Ensure AppleScript App Quits

Question

I have an AppleScript saved as a run only app which I call every hour from launchd.
Most of the time it works fine, but occasionally something causes the app not to quit when it's done its thing.  This means that next time an error is thrown and the process does not run (so it fails until I force quit the app).
I have tried wrapping the whole script in a try...with timeout...end timeout...on error return...end try structure but that makes no difference.
The core of the script is a run shell script that calls a perl script which in turn gets data from a web site.  I have tried nesting a try...on errror...end try around this that simply sets the content of the variable that should be populated from the script in the event that any error occurs.
The final part of the script is opening a [text] file and inserting a few lines at the top.  Again I have tried wrapping this in a try...on error return...end try stricture.
None of these efforts seems to have any effect.  However, I can't get the script to fail when I run it from the ApplScript Editor.
Would I be better to use osascript to call a script rather than the app, or am I doing something more fundamental wrong?

Answer 1

I'm not trying to be coy either, but I don't see that posting the whole script is going to help particularly because the perl script uses WWW::Mechanize to get data from a website where I have to provide user credentials - hence, it will not be possible to run it without those credentials.
The expectation is that I will get approximately ten lines of data back (which I put into a local variable).  I then use an offset check to determine whether a particular string is present.  If it is present, I then go on to compose a message (using Messages) to send to myself.
Regardless of the content, I open a local text file and insert the web response at the beginning of the file (as an activity log).  The file is then closed for access and that's it.
I have only once seen an error when I ran the script from the AS Editor and this seemed to indicate a problem with the site's availability - so when Mechanize couldn't find any identifiable data, it threw an error.
The app is not saved as stay open, but it does.  All I can say for certain is that the log file does not get written to, so I suspect that the problem lies with the perl script.  It is for that reason that I wrapped it in a try...with timeout structure.  (My understanding of the timeout, is that if script execution fails to complete within the timeout an error will be thrown, so this is picked-up by the try...on error.  That understanding may be wrong.)
So, after all that, here is the script [with a single hard-coded address obscured for privacy]:
try
          set desktopPath to (path to desktop) as alias
          set FlightCheckLog to (desktopPath as text) & "FlightCheckLog.txt"
          set targetList to {"Sep-7", "Sep-8", "Sep-9", "Sep-10"}
          tell application "Messages"
                    set theBuddy to buddy id "<OBSCURED>"
          end tell
          set messageSent to false
          try
                    with timeout of 300 seconds
                              set theFlights to do shell script "~/Documents/perl/FilghtCheck.pl -x -c J -d 2013-09-07 ATH-LHR"
                    end timeout
          on error
                    set theFlights to ""
          end try
          repeat with theDate in targetList
                    set theOffset to (offset of theDate in theFlights)
                    if theOffset is not 0 then
                              set theFlight to text (theOffset - 5) thru end of theFlights
                              set theReturn to (offset of return in theFlight)
                              set theFlight to text 1 thru (theReturn - 1) of theFlight
                              tell application "Messages"
  send theFlight to theBuddy
                                        set messageSent to true
                              end tell
                    end if
          end repeat
          try
                    set theFile to open for access FlightCheckLog with write permission
  get eof theFile
                    if result > 0 then
                              set fileText to read theFile
  set eof theFile to 0
                    else
                              set fileText to ""
                    end if
                    if messageSent then
                              write ((current date) & return & theFlights & return & "MESSAGE SENT" & return & return & fileText) as text to theFile
                    else
                              write ((current date) & return & theFlights & return & return & fileText) as text to theFile
                    end if
  close access theFile
          on error
                    return
          end try
on error
          return
end try