Private/GetDomainName.ps1

function GetDomainName {
    [CmdletBinding()]
    Param()

    if (!$PSVersionTable.Platform -or $PSVersionTable.Platform -eq "Win32NT") {
        $Domain = $(Get-CimInstance Win32_ComputerSystem).Domain
    }
    if ($PSVersionTable.Platform -eq "Unix") {
        $Domain = domainname
        if (!$Domain -or $Domain -eq "(none)") {
            $ThisHostNamePrep = hostname
            if ($ThisHostNamePrep -match "\.") {
                $HostNameArray = $ThisHostNamePrep -split "\."
                $ThisHostName = $HostNameArray[0]
                $Domain = $HostNameArray[1..$HostNameArray.Count] -join '.'
            }
        }
            
        if (!$Domain) {
            $EtcHostsContent = Get-Content "/etc/hosts"
            $EtcHostsContentsArray = $(foreach ($HostLine in $EtcHostsContent) {
                $HostLine -split "[\s]" | foreach {$_.Trim()}
            }) | Where-Object {![System.String]::IsNullOrWhiteSpace($_)}
            $PotentialStringsWithDomainName = $EtcHostsContentsArray | Where-Object {
                $_ -notmatch "localhost" -and
                $_ -notmatch "localdomain" -and
                $_ -match "\." -and
                $_ -match "[a-zA-Z]"
            } | Sort-Object | Get-Unique

            if ($PotentialStringsWithDomainName.Count -eq 0) {
                Write-Error "Unable to determine domain for $(hostname)! Please use the -DomainName parameter and try again. Halting!"
                $global:FunctionResult = "1"
                return
            }
            
            [System.Collections.ArrayList]$PotentialDomainsPrep = @()
            foreach ($Line in $PotentialStringsWithDomainName) {
                if ($Line -match "^\.") {
                    $null = $PotentialDomainsPrep.Add($Line.Substring(1,$($Line.Length-1)))
                }
                else {
                    $null = $PotentialDomainsPrep.Add($Line)
                }
            }
            [System.Collections.ArrayList]$PotentialDomains = @()
            foreach ($PotentialDomain in $PotentialDomainsPrep) {
                $RegexDomainPattern = "^([a-zA-Z0-9][a-zA-Z0-9-_]*\.)*[a-zA-Z0-9]*[a-zA-Z0-9-_]*[[a-zA-Z0-9]+$"
                if ($PotentialDomain -match $RegexDomainPattern) {
                    $FinalPotentialDomain = $PotentialDomain -replace $ThisHostName,""
                    if ($FinalPotentialDomain -match "^\.") {
                        $null = $PotentialDomains.Add($FinalPotentialDomain.Substring(1,$($FinalPotentialDomain.Length-1)))
                    }
                    else {
                        $null = $PotentialDomains.Add($FinalPotentialDomain)
                    }
                }
            }

            if ($PotentialDomains.Count -eq 1) {
                $Domain = $PotentialDomains
            }
            else {
                $Domain = $PotentialDomains[0]
            }
        }
    }

    if ($Domain) {
        $Domain
    }
    else {
        Write-Error "Unable to determine Domain Name! Halting!"
        $global:FunctionResult = "1"
        return
    }
}

