From mboxrd@z Thu Jan 1 00:00:00 1970 Path: news.gmane.io!.POSTED.blaine.gmane.org!not-for-mail From: Stefan Monnier via Users list for the GNU Emacs text editor Newsgroups: gmane.emacs.help Subject: Re: Regular expressions and user-escaped characters Date: Tue, 03 Dec 2024 09:01:01 -0500 Message-ID: References: <87plm9g2rm.fsf@librehacker.com> Reply-To: Stefan Monnier Mime-Version: 1.0 Content-Type: text/plain Injection-Info: ciao.gmane.io; posting-host="blaine.gmane.org:116.202.254.214"; logging-data="16896"; mail-complaints-to="usenet@ciao.gmane.io" User-Agent: Gnus/5.13 (Gnus v5.13) To: help-gnu-emacs@gnu.org Cancel-Lock: sha1:4GjSpIms+qkFkjbQLxWTUoDJ19U= Original-X-From: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Tue Dec 03 15:01:52 2024 Return-path: Envelope-to: geh-help-gnu-emacs@m.gmane-mx.org Original-Received: from lists.gnu.org ([209.51.188.17]) by ciao.gmane.io with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1tITTM-0004JP-C2 for geh-help-gnu-emacs@m.gmane-mx.org; Tue, 03 Dec 2024 15:01:52 +0100 Original-Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1tITSl-0006bq-Eg; Tue, 03 Dec 2024 09:01:16 -0500 Original-Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tITSj-0006bW-IO for help-gnu-emacs@gnu.org; Tue, 03 Dec 2024 09:01:13 -0500 Original-Received: from ciao.gmane.io ([116.202.254.214]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1tITSg-0004ET-My for help-gnu-emacs@gnu.org; Tue, 03 Dec 2024 09:01:13 -0500 Original-Received: from list by ciao.gmane.io with local (Exim 4.92) (envelope-from ) id 1tITSe-0003Qs-RO for help-gnu-emacs@gnu.org; Tue, 03 Dec 2024 15:01:08 +0100 X-Injected-Via-Gmane: http://gmane.org/ Received-SPF: pass client-ip=116.202.254.214; envelope-from=geh-help-gnu-emacs@m.gmane-mx.org; helo=ciao.gmane.io X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, HEADER_FROM_DIFFERENT_DOMAINS=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: help-gnu-emacs@gnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Users list for the GNU Emacs text editor List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Original-Sender: help-gnu-emacs-bounces+geh-help-gnu-emacs=m.gmane-mx.org@gnu.org Xref: news.gmane.io gmane.emacs.help:148533 Archived-At: > Hi, what do you do in a regular expression if you want to match a character, > but not a the same character that has been escaped by the user. E.g., if > I want my regular expression to look for ?\[ (ASCII 91), matching string "[" > and "a[a" but not string "\\[" or "a\\[a", if you follow me. Is this > possible with just a regular expression? The "usual" way we do that is with the godawful: "\\(?:^\\|[^\\]\\(?:\\\\\\\\\\)*\\)\\[" This is careful to match the [ if it's preceded by an even number of backslashes. But beware that it makes more than the actual [, so if you start the search from a point that's looking at a [, it won't find it (except if it's at the beginning of the line). > If not, what is a good workaround? Just use a regexp which matches all [ (regardless of any previous backslashes) and then check afterwards, in ELisp, whether it's preceded by an odd number of backslashes, e.g. with something like (save-excursion (goto-char ) (zerop (% (skip-chars-backward "\\") 2))) - Stefan