How can a remotely launched Applecsript display dialog?

Question

I have many Mac-computers running a variety of Mac OS X systems, including Tiger, Leopard, and Snow Leopard. On Tiger and Leopard, a Terminal bash-script could launch a compiled and saved Applescript (in /Applications/myLogout.app), which uses "say" to tell the user the system is going down in two-minutes. It then waits (delay 120), and then uses "say" again with this message, "System going down in 10 seconds". That's followed by a "display dialog" with the same message. The User could "Cancel" to stop the execution of the Applescript. If not, the applicaton proceeds to do cleanup work, like eliminating pesky /var/tmp files that invariablely end up as "Recovered" files or folders, and then it does "shut down".
I could remote login from another computer and execute this simple bash-script:
    #!/bin/bash
    if [ -x "/Applications/myLogout.app" ] ; then
       osascript /Applications/myLogout.app display >/dev/null 2>&1"
    else
       echo "Can't find Logout application"
    fi
    exit 0
This bash-script would wait at the osascript command until the Applescript terminated, which it did either because someone clicked Cancel in the dialog, or the "shut down" command occurred. My session then regained control, and usually was quickly terminated as a remote session.
But now, Snow Leopard wouldn't properly execute the Applescript. It always fails for lack of a WindowServer connection to my remote session.
I can't use launchd for this because of similar restrictions. For one thing, I have no clue who might be the active user on the target computer, and never had to worry about that because the "display dialog" was always presented to the "current" user. So, basically, Apple has removed the capability that existed in both Tiger and Leopard. Furthermore, their "solution" of using launchd doesn't cover this scenerio: - - remote launch of a UI application that warns the "current user", does a lot of cleanup work, and shuts down the computer.
I can do everything in a bash shell except present a dialog to give the "current user" a chance to Cancel. Basically, the myLogout application can be launched by the "current user", and since it doesn't have an input parameter, it doesn't wait or do the dialog. That works. But even when called from a bash-script WITHOUT a parameter (that's the "display" word in the sample), it still fails in Snow Leopard.
One final note: The "Product" listed with this post is NOT my Snow Leopard system, but it's NOT 10.4.11 either. I'm on 10.5.8

Answer 1

One of us is confused about something, and I'm not sure which of us it is.
What message are you trying to pass? If you want a formulaic "Shutdown in two minutes" message then code it directly into the script and don't bother with passing it. If you want a custom message that might change on different runs, then the easiest solution is to call a handler of the application on the remote machine and pass the message as a parameter.  just for an example, do this:
Put this script as a stay-open script application on the remote machine:
global idleInterval, message
on idle
          try
  -- error catching. when you call handler x(), first the script's run handler will run, then the idle handler, then x(), and the the idle handler in a loop. this prevents unset variable errors on the first pass.
  message
  idleInterval
          on error errstr
                    return 1
          end try
          if idleInterval is "Start" then
  say message
                    set idleInterval to 10
          else if idleInterval is 10 then
  say message
                    set idleInterval to 5
          else
                    display dialog "System wants to shut down"
                    set idleInterval to 1
                    quit
          end if
          return idleInterval
end idle
on x(textMessage)
          set idleInterval to "Start"
          set message to textMessage
end x
go back to the admin machine and run this command in the applescript editor:
tell application "ShowMsg" of machine remoteMachine
          x("Whoohoo!")
end tell
If it asks for authorization, give it. You can either save it in your keychain or we can work through the auth problem next.