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Changes to grep/manual/html_node/Back_002dreferences-and-Subexpressions.
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From: |
Jim Meyering |
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Subject: |
Changes to grep/manual/html_node/Back_002dreferences-and-Subexpressions.html, v |
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Date: |
Sat, 14 Aug 2021 16:46:42 -0400 (EDT) |
CVSROOT: /webcvs/grep
Module name: grep
Changes by: Jim Meyering <meyering> 21/08/14 16:46:41
Index: html_node/Back_002dreferences-and-Subexpressions.html
===================================================================
RCS file:
/webcvs/grep/grep/manual/html_node/Back_002dreferences-and-Subexpressions.html,v
retrieving revision 1.31
retrieving revision 1.32
diff -u -b -r1.31 -r1.32
--- html_node/Back_002dreferences-and-Subexpressions.html 28 Sep 2020
03:36:49 -0000 1.31
+++ html_node/Back_002dreferences-and-Subexpressions.html 14 Aug 2021
20:46:40 -0000 1.32
@@ -1,8 +1,11 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd";>
<html>
+<!-- Created by GNU Texinfo 6.8, https://www.gnu.org/software/texinfo/ -->
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<!-- This manual is for grep, a pattern matching engine.
-Copyright (C) 1999-2002, 2005, 2008-2020 Free Software Foundation,
+Copyright (C) 1999-2002, 2005, 2008-2021 Free Software Foundation,
Inc.
Permission is granted to copy, distribute and/or modify this document
@@ -11,80 +14,74 @@
Invariant Sections, with no Front-Cover Texts, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
"GNU Free Documentation License". -->
-<!-- Created by GNU Texinfo 6.5, http://www.gnu.org/software/texinfo/ -->
-<head>
-<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
-<title>Back-references and Subexpressions (GNU Grep 3.5)</title>
+<title>Back-references and Subexpressions (GNU Grep 3.7)</title>
-<meta name="description" content="Back-references and Subexpressions (GNU Grep
3.5)">
-<meta name="keywords" content="Back-references and Subexpressions (GNU Grep
3.5)">
+<meta name="description" content="Back-references and Subexpressions (GNU Grep
3.7)">
+<meta name="keywords" content="Back-references and Subexpressions (GNU Grep
3.7)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
-<link href="index.html#Top" rel="start" title="Top">
-<link href="Index.html#Index" rel="index" title="Index">
+<meta name="viewport" content="width=device-width,initial-scale=1">
+
+<link href="index.html" rel="start" title="Top">
+<link href="Index.html" rel="index" title="Index">
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
-<link href="Regular-Expressions.html#Regular-Expressions" rel="up"
title="Regular Expressions">
-<link href="Basic-vs-Extended.html#Basic-vs-Extended" rel="next" title="Basic
vs Extended">
-<link href="Anchoring.html#Anchoring" rel="prev" title="Anchoring">
+<link href="Regular-Expressions.html" rel="up" title="Regular Expressions">
+<link href="Basic-vs-Extended.html" rel="next" title="Basic vs Extended">
+<link href="Anchoring.html" rel="prev" title="Anchoring">
<style type="text/css">
<!--
+a.copiable-anchor {visibility: hidden; text-decoration: none; line-height: 0em}
a.summary-letter {text-decoration: none}
blockquote.indentedblock {margin-right: 0em}
-blockquote.smallindentedblock {margin-right: 0em; font-size: smaller}
-blockquote.smallquotation {font-size: smaller}
div.display {margin-left: 3.2em}
div.example {margin-left: 3.2em}
-div.lisp {margin-left: 3.2em}
-div.smalldisplay {margin-left: 3.2em}
-div.smallexample {margin-left: 3.2em}
-div.smalllisp {margin-left: 3.2em}
kbd {font-style: oblique}
