' -Property DatabasePath |
    Select-Object -ExpandProperty DatabasePath -First 1

$DatabasePath = [Environment]::ExpandEnvironmentVariables($DatabasePath)

$HostsFilePath = Join-Path -Path $DatabasePath -ChildPath HOSTS

$Pattern = '^\s*(?<ip>\d+\.\d+\.\d+\.\d+)\s+[^#]*#CNAME\s+(?<fqdn>[^\s]+)\s*$'

(Get-Content -Path $HostsFilePath) |
    ForEach-Object {

        if ($_ -match $Pattern) {
            $IPv4Address = [System.Net.Dns]::Resolve($Matches.fqdn).AddressList |
                Where-Object { $_.AddressFamily -eq 'InterNetwork' <# ipv4 #> } |
                Select-Object -First 1

            $_ -replace ('^\s*' + [Regex]::Escape($Matches.ip)), $IPv4Address.ToString()
        } else {
            $_
        }
    } | Set-Content -Path $HostsFilePath -Encoding ASCII