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Changes to grep/manual/grep.html,v
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From: |
Jim Meyering |
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Subject: |
Changes to grep/manual/grep.html,v |
|
Date: |
Thu, 2 Jan 2020 18:18:45 -0500 (EST) |
CVSROOT: /webcvs/grep
Module name: grep
Changes by: Jim Meyering <meyering> 20/01/02 18:18:45
Index: grep.html
===================================================================
RCS file: /webcvs/grep/grep/manual/grep.html,v
retrieving revision 1.29
retrieving revision 1.30
diff -u -b -r1.29 -r1.30
--- grep.html 30 Dec 2018 06:24:21 -0000 1.29
+++ grep.html 2 Jan 2020 23:18:43 -0000 1.30
@@ -2,7 +2,7 @@
<html>
<!-- This manual is for grep, a pattern matching engine.
-Copyright (C) 1999-2002, 2005, 2008-2018 Free Software Foundation,
+Copyright (C) 1999-2002, 2005, 2008-2020 Free Software Foundation,
Inc.
Permission is granted to copy, distribute and/or modify this document
@@ -14,10 +14,10 @@
<!-- 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>GNU Grep 3.3</title>
+<title>GNU Grep 3.4</title>
-<meta name="description" content="GNU Grep 3.3">
-<meta name="keywords" content="GNU Grep 3.3">
+<meta name="description" content="GNU Grep 3.4">
+<meta name="keywords" content="GNU Grep 3.4">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
@@ -58,7 +58,7 @@
</head>
<body lang="en">
-<h1 class="settitle" align="center">GNU Grep 3.3</h1>
+<h1 class="settitle" align="center">GNU Grep 3.4</h1>
@@ -101,7 +101,7 @@
<li><a name="toc-Performance-1" href="#Performance">5 Performance</a></li>
<li><a name="toc-Reporting-bugs" href="#Reporting-Bugs">6 Reporting bugs</a>
<ul class="no-bullet">
- <li><a name="toc-Known-Bugs" href="#Known-Bugs">6.1 Known Bugs</a></li>
+ <li><a name="toc-Known-Bugs-1" href="#Known-Bugs">6.1 Known Bugs</a></li>
</ul></li>
<li><a name="toc-Copying-1" href="#Copying">7 Copying</a>
<ul class="no-bullet">
@@ -123,11 +123,11 @@
<p><code>grep</code> prints lines that contain a match for one or more
patterns.
</p>
-<p>This manual is for version 3.3 of GNU Grep.
+<p>This manual is for version 3.4 of GNU Grep.
</p>
<p>This manual is for <code>grep</code>, a pattern matching engine.
</p>
-<p>Copyright © 1999-2002, 2005, 2008-2018 Free Software Foundation,
+<p>Copyright © 1999–2002, 2005, 2008–2020 Free Software
Foundation,
Inc.
</p>
<blockquote>
@@ -201,12 +201,12 @@
<pre class="example">grep [<var>option</var>...] [<var>patterns</var>]
[<var>file</var>...]
</pre></div>
-
<p>There can be zero or more <var>option</var> arguments, and zero or more
<var>file</var> arguments. The <var>patterns</var> argument contains one or
more patterns separated by newlines, and is omitted when patterns are
given via the ‘<samp>-e <var>patterns</var></samp>’ or
‘<samp>-f <var>file</var></samp>’
-options.
+options. Typically <var>patterns</var> should be quoted when
+<code>grep</code> is used in a shell command.
</p>
<table class="menu" border="0" cellspacing="0">
<tr><td align="left" valign="top">• <a href="#Command_002dline-Options"
accesskey="1">Command-line Options</a>:</td><td> </td><td
align="left" valign="top">Short and long names, grouped by category.
@@ -307,6 +307,8 @@
<var>patterns</var> separate each pattern from the next.
If this option is used multiple times or is combined with the
<samp>-f</samp> (<samp>--file</samp>) option, search for all patterns given.
+Typically <var>patterns</var> should be quoted when <code>grep</code> is used
+in a shell command.
