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Re: Making re-search-forward search for \377

From: Tyler Spivey
Subject: Re: Making re-search-forward search for \377
Date: Sun, 02 Nov 2008 14:35:21 -0800
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux)

Xah <address@hidden> writes:

> Xah Lee wrote:
>> Xah<address@hidden> writes:
>> > what's the C-q 377 char?
>> > if i press Ctrl+q 377 Enter, i get this char: ÿ, which is LATIN SMALL
>> > LETTER Y WITH DIAERESIS (unicode U+00FF).
>> > Then if i do:
>> > (re-search-forward "ÿ")
> Tyler Spivey wrote:
>> I'm probably going to end up working with binary data in a temp
>> buffer. Doing more research, I want enable-multibyte-characters to be
>> off. Given that, if we go to *scratch*
>> and run M-X toggle-enable-multibyte-characters until that variable
>> becomes nil, doing C-Q 377 RET gives 0xff, which is what I want
>> (according to C-x =, C-u C-x = and M-x describe-char). Now to
>> match it, I try:
>> (re-search-forward "\xff") - no luck
I've done yet more digging, and it seems that I need to use
raw-text-unix encoding. I've sort of got this to work, and this next
example is more like what I'm doing; the smallest part that seems to
  (setq re1 "\377\371")
  (setq re2 "\\(\377\371\\)")
  (insert (decode-coding-string "line 1\nline 2\377\371" 'raw-text-unix)))

Evaluate that in an empty buffer, and then run M-: (re-search-forward re1) RET 
at the beginning of the text after the sexp.
Then try M-: (re-search-forward re2) RET from just after the sexp.
re1 matches fine, but re2 won't match. What am I missing here? I thought that 
putting parens around re1 to get re2 should
give me the same expression but with capturing. Here are details on my emacs 
GNU Emacs (x86_64-unknown-linux-gnu, GTK+ Version 2.14.4) of 
2008-11-01 on arch1
I tested this in 22.3, and it seems to work. In reading the NEWS file for 23,
I see changes in character set handling. What do I need to do to make re2 match 
what re1 does but with capturing? I realize
that in this case I can probably use (match-string 0), but the full RE that I'm 
going to eventually be matching on is this:
Any help would be appreciated.
- Tyler

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