Re: Re: Suppressing src block evaluationon publish?

["Eric Schulte" <schulte.eric@gmail.com>]

Dan Davison <dandavison7@gmail.com> writes:

> Loris Bennett <loris.bennett@fu-berlin.de> writes:
>
>> Erik Iverson <eriki@ccbr.umn.edu> writes:
>>
>>> Loris Bennett wrote:
>>>> Hi,
>>>>
>>>> I have an org file containing several src blocks which generate images
>>>> using ditaa. When I publish to PDF via LaTeX, the images are all
>>>> generated every time, which makes publishing rather slow.
>>>>
>>>> Is there some way to toggle the evaluation of the src blocks on and off
>>>> when the file is published?
>>>>
>>>
>>> You could try the :cache header argument, http://orgmode.org/org.html#cache
>>>
>>
>> Ah, thanks. There is a slight gotcha here, though.
>>
>> I added :cache yes to the source headers and exported again, but nothing
>> changed; all the images were generated again. Also, no SHA1 hash was
>> added to the +results header.
>>
>> After some fruitless fiddling I was about to write to the list again and
>> moan, when I did a slightly random C-c C-c in the begin_src line and,
>> hey presto, the hash was added to the results header. I then did this
>> for all the images and found that the image were no longer regenerated
>> on export, as advertised.
>
> Hi Loris,
>
> Yes. It does seem that it would be nice if in this situation, the first
> export added the SHA1s, and subsequent exports recognized that
> evaluation wasn't required. I think the reason this does not happen is
> that behind-the-scenes Org makes a copy of the buffer for export
> preprocessing (including src block evaluation). But Eric S is the expert
> -- he may have more to say here.
>

Yes, this is exactly the case.  Org-mode is very careful that the
process of exporting does not make any permanent changes to the original
org-mode file.  I agree this should be mentioned in the :cache
documentation.

Best -- Eric