pre.display {font-family: inherit}
pre.format {font-family: inherit}
pre.menu-comment {font-family: serif}
pre.menu-preformatted {font-family: serif}
-pre.smalldisplay {font-family: inherit; font-size: smaller}
-pre.smallexample {font-size: smaller}
-pre.smallformat {font-family: inherit; font-size: smaller}
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span.nolinebreak {white-space: nowrap}
span.roman {font-family: initial; font-weight: normal}
span.sansserif {font-family: sans-serif; font-weight: normal}
+span:hover a.copiable-anchor {visibility: visible}
ul.no-bullet {list-style: none}
-->
</style>
-<link rel="stylesheet" type="text/css" href="/software/gnulib/manual.css">
+<link rel="stylesheet" type="text/css"
href="https://www.gnu.org/software/gnulib/manual.css";>
</head>
<body lang="en">
-<a name="Back_002dreferences-and-Subexpressions"></a>
+<div class="section" id="Back_002dreferences-and-Subexpressions">
<div class="header">
<p>
-Next: <a href="Basic-vs-Extended.html#Basic-vs-Extended" accesskey="n"
rel="next">Basic vs Extended</a>, Previous: <a href="Anchoring.html#Anchoring"
accesskey="p" rel="prev">Anchoring</a>, Up: <a
href="Regular-Expressions.html#Regular-Expressions" accesskey="u"
rel="up">Regular Expressions</a> [<a href="index.html#SEC_Contents"
title="Table of contents" rel="contents">Contents</a>][<a
href="Index.html#Index" title="Index" rel="index">Index</a>]</p>
+Next: <a href="Basic-vs-Extended.html" accesskey="n" rel="next">Basic vs
Extended Regular Expressions</a>, Previous: <a href="Anchoring.html"
accesskey="p" rel="prev">Anchoring</a>, Up: <a href="Regular-Expressions.html"
accesskey="u" rel="up">Regular Expressions</a> [<a
href="index.html#SEC_Contents" title="Table of contents"
rel="contents">Contents</a>][<a href="Index.html" title="Index"
rel="index">Index</a>]</p>
</div>
<hr>
-<a name="Back_002dreferences-and-Subexpressions-1"></a>
-<h3 class="section">3.5 Back-references and Subexpressions</h3>
-<a name="index-subexpression"></a>
-<a name="index-back_002dreference"></a>
+<span id="Back_002dreferences-and-Subexpressions-1"></span><h3
class="section">3.5 Back-references and Subexpressions</h3>
+<span id="index-subexpression"></span>
+<span id="index-back_002dreference"></span>
-<p>The back-reference ‘<samp>\<var>n</var></samp>’, where
<var>n</var> is a single digit, matches
+<p>The back-reference ‘<samp>\<var>n</var></samp>’,
+where <var>n</var> is a single nonzero digit, matches
the substring previously matched by the <var>n</var>th parenthesized
subexpression
of the regular expression.
For example, ‘<samp>(a)\1</samp>’ matches
‘<samp>aa</samp>’.
-When used with alternation, if the group does not participate in the match then
-the back-reference makes the whole match fail.
-For example, ‘<samp>a(.)|b\1</samp>’
-will not match ‘<samp>ba</samp>’.
+If the parenthesized subexpression does not participate in the match,
+the back-reference makes the whole match fail;
+for example, ‘<samp>(a)*\1</samp>’ fails to match
‘<samp>a</samp>’.
+If the parenthesized subexpression matches more than one substring,
+the back-reference refers to the last matched substring;
+for example, ‘<samp>^(ab*)*\1$</samp>’ matches
‘<samp>ababbabb</samp>’ but not ‘<samp>ababbab</samp>’.
When multiple regular expressions are given with
<samp>-e</samp> or from a file (‘<samp>-f <var>file</var></samp>’),
back-references are local to each expression.
</p>
-<p>See <a href="Known-Bugs.html#Known-Bugs">Known Bugs</a>, for some known
problems with back-references.
+<p>See <a href="Known-Bugs.html">Known Bugs</a>, for some known problems with
back-references.
</p>
+</div>
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