Re: gnuplot error code

[sfeam <sf...@us...>]

On Saturday, 04 February 2017 09:38:31 AM pl...@pi... wrote:
> On 04/02/17 04:14, sfeam wrote:
> > On Saturday, 04 February 2017 01:17:25 AM :	pl...@pi... wrote:
> >> Hi,
> >>
> >> I am calling gnuplot as a child process and need to conditionally return
> >> a non zero error code in some circumstances. From a quick search it
> >> seems that this is not possible, It always returns zero: yet that seems
> >> a little surprising.
> >>
> >> perl -e 'system("gnuplot -e \"exit 1;\""); print "$?\n"'
> >>
> >> The only way I can get a non zero result is if there is a parsing error
> >> in the gnuplot commands.
> >>
> >> I am using gnuplot to display real time data on a server and it would be
> >> good to be able to do some basic error trapping, not least for
> >> debugging. Is there a way to do this?
> >
> > Correct. There is no way to control the gnuplot exit value.
> >
> >
> 
> Thanks for the confirmation, Ethan.
> 
> Would this be a worthwhile feature to add? 

Sure.  But I have no idea how we would do it.
Adding a command "exit <status>" would not help so far as I can see,
because in order to execute that command the program must be
in a non-error state. So the only code it makes sense to emit is 0.

If there is a serious error like segfault or divide-by-zero the
program exits via the system fault-handling and gnuplot's normal
exit routine is not invoked.  If there is a non-fatal error
(read past end-of-file, say) gnuplot handles this internally and
by the time it is ready to parse a new command like "exit" the
error state no longer exists.

What sort of error do you imagine reporting?

	Ethan



> I'm thinking of something 
> like the awk exit which allows an optional  integer argument to  return.
> 
> if ( ! happy ) { print "not happy" ; exit 1; )
> 
> gnuplot is an excellent tool for plotting real time data on embedded 
> devices to provide real time graphic output but obviously the 
> possibility to exit with an error condition can be helpful, firstly in 
> debugging and also trapping possible error conditions with a meaningful 
> response should they happen.
> 
> The current behaviour is just jexit 0 , for backwards compat, some 
> thought would need to be given to current non zero return in case of a 
> syntax error in a gnuplot script but this does not seem to raise any 
> conflict for those trapping current behaviour.
> 
> Peter.
> 
> 
> 
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