From: martin rudalics <rudalics@gmx.at>
Cc: schwab@suse.de, rms@gnu.org, emacs-devel@gnu.org
Subject: Re: Unquoted special characters in regexps
Date: Wed, 01 Mar 2006 14:00:05 +0100 [thread overview]
Message-ID: <44059AD5.4030602@gmx.at> (raw)
In-Reply-To: <200602282257.k1SMvqU26046@raven.dms.auburn.edu>
> Martin Rudalics wrote:
>
> It would be strange to say, for example, that the double-quote
> opening an Elisp string is outside the context of the string and
> the double-quote that closes it inside.
>
> I do not see why you consider this strange. Quite to the contrary,
> this is exactly what allows one to determine whether a `"' opens or
> closes a string. `"" is special both inside and outside the context
> of a string. But its special meaning depends on that context.
> Outside the context of a string `"' starts a string, inside the
> context of a string, `"' ends a string. So an opening `"' is opening
> _because_ it occurs outside of a string context and the closing `"' is
> the closing one _because_ it occurs inside a string context.
>
> Note that the GNU regexp manual, node `(regex)List Operators' agrees
> with Andreas and me that `[' is special _outside_ a character alternative
> (by stating that it is ordinary inside one) and explicitly states that
> `]' has the special meaning of closing a character alternative
> _inside_ a character alternative. (Note that it refers to character
> alternatives as "lists".)
If you refer to section "3.6 List Operators ([ ... ] and [^ ... ])" of
the GNU regex manual I can exctract three relevant sentences:
"A matching list matches a single character represented by one of the
list items. You form a matching list by enclosing one or more items
within an open-matching-list operator (represented by `[') and a
close-list operator (represented by `]')."
If you deduce here that the "close-list operator" is part of the "items
within" you can deduce that the "open-matching-list" operator is part of
the "items within" as well.
"`]' ends the list if it's not the first list item. So, if you want to
make the `]' character a list item, you must put it first."
`]' is special inside a chararacter list - the "items within" mentioned
above - because it has to appear as the first element of that list.
"`-' represents the range operator (see section 3.6.2 The Range Operator
(-)) if it's not first or last in a list or the ending point of a range."
If `-' can be "last in a list" the close-list operator `]' cannot be
"last in that list". Ex falso sequitur quodlibet.
If anyone's interested in how other languages handle regexp brackets
see the list below:
Perl's metacharacters are:
{ } [ ] ( ) ^ $ . | * + ? \
Python metacharacters are:
. ^ $ * + ? { [ ] \ | ( )
PHP:
Outside square brackets, the meta-characters are as follows:
...
[ start character class definition
] end character class definition
...
XML:
A metacharacter is either ., \, ?, *, +, {, } (, ), [ or ].
Tcl:
A regular expression uses metacharacters (characters that assume special
meaning for matching other characters) such as *, [], $ and ..
...
A backslash (\) disables the special meaning of the following character,
so you could match the string [Hello] with the RE \[Hello\].
Java (http://java.sun.com/j2se/1.4.2/docs/api/java/util/regex/Pattern.html):
Perl is forgiving about malformed matching constructs, as in the
expression *a, as well as dangling brackets, as in the expression
abc], and treats them as literals.
Java also accepts dangling brackets but is strict about dangling
metacharacters like +, ? and *, and will throw a
PatternSyntaxException if it encounters them.
Hence all classic regexp languages do consider `]' special and do not
consider `-' special. The Java doc calls the `]' in `abc]' a dangling
bracket. The fact that languages "forgive" or "accept" such constructs
shouldn't cause anyone to promote such style.
next prev parent reply other threads:[~2006-03-01 13:00 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
2006-02-28 10:27 ` martin rudalics
2006-02-28 22:57 ` Luc Teirlinck
2006-03-01 13:00 ` martin rudalics [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://www.gnu.org/software/emacs/
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=44059AD5.4030602@gmx.at \
--to=rudalics@gmx.at \
--cc=emacs-devel@gnu.org \
--cc=rms@gnu.org \
--cc=schwab@suse.de \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.savannah.gnu.org/cgit/emacs.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).