From: Luc Teirlinck <teirllm@dms.auburn.edu>
Cc: rudalics@gmx.at, emacs-devel@gnu.org, schwab@suse.de
Subject: Re: Unquoted special characters in regexps
Date: Mon, 27 Feb 2006 18:30:13 -0600 (CST) [thread overview]
Message-ID: <200602280030.k1S0UDE07149@raven.dms.auburn.edu> (raw)
In-Reply-To: <E1FDneo-00050N-Nn@fencepost.gnu.org> (message from Richard Stallman on Mon, 27 Feb 2006 14:03:42 -0500)
None of the messages I sent on this (or on anything else) in the last
few days made it to emacs-devel, although all other people's
responses did, be it after some delay. I just got messages saying
that local delivery failed. So I will have to repeat some things that
I already said before.
Richard Stallman wrote:
However, that doesn't necessarily mean the manual is wrong.
There is more than one way to understand the word "special".
At the most literal level, ] is not special; if you write it
without \\, the regexp compiler won't misunderstand it.
`]', like `-' are only special in the context of a character
alternative, that is if, before you type them, you are in a character
alternative. By contrast, `[' and all other special characters
(except `^') are only special outside that context.
All characters that are special outside character alternatives are
never special if you precede them with a backslash. This is true even
for `^'. This is why it is good to precede them with a backslash even
if they are not special. That way, the reader can see that they are
not special, without studying the regexp.
On the other hand, a backslash, _never_ eliminates the special meaning
of a `]' or `-' with a special meaning.
There are two questions here. Whether a `]' outside a character
alternative should be quoted or not and whether any changes to the
Elisp manual are required. In this posting, I will only discuss the
first.
First of all, there are (surprisingly) many occurrences of "\\]" in
the Emacs source, where the `]' _is_ special and closes a character
alternative that contains a slash. Reportedly quoting a `]' with a
backslash _inside_ a character alternative works in some other regexp
implementations such as AWK. So if I see "\\]" I have to worry about
three possibilities: it might deliberately close a character
alternative which includes a slash, it might do so by accident because
the author tried to quote a `]' inside a character alternative (and
hence the regexp is buggy), or it might be a deliberately quoted `]'
outside a character alternative.
If I see `]' without preceding "\\", I only have to worry about
whether or not it closes a character alternative, and not about the
third possibility of a bug.
In summary I believe that quoting a `]' outside a character
alternative only adds clutter and a third possibility to worry about.
There are places in the Emacs code that quote a `]' outside a
character alternative. Even if we decide that this is undesirable, I
do not fancy finding and changing them all. But we could change the
behavior of `regexp-quote' and `regexp-opt' which currently quote
such `]'. That could be done with the following trivial patch, which
I could install if that is what we decide to do:
===File ~/search.c-diff=====================================
*** search.c 06 Feb 2006 16:02:24 -0600 1.206
--- search.c 27 Feb 2006 00:16:42 -0600
***************
*** 3066,3072 ****
for (; in != end; in++)