# SIG # Begin signature block
# MIIM3gYJKoZIhvcNAQcCoIIMzzCCDMsCAQExCzAJBgUrDgMCGgUAMGkGCisGAQQB
# gjcCAQSgWzBZMDQGCisGAQQBgjcCAR4wJgIDAQAABBAfzDtgWUsITrck0sYpfvNR
# AgEAAgEAAgEAAgEAAgEAMCEwCQYFKw4DAhoFAAQUeqfJM3K8A6InvC/wFroQypby
# GAegggpPMIIEKTCCAxGgAwIBAgITRAAAAALGGh0rrvpIiwAAAAAAAjANBgkqhkiG
# 9w0BAQsFADBAMRMwEQYKCZImiZPyLGQBGRYDbGFiMRUwEwYKCZImiZPyLGQBGRYF
# YWxwaGExEjAQBgNVBAMTCUFscGhhREMwMTAeFw0xODExMDYxNTQ2MjhaFw0yMDEx
# MDYxNTU2MjhaMEExEzARBgoJkiaJk/IsZAEZFgNsYWIxFTATBgoJkiaJk/IsZAEZ
# FgVhbHBoYTETMBEGA1UEAxMKQWxwaGFTdWJDQTCCASIwDQYJKoZIhvcNAQEBBQAD
# ggEPADCCAQoCggEBAJ0yJxQZZ7jXPnBuOefihL0ehpBF1zoZpcM30pWneQA/kk9w
# ByX9ISyKWTABstiIu8b2g6lKUjZBM8AOcLPSjl1ZMQkh+qaSQbJFVNeNYllGpjd1
# oOYvSPtr9iPpghVkAFWw9IdOgnd/4XDd4NqlddyR4Qb0g7v3+AMYrqhQCk2VzELp
# 215LEO9sy1EMy7+B29B6P43Rp7ljA9Wc4Hnl+onviFWcIxmIhd0yGdobSxOSDgv5
# SUBfwk+DW03Y9pmJJHCU9hXFFVsPnrfBEvicGrkYx0vA+/O+jh5otex4eR+Tt7eB
# 5VhrfdHKbEkZnBwrJOVz3rURZIu3BsDFSfwNd70CAwEAAaOCARkwggEVMBAGCSsG
# AQQBgjcVAQQDAgEAMB0GA1UdDgQWBBRWBfwwFO+72Ebloy7rHmHnxX3k5DAZBgkr
# BgEEAYI3FAIEDB4KAFMAdQBiAEMAQTAOBgNVHQ8BAf8EBAMCAYYwDwYDVR0TAQH/
# BAUwAwEB/zAfBgNVHSMEGDAWgBTq79v4G/Vf91c0y+vSJBWEI/vmDTA8BgNVHR8E
# NTAzMDGgL6AthitodHRwOi8vcGtpLmFscGhhLmxhYi9jZXJ0ZGF0YS9BbHBoYURD
# MDEuY3JsMEcGCCsGAQUFBwEBBDswOTA3BggrBgEFBQcwAoYraHR0cDovL3BraS5h
# bHBoYS5sYWIvY2VydGRhdGEvQWxwaGFEQzAxLmNydDANBgkqhkiG9w0BAQsFAAOC
# AQEAoE9hHZ0Y5M5tC15cnxVNJa/ILfwRmwCxzPyOAUrdBu4jbSHF2vRsKIJAXFs4
# +mwXqXpLYSUbXF5tfB86OKs2f9L7soln3BXJHj3eEs27htf7RJK1JjPtO8rs3pdn
# h7TbDO3nyjkTcywJioScFZUTdIsQj7TBm3HIQ+/ZSdIWMHlQnYV2kW13XqUZnLhv
# PRjy1NMBG1BAxUrc4bMi1X+mVxoYb/tiB59jakd95wi7ICi2H/07dXoDpi+kAQA1
# ki1/U+cuDhuH7Q8hegt64MlmKD01rO5HODVujuIG1+M5ZkGDeLNKksPHcSJ/DBSn
# KjZca16Sn9No2kLq1q9gD8X/wzCCBh4wggUGoAMCAQICE3AAAAAHhXSIXehTWisA
# AAAAAAcwDQYJKoZIhvcNAQELBQAwQTETMBEGCgmSJomT8ixkARkWA2xhYjEVMBMG
# CgmSJomT8ixkARkWBWFscGhhMRMwEQYDVQQDEwpBbHBoYVN1YkNBMB4XDTE4MTEw
# NzAzMTQyMFoXDTE5MTEwNzAzMTQyMFowTzETMBEGCgmSJomT8ixkARkWA2xhYjEV
# MBMGCgmSJomT8ixkARkWBWFscGhhMQ4wDAYDVQQDEwVVc2VyczERMA8GA1UEAxMI
# YWxwaGFkZXYwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQCMUGwGv3p0
# prkDmSUQphU6UvIFQ57NxJFUOSmMZ7SY/nYNDy0iTN26eD0S5J8AQE8B/IGLHUno
# tKFl2AUcQ31hpaSLE1YkThR3WZ4SFUaBMUgKKLc/RQKqE0iNbAfh53N/nnGs6jyu
# 47kyuFRwWE2tZee6b5hh0dbT7YZnahLO7cLWErU4ikWWjEA98TcMK1gaNa5ThBn1
