[GRASS-user] Re: Detect failure during batch job execution

[Hamish]

Tim Michelsen wrote:
> > Is there a way to detect whether an operation has succeeded or
> > failed? 

Yes. The program will exit with an "exit code". For GRASS modules this
will be "0" on success and "1" on fail. I am not sure what a Seg-fault
or other abnormal termination returns.

you can test the exit code for the last command from the Bash prompt
with "$?".

For example:
g.module
echo $?

g.module
RESULT=$?

if [ $RESULT -ne 0 ] ; then
  echo "it exited with an error"
fi



> > Or whether a vector layer exists or not?
> I am also interested into a solution on that.

g.findfile element=vector file=mapname

this will return various info about the map. You can set shell
variables with it directly:
eval `g.findfile element=vector file=roads`
echo "$fullname"

also the g.findfile return code is dependent on if the file was found
or not.

MAPNAME=roads
if [ `g.findfile element=vector file="$MAPNAME"` -eq 0 ] ; then
  d.vect $MAPNAME
fi

same as

eval `g.findfile element=vector file="$MAPNAME"`
if [ -n "$name" ] ; then
  d.vect $MAPNAME
fi


> I have been saving log to file using
> command > grass.log 2>&1
> 
> But this doensn't say anything about the result of the operation...

If it exits with an error there will be "ERROR: ...." or a
"Segmentation Fault" text. No output generally means everything was ok.
Note some modules may successfully exit haven written 0 features, e.g.
v.extract where="x != x".


Hamish



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