Elisp: help on string operations

Elisp: help on string operations

[Karl Voit]

Hi!

For Memacs[1], I'd like to come up with a very fast Org-mode method to
open files independent of their location on your disk. I accomplished
everything necessary so far. However, I've got issues writing an elisp
function for extracting a file and sending it to a function that calls
the operating system app associated. My elisp knowledge is still too
bad :-(

What I've got is a string (from the lookup) which contains:
(1) nothing
(2) one line like "** <2008-06-17 21:43> [[file:/home/user/dir/2008-06-17 description of file.odp][2008-06-17 description of file.odp]]"
(3) multiple lines like (2) but with different files and links

I'd like to get a "Sorry" message for (1). Easy, if only I know how to
count lines in strings (as opposed to buffers).

For (2) I'd like to call my-open-in-external-app(string).

For (3), I'd like to use the first line just as in (2) as a starter. I
do have some ideas on gracious "error-recovering" on this one but
that's maybe too complicated to code for now: getting rid of
substrings delimited by not-'a-zA-Z0-9' from the end of the link
until a match is found; message in case there is no unique match which
could be found this way.

Could you please help me here?



The fragment I have so far is following but the regex seems to be
broken:

#+BEGIN_SRC elisp
    (let (
      (result (replace-regexp-in-string "\r?\n$" ""
                        (shell-command-to-string (concat "grep "
                                         "2008-06-17"
                                         " ~/org/memacs/files.org_archive")
                                     )
                        )
          )
      )
      (message (concat "result -> " result))
      (re-search-forward " \[\[.+\]\[" nil t 1)
      (let (
        (firstlink ((match-string 1)))
        )
        (message (concat "first link -> " firstlink))
       )
      )
#+END_SRC



[1] https://github.com/novoid/Memacs

-- 
All in all, one of the most disturbing things today is the definitive
fact that the NSA, GCHQ, and many more government organizations are
massively terrorizing the freedom of us and the next generations.
                                                  http://Karl-Voit.at

Re: Elisp: help on string operations

[Michael Heerdegen]

Hello Karl,

> I'd like to get a "Sorry" message for (1). Easy, if only I know how to
> count lines in strings (as opposed to buffers).

You could use `with-temp-buffer', insert the string and do your work
there.  Alternatively, go with `count-matches' or `split-string'.


>       (message (concat "result -> " result))

To avoid that a dynamically computed argument of `message' gets
interpreted with format specifier syntax considered, it's better to use
it like

        (message "%s" (compute-some-string-here))


>       (re-search-forward " \[\[.+\]\[" nil t 1)
                             ^^^^^^^^^^ 
That looks wrong.  You want to have a backslash char before the
brackets.  But since backslash is an escape character in the read syntax
of strings, you need to escape the backslash characters, which means
you need to double the backslashes.

Any questions left?


Regards,

Michael.

Re: Elisp: help on string operations

[Karl Voit]

* Michael Heerdegen <michael_heerdegen@web.de> wrote:
> Hello Karl,

Hallo Michael!

>> I'd like to get a "Sorry" message for (1). Easy, if only I know how to
>> count lines in strings (as opposed to buffers).
>
> You could use `with-temp-buffer', insert the string and do your work
> there.  Alternatively, go with `count-matches' or `split-string'.

Ah, so there are no string operations on strings in "memory" but
rather (lots of) string operations on strings in buffers. I see.

>>       (message (concat "result -> " result))
>
> To avoid that a dynamically computed argument of `message' gets
> interpreted with format specifier syntax considered, it's better to use
> it like
>
>         (message "%s" (compute-some-string-here))

Good point.

>>       (re-search-forward " \[\[.+\]\[" nil t 1)
>                              ^^^^^^^^^^ 
> That looks wrong.  You want to have a backslash char before the
> brackets.  But since backslash is an escape character in the read syntax
> of strings, you need to escape the backslash characters, which means
> you need to double the backslashes.

That's it, I see.

Man, I hate those different levels of escaping everywhere :-(

> Any questions left?

I got help from John Kitchin as well. So far I need to digest
everything I learned for now and try to come up with a solution that
works.

Danke!

-- 
All in all, one of the most disturbing things today is the definitive
fact that the NSA, GCHQ, and many more government organizations are
massively terrorizing the freedom of us and the next generations.
                                                  http://Karl-Voit.at

Re: Elisp: help on string operations

[Michael Heerdegen]

Karl Voit <devnull@Karl-Voit.at> writes:

> > You could use `with-temp-buffer', insert the string and do your work
> > there.  Alternatively, go with `count-matches' or `split-string'.
>
> Ah, so there are no string operations on strings in "memory" but
> rather (lots of) string operations on strings in buffers. I see.

No no, there are tons of string operations, `split-string' is one of
them.  But if you feel more comfortable with buffer operations, you can
go with temp buffers, unless speed is very crucial.

> Danke!

Aber gerne doch!


Michael.