From f0c3a7b25c0f960e7deae3721f1193771910d429 Mon Sep 17 00:00:00 2001
From: Markus Fleschutz <markus@fleschutz.de>
Date: Fri, 27 Aug 2021 15:35:34 +0200
Subject: [PATCH] Add check-subnet-mask.ps1

---
 Data/scripts.csv              |  1 +
 README.md                     |  1 +
 Scripts/check-subnet-mask.ps1 | 39 +++++++++++++++++++++++++++++++++++
 3 files changed, 41 insertions(+)
 create mode 100755 Scripts/check-subnet-mask.ps1

diff --git a/Data/scripts.csv b/Data/scripts.csv
index b55bfa09..d8b7c144 100644
--- a/Data/scripts.csv
+++ b/Data/scripts.csv
@@ -27,6 +27,7 @@ check-ipv4-address.ps1, checks the given IPv4 address for validity
 check-ipv6-address.ps1, checks the given IPv6 address for validity
 check-mac-address.ps1, checks the given MAC address for validity
 check-ping.ps1, checks the ping latency to the internet
+check-subnet-mask.ps1, checks the given subnet mask for validity
 check-swap-space.ps1, checks the swap space for free space left
 check-symlinks.ps1, checks every symlink in the given directory tree
 check-weather.ps1, checks the current weather for critical values
diff --git a/README.md b/README.md
index b0bb0f30..31489748 100644
--- a/README.md
+++ b/README.md
@@ -205,6 +205,7 @@ Mega Collection of PowerShell Scripts
 * [check-ipv4-address.ps1](Scripts/check-ipv4-address.ps1) - checks the given IPv4 address for validity
 * [check-ipv6-address.ps1](Scripts/check-ipv6-address.ps1) - checks the given IPv6 address for validity
 * [check-mac-address.ps1](Scripts/check-mac-address.ps1) - checks the given MAC address for validity
+* [check-subnet-mask.ps1](Scripts/check-subnet-mask.ps1) - checks the given subnet mask for validity
 * [check-weather.ps1](Scripts/check-weather.ps1) - checks the current weather for critical values
 * [convert-csv2txt.ps1](Scripts/convert-csv2txt.ps1) - converts the given CSV file to a text list
 * [convert-mysql2csv.ps1](Scripts/convert-mysql2csv.ps1) - converts the MySQL database table to a CSV file
diff --git a/Scripts/check-subnet-mask.ps1 b/Scripts/check-subnet-mask.ps1
new file mode 100755
index 00000000..d8e4d6a5
--- /dev/null
+++ b/Scripts/check-subnet-mask.ps1
@@ -0,0 +1,39 @@
+<#
+.SYNOPSIS
+	check-subnet-mask.ps1 [<address>]
+.DESCRIPTION
+	Checks the given subnet mask for validity
+.EXAMPLE
+	PS> .\check-subnet-mask.ps1 255.255.255.0
+.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
+	} else {
+		write-warning "Invalid subnet mask: $address"
+		exit 1
+	}
+} catch {
+	write-error "⚠️ Error in line $($_.InvocationInfo.ScriptLineNumber): $($Error[0])"
+	exit 1
+}