{
! if (*in == '[' || *in == ']'
|| *in == '*' || *in == '.' || *in == '\\'
|| *in == '?' || *in == '+'
|| *in == '^' || *in == '$')
--- 3066,3072 ----
for (; in != end; in++)
{
! if (*in == '['
|| *in == '*' || *in == '.' || *in == '\\'
|| *in == '?' || *in == '+'
|| *in == '^' || *in == '$')
============================================================
next prev parent reply other threads:[~2006-02-28 0:30 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-02-25 17:23 Unquoted special characters in regexps martin rudalics
2006-02-25 18:42 ` Andreas Schwab
2006-02-25 19:18 ` martin rudalics
2006-02-25 19:31 ` Andreas Schwab
2006-02-25 20:18 ` martin rudalics
2006-02-25 22:09 ` Andreas Schwab
2006-02-26 11:32 ` martin rudalics
2006-02-26 11:50 ` Andreas Schwab
2006-02-26 13:28 ` martin rudalics
2006-02-25 22:13 ` Luc Teirlinck
2006-02-26 13:13 ` martin rudalics
2006-02-26 13:50 ` Andreas Schwab
2006-02-26 16:41 ` Luc Teirlinck
2006-02-26 17:53 ` martin rudalics
2006-02-26 18:22 ` Luc Teirlinck
2006-02-26 19:26 ` martin rudalics
2006-02-26 17:10 ` martin rudalics
2006-02-26 17:42 ` Luc Teirlinck
2006-02-26 19:06 ` martin rudalics
2006-02-26 17:56 ` Andreas Schwab
2006-02-26 19:08 ` martin rudalics
2006-02-27 19:03 ` Richard Stallman
2006-02-27 19:36 ` Andreas Schwab
2006-02-27 20:03 ` martin rudalics
2006-02-27 20:32 ` Andreas Schwab
2006-02-27 21:43 ` martin rudalics
2006-02-27 22:11 ` Andreas Schwab
2006-02-28 6:19 ` Richard Stallman
2006-02-28 10:28 ` martin rudalics
2006-02-28 0:30 ` Luc Teirlinck [this message]
2006-02-28 10:27 ` martin rudalics
2006-02-28 22:57 ` Luc Teirlinck
2006-03-01 13:00 ` martin rudalics
2006-03-01 17:54 ` Richard Stallman
2006-03-02 4:06 ` Luc Teirlinck
2006-03-02 19:43 ` Richard Stallman
2006-03-02 4:54 ` Luc Teirlinck
2006-03-02 18:40 ` martin rudalics
2006-03-02 23:26 ` Luc Teirlinck
2006-03-03 7:42 ` martin rudalics
2006-03-03 13:51 ` Luc Teirlinck
2006-03-03 14:09 ` Luc Teirlinck
2006-03-03 18:52 ` martin rudalics
2006-03-03 22:41 ` Luc Teirlinck
2006-03-03 23:00 ` Luc Teirlinck
2006-03-03 10:25 ` Richard Stallman
2006-03-03 15:20 ` martin rudalics
2006-03-04 13:37 ` Richard Stallman
2006-03-04 14:40 ` martin rudalics
2006-03-06 0:48 ` Richard Stallman
2006-03-03 10:25 ` Richard Stallman
2006-03-03 15:51 ` martin rudalics
2006-03-03 23:48 ` Luc Teirlinck
2006-03-04 9:58 ` martin rudalics
2006-03-04 23:16 ` Luc Teirlinck
2006-03-05 2:54 ` Luc Teirlinck
2006-03-06 0:49 ` Richard Stallman
2006-02-28 0:44 ` Luc Teirlinck
2006-03-04 21:07 ` Thien-Thi Nguyen
2006-03-05 3:37 ` Luc Teirlinck
2006-03-05 11:10 ` martin rudalics
2006-03-05 15:32 ` Luc Teirlinck
2006-03-06 7:41 ` martin rudalics
2006-03-05 17:04 ` Luc Teirlinck
2006-03-05 11:54 ` martin rudalics
2006-03-05 15:35 ` Andreas Schwab
2006-03-06 8:19 ` martin rudalics
2006-03-05 18:36 ` Luc Teirlinck
2006-03-05 19:14 ` Luc Teirlinck
2006-03-06 8:17 ` martin rudalics
2006-02-28 0:59 ` Luc Teirlinck
2006-03-06 12:52 ` Richard Stallman
2006-03-07 5:52 ` Luc Teirlinck
2006-03-07 8:53 ` martin rudalics
2006-02-25 22:34 ` Luc Teirlinck
2006-02-25 22:59 ` Andreas Schwab
2006-02-26 13:20 ` martin rudalics
2006-02-26 16:53 ` Luc Teirlinck
2006-02-26 18:01 ` martin rudalics
2006-02-26 17:19 ` Luc Teirlinck
2006-02-26 18:13 ` martin rudalics
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