# +4bo9wuxjRKIGpkUJBP/1gq8qeSJnfNelZ34lD0EEirj7/YTzL5YkHMSXTuFMozw
# Av4lXUW/qZ1pAT9rKBalQETxBv9SuC31hU/2EiB4EYYqVFLHglFRogLd7nFZhqa/
# 2O+WdW2LsW9lAgMBAAGjggL/MIIC+zAOBgNVHQ8BAf8EBAMCB4AwHQYDVR0OBBYE
# FMy71rz8tJOXdsGvBt6SIVSKUlrkMB8GA1UdIwQYMBaAFFYF/DAU77vYRuWjLuse
# YefFfeTkMIH3BgNVHR8Ege8wgewwgemggeaggeOGgbJsZGFwOi8vL0NOPUFscGhh
# U3ViQ0EsQ049QWxwaGFTdWJDQSxDTj1DRFAsQ049UHVibGljJTIwS2V5JTIwU2Vy
# dmljZXMsQ049U2VydmljZXMsQ049Q29uZmlndXJhdGlvbixEQz1hbHBoYSxEQz1s
# YWI/Y2VydGlmaWNhdGVSZXZvY2F0aW9uTGlzdD9iYXNlP29iamVjdENsYXNzPWNS
# TERpc3RyaWJ1dGlvblBvaW50hixodHRwOi8vcGtpLmFscGhhLmxhYi9jZXJ0ZGF0
# YS9BbHBoYVN1YkNBLmNybDCB9AYIKwYBBQUHAQEEgecwgeQwgacGCCsGAQUFBzAC
# hoGabGRhcDovLy9DTj1BbHBoYVN1YkNBLENOPUFJQSxDTj1QdWJsaWMlMjBLZXkl
# MjBTZXJ2aWNlcyxDTj1TZXJ2aWNlcyxDTj1Db25maWd1cmF0aW9uLERDPWFscGhh
# LERDPWxhYj9jQUNlcnRpZmljYXRlP2Jhc2U/b2JqZWN0Q2xhc3M9Y2VydGlmaWNh
# dGlvbkF1dGhvcml0eTA4BggrBgEFBQcwAoYsaHR0cDovL3BraS5hbHBoYS5sYWIv
# Y2VydGRhdGEvQWxwaGFTdWJDQS5jcnQwPQYJKwYBBAGCNxUHBDAwLgYmKwYBBAGC
# NxUIhLycPIHG3hyBiYk0hLvpfobokGRgg9+kPoHDslgCAWQCAQIwHwYDVR0lBBgw
# FgYKKwYBBAGCNwoDDAYIKwYBBQUHAwMwKQYJKwYBBAGCNxUKBBwwGjAMBgorBgEE
# AYI3CgMMMAoGCCsGAQUFBwMDMC0GA1UdEQQmMCSgIgYKKwYBBAGCNxQCA6AUDBJh
# bHBoYWRldkBhbHBoYS5sYWIwDQYJKoZIhvcNAQELBQADggEBAIhV0GPEvq5KwIs+
# DTqLsqHcojMyJhJwrZkEim2XAJfNQFkiDrZzism7lOyXYJol6Bjz1txhos7P194+
# VyBdEZ/Q+r94hrq6SFgC2gCAReDZiy50Au/hTv958QNX/O0OFdIGBxavLqBrWbwu
# yH+RtE9E4LICSPPd0dM/5XE0xtqDMjZcl3pVkqgHpv3O3zgtsTW+FWr4b9lq3rCO
# HxsBGU1w7Eh0LLK8MLqioecr/4B1rPTJkcASXWMU5bllQgQvUmlKW0GIfhC9aM4J
# 04MeJOU1mHLjDcxwWpDD670AFmGRg/mMPxMywvY0HLUszWikcXNYxF1ph+LhlLI9
# f9R1qqkxggH5MIIB9QIBATBYMEExEzARBgoJkiaJk/IsZAEZFgNsYWIxFTATBgoJ
# kiaJk/IsZAEZFgVhbHBoYTETMBEGA1UEAxMKQWxwaGFTdWJDQQITcAAAAAeFdIhd
# 6FNaKwAAAAAABzAJBgUrDgMCGgUAoHgwGAYKKwYBBAGCNwIBDDEKMAigAoAAoQKA
# ADAZBgkqhkiG9w0BCQMxDAYKKwYBBAGCNwIBBDAcBgorBgEEAYI3AgELMQ4wDAYK
# KwYBBAGCNwIBFTAjBgkqhkiG9w0BCQQxFgQUHeu4SH+Zgy1QTG2JGI1Lwr8uLmYw
# DQYJKoZIhvcNAQEBBQAEggEAgPcrCrkk8WEmVEA1NGnmkTVwCTtCl+K0JnGdP4C5
# KYr9rd00jgH/E4FvJg+y6lUFcSD7hLOSFtPPEbW0vu7vtWf1L03hkeplhMmGNcDv
# 2Od2Gyd2AdeH8rrppIjtw2sOB1ZU750a68Fjj/2f5uhVK/139+NWIGVgZVTo9Ny5
# v5hPrl55DK+JRkC6f+MoJj6Lnz1ZH5kI5TMBqQcZNLf9J7K1lc0FHSnn7gGTSn4G
# 89WX6uIgw+F1UH1WwMofQXSwaVIuM7oS1+Cd0AVzV4USmssTkv3j537fHwEYCPy2
# 7nU5+QkndQrvD/y9O4ajQNL8qgPKGKpZjvDp0Pybz2mQKw==
# SIG # End signature block