Public/Test-IPv4MaskString.ps1

function Test-IPv4MaskString {
    <#
        .SYNOPSIS
            Tests whether an IPv4 network mask string (e.g., "255.255.255.0") is valid.
        .DESCRIPTION
            Tests whether an IPv4 network mask string (e.g., "255.255.255.0") is valid.
        .PARAMETER MaskString
            Specifies the IPv4 network mask string (e.g., "255.255.255.0").
        .EXAMPLE
            Test-IPv4MaskString -MaskString "255.255.255.0"
    #>

    [CmdletBinding(ConfirmImpact = 'Medium')]
    Param
    (
        [Parameter(Mandatory = $false,
            ValueFromPipeline = $true,
            ValueFromPipelineByPropertyName = $true,
            ValueFromRemainingArguments = $false,
            HelpMessage = "Specifies the IPv4 network mask string (e.g., 255.255.255.0)",
        Position = 1)]
        [String] $MaskString
    )
    Begin {
        Write-Verbose -Message '|=> ************************************************************************ <=|'
        Write-Verbose -Message (Get-Date).ToShortDateString()
        Write-Verbose -Message (' Starting: {0}' -f $MyInvocation.Mycommand)

        #display PSBoundparameters formatted nicely for Verbose output
        $NL   = "`n"  # New Line
        $HTab = "`t"  # Horizontal Tab
        [string]$pb = ($PSBoundParameters | Format-Table -AutoSize | Out-String).TrimEnd()
        Write-Verbose -Message "Parameters used by the function... $NL$($pb.split($NL).Foreach({"$($HTab*4)$_"}) | Out-String) $NL"

    }
    Process {
        $validBytes = '0|128|192|224|240|248|252|254|255'
        $maskPattern = ('^((({0})\.0\.0\.0)|'      -f $validBytes) +
             ('(255\.({0})\.0\.0)|'      -f $validBytes) +
             ('(255\.255\.({0})\.0)|'    -f $validBytes) +
             ('(255\.255\.255\.({0})))$' -f $validBytes)
        $MaskString -match $maskPattern
    }
    End {
        Write-Verbose -Message "Function $($MyInvocation.InvocationName) finished."
        Write-Verbose -Message ''
        Write-Verbose -Message '-------------------------------------------------------------------------------'
        Write-Verbose -Message ''
    }
}