functions/Get-DbaAgListener.ps1

function Get-DbaAgListener {
    <#
        .SYNOPSIS
            Outputs the name of the Listener for the Availability Group(s) found on the server.
 
        .DESCRIPTION
            Default view provides most common set of properties for information on the database in an Availability Group(s).
 
            Information returned on the database will be specific to that replica, whether it is primary or a secondary.
 
            This command will return an SMO object, but it is the AvailabilityDatabases object and not the Server.Databases object.
 
        .PARAMETER SqlInstance
            The SQL Server instance. Server version must be SQL Server version 2012 or higher.
 
        .PARAMETER SqlCredential
            Allows you to login to servers using SQL Logins instead of Windows Authentication (AKA Integrated or Trusted).
 
        .PARAMETER AvailabilityGroup
            Specify the Availability Group name that you want to get information on.
         
        .PARAMETER Listener
            Specify the Listener name that you want to get information on.
 
        .PARAMETER Silent
            If this switch is enabled, the internal messaging functions will be silenced.
 
        .NOTES
            Tags: DisasterRecovery, AG, AvailabilityGroup, Replica
            Author: Viorel Ciucu (@viorelciucu)
 
            Website: https://dbatools.io
            Copyright: (C) Chrissy LeMaire, clemaire@gmail.com
            License: GNU GPL v3 https://opensource.org/licenses/GPL-3.0
 
        .LINK
            https://dbatools.io/Get-DbaAgListener
 
        .EXAMPLE
            Get-DbaAgListener -SqlInstance sqlserver2014a
 
            Returns basic information on the listener found on sqlserver2014a
 
        .EXAMPLE
            Get-DbaAgListener -SqlInstance sqlserver2014a -AvailabilityGroup AG-a
 
            Returns basic information on the listener found on sqlserver2014a in the Availability Group AG-a
 
    #>

    [CmdletBinding()]
    param (
        [parameter(Mandatory = $true, ValueFromPipeline = $true)]
        [Alias("ServerInstance", "SqlServer")]
        [DbaInstanceParameter[]]$SqlInstance,
        [PSCredential][System.Management.Automation.CredentialAttribute()]
        $SqlCredential,
        [parameter(ValueFromPipeline = $true)]
        [object[]]$AvailabilityGroup,
        [object[]]$Listener,
        [switch]$Silent
    )

    process {
        foreach ($serverName in $SqlInstance) {
            try {
                $server = Connect-SqlInstance -SqlInstance $serverName -SqlCredential $SqlCredential -MinimumVersion 11
            }
            catch {
                Stop-Function -Message "Failure" -Category ConnectionError -ErrorRecord $_ -Target $instance -Continue
            }

            if ($server.IsHadrEnabled -eq $false) {
                Stop-Function -Message "Availability Group (HADR) is not configured for the instance: $serverName." -Target $serverName -Continue
            }

            $ags = $server.AvailabilityGroups
            if ($AvailabilityGroup) {
                $ags = $ags | Where-Object Name -in $AvailabilityGroup
            }
            
            if ($Listener) {
                $ags = $ags | Where-Object AvailabilityGroupListeners -match $Listener
                if ($ags.Length -eq 0) {
                    Stop-Function -Message "We could not find the listener $Listener on $serverName" -Target $serverName -Continue
                }
            }

            foreach ($ag in $ags) {     
                
                $Listener = $ag.AvailabilityGroupListeners
                $defaults = 'Parent as AvailabilityGroupName','Name as ListenerName','PortNumber','ClusterIPConfiguration'
                
                Select-DefaultView -InputObject $Listener -Property $defaults
            }

        }
    }
}