Re: [BUG] in org-property-drawer-re?

[Carsten Dominik <carsten.dominik@gmail.com>]

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On 1.10.2013, at 19:50, Thorsten Jolitz <tjolitz@gmail.com> wrote:

> 
> Hi List, 
> 
> for the navi-mode keyword-search for complete property drawers I copied
> 
> ,-----------------------
> | org-property-drawer-re
> `-----------------------
> 
> from org.el:
> 
> #+begin_src emacs-lisp
>  (concat "\\(" org-property-start-re "\\)[^\000]*\\("
> 	  org-property-end-re "\\)\n?")
> #+end_src
> 
> #+results:
> : \(^[ 	]*:PROPERTIES:[ 	]*$\)[^\\000]*\(^[ 	]*:END:[ 	]*$\)
> : ?
> 
> A bit unreadable, but you get the message ... here is my hopefully equivalent
> version: 
> 
> ,--------------------------------------------------------------
> | (:propertydrawer
> |   . (concat "\\(^[\\s\\t]*:PROPERTIES:[\\s\\t]*$\\)[^\\000]*"
> |             "\\(^[\\s\\t]*:END:[\\s\\t]*$\\)\\n?"))
> `--------------------------------------------------------------
> 
> But this did not match correctly in Bernt Hansens tutorial:

Indeed, this is a bad regular expression, it is too greedy and will
match all the way to the last :END: line it can find.  also, \\s is
wrong, it should be just a space, so "[ \t]". Luckily
this regular expression does not seem to be used in Org as far
as I can see....

> 
>    ,--------------------------------------------------------------------------
>    |  43::PROPERTIES:
>    |    ::CUSTOM_ID: Setup
>    |    ::END:
>    | 131::PROPERTIES:
>    |    ::CUSTOM_ID: OrgFiles
>    |    ::END:
>    | 185::PROPERTIES:
>    |    ::CUSTOM_ID: AgendaSetup
>    |    ::END:
>    |    :
>    |    :Here is my current =org-agenda-files= setup.
>    |    :#+begin_src emacs-lisp :tangle no
>    |    :  (setq org-agenda-files (quote ("~/git/org"
>    |    :                                 "~/git/org/client1"
>    |    :                                 "~/git/org/bzflag"
>    |    :                                 "~/git/client2")))
>    |    :#+end_src
>    |    :
>    |    :#+begin_src emacs-lisp :tangle yes :exports none
>    |    :  ;; The following setting is different from the document so that you
>    |    :  ;; can override the document org-agenda-files by setting your
>    |    :  ;; org-agenda-files in the variable org-user-agenda-files
>    |    :  ;;
>    |    :  (if (boundp 'org-user-agenda-files)
>    |    :      (setq org-agenda-files org-user-agenda-files)
>    |    :    (setq org-agenda-files (quote ("~/git/org"
>    |    :                                 "~/git/org/client1"
>    |    :                                 "~/git/org/bzflag"
>    |    :                                 "~/git/client2"))))
>    |    :  
>    |    :#+end_src
>    `--------------------------------------------------------------------------
> 
> I had to add two ?

You only need the first - the second is OK.

> after the * and delete the final \n 
> 
> ,-------------------------------------------------------------
> | (:propertydrawer
> | . (concat "\\(^[\\s\\t]*:PROPERTIES:[\\s\\t]*$\\)[^\\000]*?"
> |           "\\(^[\\s\\t]*:END:[\\s\\t]*?$\\)"))
> `-------------------------------------------------------------

Yes, you need the star to make it non-greedy.
However, you can leave the \n after you have corrected the
character class to "[ \t]" - it just means that
the \n will be part of the match, but still allow
for the possibility that the last line hits the end
of the buffer.

Ahhhh, regular expressions.  I think in my entire history
as a programmer, learning about regular expressions was
the biggest braintrip I ever had - still love them.

> 
> to get the desired results:
> 
>    ,---------------------------------
>    |  43::PROPERTIES:
>    |    ::CUSTOM_ID: Setup
>    |    ::END:
>    | 131::PROPERTIES:
>    |    ::CUSTOM_ID: OrgFiles
>    |    ::END:
>    | 185::PROPERTIES:
>    |    ::CUSTOM_ID: AgendaSetup
>    |    ::END:
>    | 234::PROPERTIES:
>    |    ::CUSTOM_ID: OrgFileStructure
>    |    ::END:
>    `---------------------------------
> 
> A bug in the regexp?
> 
> PS 
> Can anybody explain this marvelous construct in the regexp:
> 
> ,---------
> | [^\\000]
> `---------

This is just a cheep way to match any character at all, because \000 should
not be part of any string (in C it indicates the end of a string).
In principle you could put any character you are sure will not turn up,
but \000 seems to be the safest choice.  It is
faster (I think) than "\\(.\\|\n\\)*" because the first will
just run fast and streight with a table lookup while the
latter need to always alternate between two alternatives.
I have not timed it, though.

> 
> I often pondered about how to achieve its effect with other means, since
> I did not find it in the Emacs Lisp manual.

There you go - sometimes a brain is better than the Emacs manual :)

Regards

- Carsten

> 
> -- 
> cheers,
> Thorsten
> 
> 


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