converting octal escape sequences to utf-8 and back

converting octal escape sequences to utf-8 and back

[Roland Winkler]

I am trying to use emacs to interface with a program that treats
utf-8 characters in its input and output as octal escape sequences.
So the program's output contains ascii strings like "\302\247",
which I want to display within Emacs as "§". Likewise, I want to
feed text containing utf-8 characters such as "§" into this program.
So I need to convert these utf-8 characters back to their respective
octal escape sequences. What is the proper way to achieve this?

Thanks a lot,

Roland

Re: converting octal escape sequences to utf-8 and back

[Leo]

On 2011-05-29 08:27 +0800, Roland Winkler wrote:
> I am trying to use emacs to interface with a program that treats
> utf-8 characters in its input and output as octal escape sequences.
> So the program's output contains ascii strings like "\302\247",
> which I want to display within Emacs as "§". Likewise, I want to
> feed text containing utf-8 characters such as "§" into this program.
> So I need to convert these utf-8 characters back to their respective
> octal escape sequences. What is the proper way to achieve this?
>
> Thanks a lot,
>
> Roland

Are these functions useful?

encode-coding-string, decode-coding-string
encode-coding-region, decode-coding-region

Leo

Re: converting octal escape sequences to utf-8 and back

[Michael Welsh Duggan]

Leo <sdl.web@gmail.com> writes:

> On 2011-05-29 08:27 +0800, Roland Winkler wrote:
>> I am trying to use emacs to interface with a program that treats
>> utf-8 characters in its input and output as octal escape sequences.
>> So the program's output contains ascii strings like "\302\247",
>> which I want to display within Emacs as "§". Likewise, I want to
>> feed text containing utf-8 characters such as "§" into this program.
>> So I need to convert these utf-8 characters back to their respective
>> octal escape sequences. What is the proper way to achieve this?
>>
>> Thanks a lot,
>>
>> Roland
>
> Are these functions useful?
>
> encode-coding-string, decode-coding-string
> encode-coding-region, decode-coding-region

As Leo says:

(encode-coding-string "§" 'utf-8)
"\302\247"
(decode-coding-string "\302\247" 'utf-8)
"§"

-- 
Michael Welsh Duggan
(md5i@md5i.com)

Re: converting octal escape sequences to utf-8 and back

[Roland Winkler]

On Sun May 29 2011 Michael Welsh Duggan wrote:
> As Leo says:
> 
> (encode-coding-string "§" 'utf-8)
> "\302\247"
> (decode-coding-string "\302\247" 'utf-8)
> "§"

The decoding seems to work fine this way, but not the encoding.
If I start out with the 8-character ascii string "\302\247" the
following does not give me back this 8-character string:

(with-temp-file "~/foo.txt"
    (insert (encode-coding-string
             (decode-coding-string "\302\247" 'utf-8) 'utf-8)))

This will ask me for the coding system I want, suggesting the
default 'raw-text. Then I end up with a file that has only two
bytes, instead of the eight bytes I want. 

What am I doing wrong? Do I need anything else for this?

Roland

Re: converting octal escape sequences to utf-8 and back

[Michael Welsh Duggan]

"Roland Winkler" <winkler@gnu.org> writes:

> On Sun May 29 2011 Michael Welsh Duggan wrote:
>> As Leo says:
>> 
>> (encode-coding-string "§" 'utf-8)
>> "\302\247"
>> (decode-coding-string "\302\247" 'utf-8)
>> "§"
>
> The decoding seems to work fine this way, but not the encoding.
> If I start out with the 8-character ascii string "\302\247" the
> following does not give me back this 8-character string:
>
> (with-temp-file "~/foo.txt"
>     (insert (encode-coding-string
>              (decode-coding-string "\302\247" 'utf-8) 'utf-8)))
>
> This will ask me for the coding system I want, suggesting the
> default 'raw-text. Then I end up with a file that has only two
> bytes, instead of the eight bytes I want. 

