[ncl-talk] NCL exit code on failure

[Andrew Dawson]

Sorry Kyle I misread your workaround example, it does indeed behave as you
described. I didn't know I could do this, interesting.

On 7 July 2016 at 18:03, Andrew Dawson <dawson at atm.ox.ac.uk> wrote:

> Thanks both
>
> Kyle - The workaround you suggest certainly returns 1, but does so also on
> success (i.e. when the line that causes an error is commented out) so this
> isn't particularly useful, unless I've misunderstood?
>
> Dennis - We re already using status_exit when we have detected an error
> condition we were expecting. However, I'm referring to a scenario where an
> un-handled error causes NCL to abort a script, it'd be great if this could
> return non-zero to the shell automatically.
>
> On 7 July 2016 at 17:09, Kyle Griffin <ksgriffin2 at wisc.edu> wrote:
>
>> I'm going to jump in here as well - I believe the status_exit(x) call
>> would do what is asked (if it can be inserted at the appropriate locations
>> that check for all possible conditions that could lead to an error being
>> thrown), but Andrew appears to ask about the default behavior of NCL, which
>> is to return exit code 0 regardless of what happened in execution.
>>
>> My interpretation (and something that I believe I experimented with a
>> couple years ago) was that this is a request for any "fatal: ..." errors to
>> throw a different exit code (presumably a simple 1), as do many other shell
>> programs to signal an unsuccessful execution.
>> I'm sure this is trickier behind the scenes than it sounds, but those of
>> us who use NCL for real-time or other automated processes would really
>> benefit from this simple change.
>>
>> Andrew - Now that I go back and look at a previous question on the same
>> topic (ticket NCL-1528), you should be able to add a "status_exit(1)" call
>> after your end statement to simulate this behavior in some cases, e.g.
>>
>> begin
>>     a = (/ 1 /)
>>     print(a(1))
>>     print("I won't be printed")
>>     exit
>> end
>> status_exit(1)
>>
>> While this should work for your example above, this workaround doesn't
>> catch errors that arise in other NCL functions (e.g. addfile), presumably
>> because they have their own begin/end block. Depending on where your errors
>> commonly arise, this might provide you some improvement in usability, but
>> the issue of error handling remains unaddressed in the wider scope of NCL
>> functions.
>>
>>
>> Kyle
>>
>> On Thu, Jul 7, 2016 at 9:14 AM Dennis Shea <shea at ucar.edu> wrote:
>>
>>> Would the following do what you want?
>>>
>>> http://www.ncl.ucar.edu/Document/Functions/Built-in/status_exit.shtml
>>>
>>> On Thu, Jul 7, 2016 at 5:21 AM, Andrew Dawson <dawson at atm.ox.ac.uk>
>>> wrote:
>>>
>>>> I'd like to know if it is possible to make NCL exit with a non-zero
>>>> status when it encounters a fatal error such as a subscrip error while
>>>> running a script? If not, could this be considered for a future version?
>>>>
>>>> Some background:
>>>>
>>>> We are running an NCL program in a batch job, and would like to detect
>>>> if the NCL program has failed. Within the program we have error checking
>>>> that calls status_exit with a non-zero status when we identify a fatal
>>>> error, and we can detect these errors from the shell script that calls NCL
>>>> via the process exit status $?. All fine so far.
>>>>
>>>> However, we discovered one of our programs may sometimes suffer a
>>>> run-time error due to incomplete data files, the form of this error is a
>>>> subscript out of range error, a fatal error that terminates the NCL
>>>> process. Unfortunately when NCL terminates it returns exit status 0, so we
>>>> cannot detect the failure directly in the shell. Instead we have to either
>>>> capture the output of the program and search for error messages, or
>>>> re-write the program so that this potential error condition is explicitly
>>>> checked and use a manual call to status_exit.
>>>>
>>>> A simple program to reproduce this is:
>>>>
>>>> begin
>>>>     a = (/ 1 /)
>>>>     print(a(1))
>>>>     print("I won't be printed")
>>>> end
>>>>
>>>> When run this program will terminate with a fatal error on the second
>>>> line, and the last line will not be executed, but the exit status of the
>>>> ncl process will be 0. It would be super convenient if the exit status was
>>>> non-zero in this case.
>>>>
>>>> I'm using NCL v6.3.0 on Linux x64
>>>>
>>>> Thanks
>>>> Andrew
>>>>
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>>
>
>
> --
> Dr Andrew Dawson
> Atmospheric, Oceanic & Planetary Physics
> Clarendon Laboratory
> Parks Road
> Oxford OX1 3PU, UK
> Tel: +44 (0)1865 282438
> Email: andrew.dawson at physics.ox.ac.uk
> Web Site: http://www2.physics.ox.ac.uk/contacts/people/dawson
>



-- 
Dr Andrew Dawson
Atmospheric, Oceanic & Planetary Physics
Clarendon Laboratory
Parks Road
Oxford OX1 3PU, UK
Tel: +44 (0)1865 282438
Email: andrew.dawson at physics.ox.ac.uk
Web Site: http://www2.physics.ox.ac.uk/contacts/people/dawson
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