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I guess my programming working style is not unique. I develop programs one cell at a time, and when I have some confidence about what I did, I put all my mess together refining the code, building up functions from nailed constructs, scoping variables, etc.

That usually means being on a dirt road most of the time: evaluating a lot of cells, inspecting FullForms, checking different conditions, clicking the |Show More| button, etc.

Before I perform any action on my ongoing .nb I should save my work in advance.
But alas! My mind is weak, my memory fades and my feeble fingers are too quick for my tired eyes.
So, when I press Shift-Enter or |Show More| and my Front End hangs, I remember Michael Douglas' D-FENS character in "Falling Down" with utmost sympathy.

I would like an automatic way to save my input cells (not the output ones, as they could be really large) in a backup .nb file before and every time any computation is requested. How?

I must confess, my FrontEnd-fu is still in its teens.
I think $pre could be set to the desired command, but I don't know how to select only the input cells and save them programmatically.

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Related (possible duplicate): mathematica.stackexchange.com/q/6435/5 –  rm -rf Jul 27 '12 at 3:33
@R.M perhaps, but at first sight he is asking for a timed backup, which is not my target –  belisarius Jul 27 '12 at 3:36
There's the NotebookAutoSave option in the option inspector, or SetOptions[EvaluationNotebook[], NotebookAutoSave -> True]. This saves after each evaluation---not precisely what you asked for, but may be useful. –  Szabolcs Jul 27 '12 at 6:54
@Szabolcs Yes, two main differences: 1) I lost my last editing session 2) I don't like my "emergency backup" to overwrite the original file (as I perhaps made some mistake and don't want to permanently regret it) –  belisarius Jul 27 '12 at 13:40
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1 Answer

up vote 13 down vote accepted

The following definition to $Pre will save a copy of your notebook as filename.nb.backup.nb, where filename.nb is your original notebook and strip it of all output cells every time you evaluate a cell.

$Pre = With[
    {nb = NotebookPut[NotebookGet[EvaluationNotebook[]]]},
        FrontEnd`NotebookFind[nb, "Output", All, CellStyle, AutoScroll -> False], 
    NotebookSave[nb, NotebookFileName[] <> ".backup"];
] &
share|improve this answer
Seems to work pretty well! –  belisarius Jul 27 '12 at 4:05
It will change the result of evaluation in some special cases, for example when you evaluate an expression with Head Sequence or Unevaluated. Probably $PreRead would be more universal. –  Alexey Popkov Jul 27 '12 at 6:14
I don't like auto-save as it seems to inevitably result in the far more frustrating event of auto-saving just after an accidental deletion or other major incorrect change. By saving to a separate backup notebook you eliminate this. +1 –  Mr.Wizard Jul 27 '12 at 10:22
One of my fu-moves is Alt-/, which toggles comments. I save very frequently, and almost always modify code by copying it into a new cell and tweaking it there, commenting out the old version when necessary. An accident with the code being tweaked, then, is isolated to a copy, and I can always safely back up. This is a verbose style, and the final notebooks need a LOT of cleanup, but it's robust and easy on the fingers. –  Reb.Cabin Jul 31 '12 at 20:36
@Reb.Cabin Easier than an automated solution? ;) –  rm -rf Jul 31 '12 at 20:39
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