(with-temp-file "~/foo.txt"
  (insert (substring (prin1-to-string 
                      (encode-coding-string 
                       (decode-coding-string "\302\247" 'utf-8)'utf-8)) 
                     1 -1)))

-- 
Michael Welsh Duggan
(md5i@md5i.com)

Re: converting octal escape sequences to utf-8 and back

[Eli Zaretskii]

> From: Michael Welsh Duggan <md5i@md5i.com>
> Date: Sun, 29 May 2011 01:40:54 -0400
> Cc: Roland Winkler <winkler@gnu.org>
> 
> As Leo says:
> 
> (encode-coding-string "§" 'utf-8)
> "\302\247"

This is an illusion: what is produced are 2 bytes, but when Emacs
inserts that into the buffer where the results are displayed, the
bytes are represented as ASCII strings.  Try writing the result to a
file (e.g., with write-region) and you will see that what ends up in
the file is simply the UTF-8 encoding of the character.  This is not
what the OP wanted.

IOW, encode-coding-string produces the encoding specified by its 3rd
argument, not its ASCII representation.

Re: converting octal escape sequences to utf-8 and back

[Roland Winkler]

On Sun, May 29 2011, Eli Zaretskii wrote:
> This is an illusion: what is produced are 2 bytes, but when Emacs
> inserts that into the buffer where the results are displayed, the
> bytes are represented as ASCII strings.  Try writing the result to a
> file (e.g., with write-region) and you will see that what ends up in
> the file is simply the UTF-8 encoding of the character.  This is not
> what the OP wanted.
>
> IOW, encode-coding-string produces the encoding specified by its 3rd
> argument, not its ASCII representation.

...So it seems that emacs knows already what I would like to have (at
least its display engine). How can I achieve that I actually get this in
an output file, too? Are there some formulas that allow one to calculate
these octal sequences? Then it should be possible to construct the ascii
character sequences, too.

Roland

Re: converting octal escape sequences to utf-8 and back

[Eli Zaretskii]

> From: Roland Winkler <winkler@gnu.org>
> Date: Sun, 29 May 2011 01:58:30 -0500
> 
> > IOW, encode-coding-string produces the encoding specified by its 3rd
> > argument, not its ASCII representation.
> 
> ...So it seems that emacs knows already what I would like to have (at
> least its display engine).

Nitpicking: It's not the display engine that does that, it's
eval-last-sexp.

> How can I achieve that I actually get this in an output file, too?
> Are there some formulas that allow one to calculate these octal
> sequences?

This should do what you want:

  (with-output-to-string (princ (encode-coding-string STRING 'utf-8)))

(the STRING argument should be the entire string that you want to send
to that program of yours).

But this is crazy, IMO: Lisp code should not need to jump through the
hoops like that to produce such an octal representation.  TRT is to
have a special encoding for this, then you could simply say

  (encode-coding-string STRING 'foo)

or even just

  (encode-coding-region START END 'foo)

because I presume that your original text comes from some buffer.

Re: converting octal escape sequences to utf-8 and back

[Roland Winkler]

On Sun May 29 2011 Eli Zaretskii wrote:
> This should do what you want:
> 
>   (with-output-to-string (princ (encode-coding-string STRING 'utf-8)))
> 
> (the STRING argument should be the entire string that you want to send
> to that program of yours).

Thank you. This seems to do what I want.

> But this is crazy, IMO: Lisp code should not need to jump through the
> hoops like that to produce such an octal representation.  TRT is to
> have a special encoding for this

For what I want to do, this seems to be not a bottleneck. (I am
playing with a frontend for the program djvused.) -- I do not know
how common are rare my problem is to justify a new encoding for it.
Certainly, a new encoding goes much beyond my knowledge of these
things.

The web page http://billposer.org/Software/ListOfRepresentations.html
lists about 30 unicode escape formats which emacs possibly could
implement. I do not know how many of these formats are possibly
already implemented. For most of them this web page includes example
programs using it; and some of these programs appear to be more
common. For the particular format I need, this web page simply says
"used by various programs". So I don't know how common my particular
problem might be to justify such an effort. Maybe some other formats
described there would be yet more helpful for other people.