(<samp>-e</samp> is specified by POSIX.)
</p>
</dd>
@@ -329,7 +331,8 @@
<a name="index-_002dy"></a>
<a name="index-_002d_002dignore_002dcase"></a>
<a name="index-case-insensitive-search"></a>
-<p>Ignore case distinctions, so that characters that differ only in case
+<p>Ignore case distinctions in patterns and input data,
+so that characters that differ only in case
match each other. Although this is straightforward when letters
differ in case only via lowercase-uppercase pairs, the behavior is
unspecified in other situations. For example, uppercase “S” has an
@@ -346,6 +349,14 @@
(<samp>-i</samp> is specified by POSIX.)
</p>
</dd>
+<dt><samp>--no-ignore-case</samp></dt>
+<dd><a name="index-_002d_002dno_002dignore_002dcase"></a>
+<p>Do not ignore case distinctions in patterns and input data. This is
+the default. This option is useful for passing to shell scripts that
+already use <samp>-i</samp>, in order to cancel its effects because the
+two options override each other.
+</p>
+</dd>
<dt><samp>-v</samp></dt>
<dt><samp>--invert-match</samp></dt>
<dd><a name="index-_002dv"></a>
@@ -472,7 +483,7 @@
For example, the following shell script makes use of it:
</p>
<div class="example">
-<pre class="example">while grep -m 1 PATTERN
+<pre class="example">while grep -m 1 'PATTERN'
do
echo xxxx
done < FILE
@@ -484,7 +495,7 @@
<div class="example">
<pre class="example"># This probably will not work.
cat FILE |
-while grep -m 1 PATTERN
+while grep -m 1 'PATTERN'
do
echo xxxx
done
@@ -594,12 +605,12 @@
<dd><a name="index-_002d_002dlabel"></a>
<a name="index-changing-name-of-standard-input"></a>
<p>Display input actually coming from standard input
-as input coming from file <var>LABEL</var>. This is
-especially useful when implementing tools like
-<code>zgrep</code>; e.g.:
+as input coming from file <var>LABEL</var>.
+This can be useful for commands that transform a file’s contents
+before searching; e.g.:
</p>
<div class="example">
-<pre class="example">gzip -cd foo.gz | grep --label=foo -H something
+<pre class="example">gzip -cd foo.gz | grep --label=foo -H 'some pattern'
</pre></div>
</dd>
@@ -840,10 +851,11 @@
<a name="index-searching-directory-trees"></a>
<p>Skip any command-line file with a name suffix that matches the pattern
<var>glob</var>, using wildcard matching; a name suffix is either the whole
-name, or any suffix starting after a ‘<samp>/</samp>’ and before a
-non-‘<samp>/</samp>’. When searching recursively, skip any
subfile whose base
+name, or a trailing part that starts with a non-slash character
+immediately after a slash (‘<samp>/</samp>’) in the name.
+When searching recursively, skip any subfile whose base
name matches <var>glob</var>; the base name is the part after the last
-‘<samp>/</samp>’. A pattern can use
+slash. A pattern can use
‘<samp>*</samp>’, ‘<samp>?</samp>’, and
‘<samp>[</samp>’...‘<samp>]</samp>’ as wildcards,
and <code>\</code> to quote a wildcard or backslash character literally.
</p>
@@ -1809,6 +1821,8 @@
<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">Known Bugs</a>, for some known problems with
back-references.
+</p>
<hr>
<a name="Basic-vs-Extended"></a>
<div class="header">
@@ -1863,7 +1877,27 @@
The <samp>-i</samp> option causes <code>grep</code>
to ignore case, causing it to match the line ‘<samp>Hello,
world!</samp>’, which
it would not otherwise match.
-See <a href="#Invoking">Invoking</a>, for more details about
+</p>
+<p>Here is a more complex example session,
+showing the location and contents of any line
+containing ‘<samp>f</samp>’ and ending in
‘<samp>.c</samp>’,
+within all files in the current directory whose names
+contain ‘<samp>g</samp>’ and end in ‘<samp>.h</samp>’.
