[ncl-talk] NCL exit code on failure

[Dennis Shea]

FYI: The previous emails have been added to JIRA ticket: NCL-1528


On Thu, Jul 7, 2016 at 10:09 AM, 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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