Roland

Re: converting octal escape sequences to utf-8 and back

[Thien-Thi Nguyen]

() Roland Winkler <winkler@gnu.org>
() Sun, 29 May 2011 01:58:30 -0500

   How can I achieve that I actually get this in
   an output file, too?

In *scratch*, i bind ‘C-j’ to ‘ppq’[0], reproduced here:

  (defun ppq (&optional replace)
    (interactive "P")
    (when replace
      (delete-region (point) (progn (forward-sexp 1) (point))))
    (save-excursion
      (insert "\n")
      (pp-eval-last-sexp t)
      (when (bolp)
        (delete-char -1))))

The function ‘pp-eval-last-sexp’ winds up calling ‘pp-to-string’.
You can finangle it to achieve the desired result like so:

  (defvar pp-to-string-double-backslash t)
  
  (defun pp-to-string (object)
    "Return a string containing the pretty-printed representation of OBJECT.
  OBJECT can be any Lisp object.  Quoting characters are used as needed
  to make output that `read' can handle, whenever this is possible."
    (with-current-buffer (generate-new-buffer " pp-to-string")
      (unwind-protect
          (progn
            (lisp-mode-variables nil)
            (set-syntax-table emacs-lisp-mode-syntax-table)
            (let ((print-escape-newlines pp-escape-newlines)
                  (print-quoted t))
              (prin1 object (current-buffer)))
            (pp-buffer)
            ;; Begin finangling.
            (when pp-to-string-double-backslash
              (goto-char (point-min))
              (while (search-forward "\\" nil t)
                (replace-match "\\\\" t t)))
            ;; End finangling.
            (buffer-string))
        (kill-buffer (current-buffer)))))

This was the five-minute top-down way.  The cleaner bottom-up way
is to specify an appropriate PRINTCHARFUN to ‘prin1’, which is at
the heart of all pp funcs.  Perhaps someone else can post that.

__________________________________________________________________________________
[0] http://www.gnuvola.org/software/personal-elisp/dist/lisp/prog-env/ppq.el

Re: converting octal escape sequences to utf-8 and back

[Eli Zaretskii]

> Date: Sat, 28 May 2011 19:27:51 -0500
> From: "Roland Winkler" <winkler@gnu.org>
> 
> I am trying to use emacs to interface with a program that treats
> utf-8 characters in its input and output as octal escape sequences.
> So the program's output contains ascii strings like "\302\247",
> which I want to display within Emacs as "§". Likewise, I want to
> feed text containing utf-8 characters such as "§" into this program.
> So I need to convert these utf-8 characters back to their respective
> octal escape sequences. What is the proper way to achieve this?

A new coding-system?

Re: converting octal escape sequences to utf-8 and back

[Roland Winkler]

On Sun May 29 2011 Eli Zaretskii wrote:
> > Date: Sat, 28 May 2011 19:27:51 -0500
> > From: "Roland Winkler" <winkler@gnu.org>
> > I am trying to use emacs to interface with a program that treats
> > utf-8 characters in its input and output as octal escape sequences.
> > So the program's output contains ascii strings like "\302\247",
> > which I want to display within Emacs as "§". Likewise, I want to
> > feed text containing utf-8 characters such as "§" into this program.
> > So I need to convert these utf-8 characters back to their respective
> > octal escape sequences. What is the proper way to achieve this?
> 
> A new coding-system?

I cannot claim I understand these things. But I thought that there
was some kind of a "conversion formula" that allows one to calculate
the octal sequence for any utf-8 character and also the opposite,
get the character given the octal sequence. Is this true?

There is a little tool uni2ascii which seems to implement this, see

http://directory.fsf.org/project/uni2ascii/

But if possible I would like to achieve this from within Emacs.

