PowerShell/Docs/check-subnet-mask.md

## The *check-subnet-mask.ps1* Script

This PowerShell script checks the given subnet mask for validity.

## Parameters
```powershell
/home/mf/Repos/PowerShell/Scripts/check-subnet-mask.ps1 [[-address] <String>] [<CommonParameters>]

-address <String>
    Specifies the subnet mask to check
    
    Required?                    false
    Position?                    1
    Default value                
    Accept pipeline input?       false
    Accept wildcard characters?  false

[<CommonParameters>]
    This script supports the common parameters: Verbose, Debug, ErrorAction, ErrorVariable, WarningAction, 
    WarningVariable, OutBuffer, PipelineVariable, and OutVariable.
```

## Example
```powershell
PS> ./check-subnet-mask 255.255.255.0
✔️ subnet mask 255.255.255.0 is valid

```

## Notes
Author: Markus Fleschutz | License: CC0

## Related Links
https://github.com/fleschutz/PowerShell

## Source Code
```powershell
<#
.SYNOPSIS
	Checks the given subnet mask for validity
.DESCRIPTION
	This PowerShell script checks the given subnet mask for validity.
.PARAMETER address
	Specifies the subnet mask to check
.EXAMPLE
	PS> ./check-subnet-mask 255.255.255.0
	✔️ subnet mask 255.255.255.0 is valid
.LINK
	https://github.com/fleschutz/PowerShell
.NOTES
	Author: Markus Fleschutz | License: CC0
#>

param([string]$address = "")

function IsSubNetMaskValid { param([string]$IP)
	$RegEx = "^(254|252|248|240|224|192|128).0.0.0$|^255.(254|252|248|240|224|192|128|0).0.0$|^255.255.(254|252|248|240|224|192|128|0).0$|^255.255.255.(255|254|252|248|240|224|192|128|0)$"
	if ($IP -match $RegEx) {
		return $true
	} else {
		return $false
	}
}

try {
	if ($address -eq "" ) { $address = read-host "Enter subnet mask to validate" }

	if (IsSubNetMaskValid $address) {
		"✔️ subnet mask $Address is valid"
		exit 0 # success
	} else {
		write-warning "Invalid subnet mask: $address"
		exit 1
	}
} catch {
	"⚠️ Error in line $($_.InvocationInfo.ScriptLineNumber): $($Error[0])"
	exit 1
}
```

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