CVSROOT: /web/grep Module name: grep Changes by: Karl Berry <karl> 09/05/24 18:43:01
Index: manual/html_node/Back_002dreferences-and-Subexpressions.html =================================================================== RCS file: manual/html_node/Back_002dreferences-and-Subexpressions.html diff -N manual/html_node/Back_002dreferences-and-Subexpressions.html --- /dev/null 1 Jan 1970 00:00:00 -0000 +++ manual/html_node/Back_002dreferences-and-Subexpressions.html 24 May 2009 18:42:58 -0000 1.1 @@ -0,0 +1,65 @@ +<html lang="en"> +<head> +<title>Back-references and Subexpressions - GNU Grep 2.5.4</title> +<meta http-equiv="Content-Type" content="text/html"> +<meta name="description" content="GNU Grep 2.5.4"> +<meta name="generator" content="makeinfo 4.13"> +<link title="Top" rel="start" href="index.html#Top"> +<link rel="up" href="Regular-Expressions.html#Regular-Expressions" title="Regular Expressions"> +<link rel="prev" href="Anchoring.html#Anchoring" title="Anchoring"> +<link rel="next" href="Basic-vs-Extended.html#Basic-vs-Extended" title="Basic vs Extended"> +<link href="http://www.gnu.org/software/texinfo/"; rel="generator-home" title="Texinfo Homepage"> +<!-- +This manual is for `grep', a pattern matching engine. + +Copyright (C) 1999, 2000, 2001, 2002, 2005, 2008, 2009 Free +Software Foundation, Inc. + + Permission is granted to copy, distribute and/or modify this + document under the terms of the GNU Free Documentation License, + Version 1.3 or any later version published by the Free Software + Foundation; with no 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''. + --> +<meta http-equiv="Content-Style-Type" content="text/css"> +<style type="text/css"><!-- + pre.display { font-family:inherit } + pre.format { font-family:inherit } + pre.smalldisplay { font-family:inherit; font-size:smaller } + pre.smallformat { font-family:inherit; font-size:smaller } + pre.smallexample { font-size:smaller } + pre.smalllisp { font-size:smaller } + span.sc { font-variant:small-caps } + span.roman { font-family:serif; font-weight:normal; } + span.sansserif { font-family:sans-serif; font-weight:normal; } +--></style> +</head> +<body> +<div class="node"> +<a name="Back-references-and-Subexpressions"></a> +<a name="Back_002dreferences-and-Subexpressions"></a> +<p> +Next: <a rel="next" accesskey="n" href="Basic-vs-Extended.html#Basic-vs-Extended">Basic vs Extended</a>, +Previous: <a rel="previous" accesskey="p" href="Anchoring.html#Anchoring">Anchoring</a>, +Up: <a rel="up" accesskey="u" href="Regular-Expressions.html#Regular-Expressions">Regular Expressions</a> +<hr> +</div> + +<h3 class="section">3.5 Back-references and Subexpressions</h3> + +<p><a name="index-subexpression-237"></a><a name="index-back_002dreference-238"></a> +The back-reference ‘<samp><span class="samp">\</span><var>n</var></samp>’, where <var>n</var> is a single digit, matches +the substring previously matched by the <var>n</var>th parenthesized subexpression +of the regular expression. +For example, ‘<samp><span class="samp">(a)\1</span></samp>’ matches ‘<samp><span class="samp">aa</span></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><span class="samp">a(.)|b\1</span></samp>’ +will not match ‘<samp><span class="samp">ba</span></samp>’. +When multiple regular expressions are given with +‘<samp><span class="samp">-e</span></samp>’ or from a file (‘<samp><span class="samp">-f file</span></samp>’), +back-references are local to each expression. + + </body></html> +
