CVSROOT: /webcvs/grep Module name: grep Changes by: Jim Meyering <meyering> 21/08/14 16:46:41
Index: html_node/Basic-vs-Extended.html =================================================================== RCS file: /webcvs/grep/grep/manual/html_node/Basic-vs-Extended.html,v retrieving revision 1.31 retrieving revision 1.32 diff -u -b -r1.31 -r1.32 --- html_node/Basic-vs-Extended.html 28 Sep 2020 03:36:49 -0000 1.31 +++ html_node/Basic-vs-Extended.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. 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instead use the backslashed versions ‘<samp>\?</samp>’, ‘<samp>\+</samp>’, ‘<samp>\{</samp>’, -‘<samp>\|</samp>’, ‘<samp>\(</samp>’, and ‘<samp>\)</samp>’. +‘<samp>\|</samp>’, ‘<samp>\(</samp>’, and ‘<samp>\)</samp>’. Also, a backslash is needed +before an interval expression’s closing ‘<samp>}</samp>’, and an unmatched +<code>\)</code> is invalid. +</p> +<p>Portable scripts should avoid the following constructs, as +POSIX says they produce undefined results: </p> -<a name="index-interval-specifications"></a> -<p>Traditional <code>egrep</code> did not support the ‘<samp>{</samp>’ meta-character, -and some <code>egrep</code> implementations support ‘<samp>\{</samp>’ instead, so -portable scripts should avoid ‘<samp>{</samp>’ in ‘<samp>grep -E</samp>’ patterns and -should use ‘<samp>[{]</samp>’ to match a literal ‘<samp>{</samp>’. +<ul> +<li> Extended regular expressions that use back-references. +</li><li> Basic regular expressions that use ‘<samp>\?</samp>’, ‘<samp>\+</samp>’, or ‘<samp>\|</samp>’. +</li><li> Empty parenthesized regular expressions like ‘<samp>()</samp>’. +</li><li> Empty alternatives (as in, e.g, ‘<samp>a|</samp>’). +</li><li> Repetition operators that immediately follow empty expressions, +unescaped ‘<samp>$</samp>’, or other repetition operators. +</li><li> A backslash escaping an ordinary character (e.g., ‘<samp>\S</samp>’), +unless it is a back-reference. +</li><li> An unescaped ‘<samp>[</samp>’ that is not part of a bracket expression. +</li><li> In extended regular expressions, an unescaped ‘<samp>{</samp>’ that is not +part of an interval expression. +</li></ul> + +<span id="index-interval-expressions-1"></span> +<p>Traditional <code>egrep</code> did not support interval expressions and +some <code>egrep</code> implementations use ‘<samp>\{</samp>’ and ‘<samp>\}</samp>’ instead, so +portable scripts should avoid interval expressions in ‘<samp>grep -E</samp>’ patterns +and should use ‘<samp>[{]</samp>’ to match a literal ‘<samp>{</samp>’. </p> <p>GNU <code>grep -E</code> attempts to support traditional usage by assuming that ‘<samp>{</samp>’ is not special if it would be the start of an -invalid interval specification. +invalid interval expression. For example, the command ‘<samp>grep -E '{1'</samp>’ searches for the two-character string ‘<samp>{1</samp>’ instead of reporting a syntax error in the regular expression. POSIX allows this behavior as an extension, but portable scripts should avoid it. </p> +</div>
