This kind of works

check_citrix_user.ps1

@@ -11,19 +11,52 @@
 #
 #################################################################################
 
-if ( (Get-PSSnapin -Name Citrix.XenApp.Commands -ErrorAction SilentlyContinue) -eq $null )
-{
-    Add-PSSnapin Citrix.XenApp.Commands
+$nscpBinary = "c:\program files\NSClient++\nscp.exe"
+$returnCode = "3" #Unknown by default 
+$nagiosHost = "mn-lx9.gsellc.local" # this is the host running the NSCA daemon
+$encryption = "3des" # set this to match nsca.cfg on the Nagios host
+$payloadLength = "4096" # set this to match your nsca daemon, the default is 512
+$nscaPassword = "somepassword" # set this to match nsca.cfg on the Nagios host
+$sourceHost = "CitrixFarm" # This needs to match the host you have configured in Nagios for these passive checks
+$userStringArray = @()
+
+
+function nagiosExit($returnCode, $statusOutput) {
+    Write-Host $statusOutput
+    Exit $returnCode
+}
+
+function sendNscaExit($returnCode, $statusoutput) {
 }
 
+if ( (Get-PSSnapin -Name Citrix.XenApp.Commands -ErrorAction SilentlyContinue) -eq $null ) {
+    Add-PSSnapin -Name Citrix.XenApp.Commands -ErrorAction SilentlyContinue
+    if ( (Get-PSSnapin -Name Citrix.XenApp.Commands -ErrorAction SilentlyContinue) -eq $null) {
+        nagiosExit "2" "Unable to load necessary Citrix PowerShell Snapins"    
+    }
+}
 
-$sendNscaBinary = 
-$loggedOnUsers =
-$returnCode = 3 #Unknown by default 
+$loggedOnUsers = Get-XASession -full  | where-object { ($_.ApplicationState -eq 'Active') } | select AccountName
 
 function sendNscaExit($returnCode, $statusoutput) {
 }
 
 foreach ($user in $loggedOnUsers) {
+    $userString = $user.AccountName
+    $userStringArray += $userString -replace '^.*\\',''
 }
+$userStringArray = $userStringArray | Select -Unique
 
+foreach ($user in $userStringArray) {
+    $nscpArgs = @("nsca",
+                  "host=$nagiosHost",
+                  "command=$user",
+                  "message=user $user is currently online",
+                  "result=OK",
+                  "encryption=$encryption",
+                  "payload-length=$payloadLength",
+                  "password=$nscaPassword",
+                  "source-host=$sourceHost")
+    &$nscpBinary $nscpArgs
+
+}