Added logic to skip when Office is already installed

Install-OfficeCTR.ps1

@@ -17,17 +17,14 @@ at http://practical365.com
 Specify the UNC path to the network share that hosts the Office 365
 setup and configuration files.
 
-.PARAMETER OfficeVersion
-Specify the Office CTR version to deploy (e.g. 2013, or 2016)
-
 .PARAMETER SKU
 Specify the the Office CTR SKU to deploy (e.g. ProPlus, Business)
 
-.PARAMETER 
+.PARAMETER Channel
+Specify the build channel to deploy (e.g. Current, Deferred)
 
 .EXAMPLE
-.\Verb-NounsAndThings.ps1
+.\Install-OfficeCTR.ps1 -InstallRoot \\mgmt\Installs\OfficeCTR -SKU ProPlus -Channel Deferred
-What does this example do...
 
 .NOTES
 Written by: Paul Cunningham
@@ -69,6 +66,8 @@ param (
 	)
 
 
+function DoInstall {
+
     $ConfigurationXML = "$($InstallRoot)\$($SKU)\$($Channel)\configuration.xml"
 
     If (!(Test-Path $ConfigurationXML)) {
@@ -98,3 +97,32 @@ try {
     catch {
         Write-Warning $_.Exception.Message
     }
+
+}
+
+#Check if Office is already installed, as indicated by presence of registry key
+$RegistryPath = 'HKLM:\SOFTWARE\Microsoft\Office\16.0\ClickToRunStore\Packages\{9AC08E99-230B-47e8-9721-4577B7F124EA}'
+
+if (Test-Path $RegistryPath) {
+    #Check for children
+
+    $Item = Get-ItemProperty -Path $RegistryPath
+
+    if (!($Item.'(default)' -eq $null)) {
+        #Office is installed, according to registry key. Nothing further to do.
+        EXIT
+    }
+    else {
+        #Registry key exists but default value is empty, install needed
+        DoInstall
+    }
+}
+else {
+    #Registry key doesn't exist, install needed
+    DoInstall
+}
+
+
+
+
+