Roland

Re: converting octal escape sequences to utf-8 and back

[Randal L. Schwartz]

>>>>> "Roland" == Roland Winkler <winkler@gnu.org> writes:

Roland> So the program's output contains ascii strings like "\302\247",

Minor nit, but "ASCII" doesn't include anything above \177.  If it has a
high-bit, it has to be something like latin-1, or (in your case) raw
UTF-8 bytes.

-- 
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc.
See http://methodsandmessages.posterous.com/ for Smalltalk discussion

Re: converting octal escape sequences to utf-8 and back

[Harald Hanche-Olsen]

[merlyn@stonehenge.com (Randal L. Schwartz) (2011-05-30 22:39:51 UTC)]

> >>>>> "Roland" == Roland Winkler <winkler@gnu.org> writes:
> 
> Roland> So the program's output contains ascii strings like "\302\247",
> 
> Minor nit, but "ASCII" doesn't include anything above \177.  If it has a
> high-bit, it has to be something like latin-1, or (in your case) raw
> UTF-8 bytes.

True, but given the octal escape sequences mentioned in the subject I
thought he meant the string that is denoted "\\302\\247" in elisp,
which is indeed ASCII. But that could be a misunderstanding on my
part.

- Harald

Re: converting octal escape sequences to utf-8 and back

[Randal L. Schwartz]

>>>>> "Harald" == Harald Hanche-Olsen <hanche@math.ntnu.no> writes:

Harald> True, but given the octal escape sequences mentioned in the subject I
Harald> thought he meant the string that is denoted "\\302\\247" in elisp,
Harald> which is indeed ASCII.

No, the string "\302\247" is not ASCII.  It's 8-bit-something-or-other.

-- 
Randal L. Schwartz - Stonehenge Consulting Services, Inc. - +1 503 777 0095
<merlyn@stonehenge.com> <URL:http://www.stonehenge.com/merlyn/>
Smalltalk/Perl/Unix consulting, Technical writing, Comedy, etc. etc.
See http://methodsandmessages.posterous.com/ for Smalltalk discussion

Re: converting octal escape sequences to utf-8 and back

[PJ Weisberg]

On Tuesday, May 31, 2011, Randal L. Schwartz <merlyn@stonehenge.com> wrote:
>>>>>> "Harald" == Harald Hanche-Olsen <hanche@math.ntnu.no> writes:
>
> Harald> True, but given the octal escape sequences mentioned in the subject I
> Harald> thought he meant the string that is denoted "\\302\\247" in elisp,
> Harald> which is indeed ASCII.
>
> No, the string "\302\247" is not ASCII.  It's 8-bit-something-or-other.

ASCII definitely *does* include the character \, and all the digits
0-9, in only 7 bits.

-- 

-PJ

Re: converting octal escape sequences to utf-8 and back

[Stefan Monnier]

> I am trying to use emacs to interface with a program that treats
> utf-8 characters in its input and output as octal escape sequences.
> So the program's output contains ascii strings like "\302\247",
> which I want to display within Emacs as "§". Likewise, I want to
> feed text containing utf-8 characters such as "§" into this program.
> So I need to convert these utf-8 characters back to their respective
> octal escape sequences. What is the proper way to achieve this?

You can try to convert the \302 and \247 to/from bytes by using `read'
and `prin1' (since Emacs also uses such a notation for its own Elisp
strings).  As for converting those bytes to/from chars, just use
(en|de)code-coding-string.


        Stefan

Re: converting octal escape sequences to utf-8 and back

[Roland Winkler]

On Mon May 30 2011 Stefan Monnier wrote:
> You can try to convert the \302 and \247 to/from bytes by using `read'
> and `prin1' (since Emacs also uses such a notation for its own Elisp
> strings).  As for converting those bytes to/from chars, just use
> (en|de)code-coding-string.

Thanks! The funny thing is that I am trying to make emacs interact
with the program djvused that uses a rather lisp-like structure for
its input and output. So using `read' and `prin1' is anyway a
natural way to go.

Once my code is a bit more mature, I'll post it on
gnu-emacs-sources. Maybe it'll be helpful for others, too.

Roland