On every nth (2) evaluation autoEval should invoke a function check[]. The thing which is supposed to listen for all Notebook Kernel Evaluation-s is this CellEvaluationFunction :> (check[]). I also tried and failed with SetOptions[nb,$Pre:>(check[])]; and SetOptions[nb,CellProlog:>(check[])]; and SetOptions[nb,CellEpilog:>(check[])];. All producecd same message that evaluation symbols given are not options of notebook object. Please help!

I prefer using TaggingRules for keeping persistent values but I could not get those to work either. If you think you have a better solution I'm all ears.

autoEval[ ] := NotebookAutoBackup[2]
autoEval[ n_Integer /; n > 0, objname_String : "autoback", 
   objloc_ : "Local"] :=  Block[{nb = EvaluationNotebook, x = 0},
   check[] := (++x; 
     If[x == n, (Echo@n; Print["check[]"]; 
       PersistentSymbol[objname, objloc] = 0), 
      PersistentSymbol[objname, objloc] = x]; Echo@x);
   CellEvaluationFunction :> (check[])

1 Answer 1


You could either use $Pre or $Post together with a global variable to keep count of how many times a cell is evaluated:

First you would initialize count and e.g. $Pre in s separate cell:

$Pre = (If[EvenQ[count++], Print["checking"]]; #) &;

Then the first cell evaluated will not print "checking". However, the second time you evaluate a cell "checking" is printed. This also happens every even number of times.

  • $\begingroup$ i really appreciate your help but i hesitate to use system-wide Kernel sniffers as they may interfere with other notebook tasks or projects. That's why I selected the given symbols as they can be set at the notebook level. $\endgroup$ Commented Jan 16, 2022 at 20:35
  • $\begingroup$ @DanielJHuber please disregard previous comment. although my example code shows n=2. This small value was given for expediency for testing function. The real-world value will be an arbitrarily selected positive integer probably less than 12. It will ultimately be a function that automatically creates a backup of InputNotebook at every nth Kernel evaluation. So how can we modify your solution for every nth evaluation? $\endgroup$ Commented Jan 25, 2022 at 16:01
  • $\begingroup$ Simply write: If[Mod[count++,n]==0,....] $\endgroup$ Commented Jan 25, 2022 at 17:03
  • $\begingroup$ @DanierlHuber thank you so much. you were very helpful. If you don';t mind would you have a look at another similar question I posted since? I;'ll tag your name to it if you dont mind. $\endgroup$ Commented Jan 25, 2022 at 18:50
  • $\begingroup$ Sorry, I can not see your question. $\endgroup$ Commented Jan 25, 2022 at 19:26

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