functions/configuration/Get-DbatoolsConfigValue.ps1

function Get-DbatoolsConfigValue {
    <#
    .SYNOPSIS
        Returns the configuration value stored under the specified name.
 
    .DESCRIPTION
        Returns the configuration value stored under the specified name.
        It requires the full name (<Module>.<Name>) and is usually only called by functions.
 
    .PARAMETER FullName
        The full name (<Module>.<Name>) of the configured value to return.
 
    .PARAMETER Fallback
        A fallback value to use, if no value was registered to a specific configuration element.
        This basically is a default value that only applies on a "per call" basis, rather than a system-wide default.
 
    .PARAMETER NotNull
        By default, this function returns null if one tries to retrieve the value from either a Configuration that does not exist or a Configuration whose value was set to null.
        However, sometimes it may be important that some value was returned.
        By specifying this parameter, the function will throw an error if no value was found at all.
 
    .NOTES
        Tags: Config, Module
        Author: Friedrich Weinmann (@FredWeinmann)
 
        Website: https://dbatools.io
        Copyright: (c) 2018 by dbatools, licensed under MIT
        License: MIT https://opensource.org/licenses/MIT
 
    .EXAMPLE
        PS C:\> Get-DbatoolsConfigValue -Name 'System.MailServer'
 
        Returns the configured value that was assigned to the key 'System.MailServer'
 
    .EXAMPLE
        PS C:\> Get-DbatoolsConfigValue -Name 'Default.CoffeeMilk' -Fallback 0
 
        Returns the configured value for 'Default.CoffeeMilk'. If no such value is configured, it returns '0' instead.
 
    #>

    [Diagnostics.CodeAnalysis.SuppressMessageAttribute("PSPossibleIncorrectComparisonWithNull", "")]
    [CmdletBinding()]
    param (
        [Alias('Name')]
        [Parameter(Mandatory)]
        [string]$FullName,
        [object]$Fallback,
        [switch]$NotNull
    )
    Test-DbaDeprecation -DeprecatedOn "1.0.0" -EnableException:$false -Alias Get-DbaConfigValue
    $FullName = $FullName.ToLowerInvariant()

    $temp = $null
    $temp = [Sqlcollaborative.Dbatools.Configuration.ConfigurationHost]::Configurations[$FullName].Value
    if ($temp -eq $null) { $temp = $Fallback }

    if ($NotNull -and ($temp -eq $null)) {
        Stop-Function -Message "No Configuration Value available for $Name" -EnableException $true -Category InvalidData -Target $FullName
    } else {
        return $temp
    }
}