+The <samp>-n</samp> option outputs line numbers, the <samp>--</samp> argument
+treats any later arguments starting with ‘<samp>-</samp>’ as file
names not
+options, and the empty file <samp>/dev/null</samp> causes file names to be
output
+even if only one file name happens to be of the form
‘<samp>*g*.h</samp>’.
+</p>
+<div class="example">
+<pre class="example">$ <kbd>grep -n -- 'f.*\.c$' *g*.h /dev/null</kbd>
+argmatch.h:1:/* definitions and prototypes for argmatch.c
+</pre></div>
+
+<p>The only line that contains a match is line 1 of <samp>argmatch.h</samp>.
+Note that the regular expression syntax used in the pattern differs
+from the globbing syntax that the shell uses to match file names.
+</p>
+<p>See <a href="#Invoking">Invoking</a>, for more details about
how to invoke <code>grep</code>.
</p>
<a name="index-using-grep_002c-Q_0026A"></a>
@@ -1874,10 +1908,10 @@
<li> How can I list just the names of matching files?
<div class="example">
-<pre class="example">grep -l 'main' *.c
+<pre class="example">grep -l 'main' test-*.c
</pre></div>
-<p>lists the names of all C files in the current directory whose contents
+<p>lists names of ‘<samp>test-*.c</samp>’ files in the current
directory whose contents
mention ‘<samp>main</samp>’.
</p>
</li><li> How do I search directories recursively?
@@ -1889,42 +1923,51 @@
<p>searches for ‘<samp>hello</samp>’ in all files
under the <samp>/home/gigi</samp> directory.
For more control over which files are searched,
-use <code>find</code>, <code>grep</code>, and <code>xargs</code>.
+use <code>find</code> and <code>grep</code>.
For example, the following command searches only C files:
</p>
<div class="example">
-<pre class="example">find /home/gigi -name '*.c' -print0 | xargs -0r grep -H
'hello'
+<pre class="example">find /home/gigi -name '*.c' ! -type d \
+ -exec grep -H 'hello' '{}' +
</pre></div>
<p>This differs from the command:
</p>
<div class="example">
-<pre class="example">grep -H 'hello' *.c
+<pre class="example">grep -H 'hello' /home/gigi/*.c
</pre></div>
-<p>which merely looks for ‘<samp>hello</samp>’ in all files in the
current
-directory whose names end in ‘<samp>.c</samp>’.
-The ‘<samp>find ...</samp>’ command line above is more similar to
the command:
+<p>which merely looks for ‘<samp>hello</samp>’ in non-hidden C
files in
+<samp>/home/gigi</samp> whose names end in ‘<samp>.c</samp>’.
+The <code>find</code> command line above is more similar to the command:
</p>
<div class="example">
-<pre class="example">grep -rH --include='*.c' 'hello' /home/gigi
+<pre class="example">grep -r --include='*.c' 'hello' /home/gigi
</pre></div>
-</li><li> What if a pattern has a leading ‘<samp>-</samp>’?
+</li><li> What if a pattern or file has a leading ‘<samp>-</samp>’?
<div class="example">
-<pre class="example">grep -e '--cut here--' *
+<pre class="example">grep -- '--cut here--' *
</pre></div>
<p>searches for all lines matching ‘<samp>--cut here--</samp>’.
-Without <samp>-e</samp>,
+Without <samp>--</samp>,
<code>grep</code> would attempt to parse ‘<samp>--cut
here--</samp>’ as a list of
-options.
+options, and there would be similar problems with any file names
+beginning with ‘<samp>-</samp>’.
</p>
+<p>Alternatively, you can prevent misinterpretation of leading
‘<samp>-</samp>’
+by using <samp>-e</samp> for patterns and leading
‘<samp>./</samp>’ for files:
+</p>
+<div class="example">
+<pre class="example">grep -e '--cut here--' ./*
+</pre></div>
+
</li><li> Suppose I want to search for a whole word, not a part of a word?
<div class="example">
-<pre class="example">grep -w 'hello' *
+<pre class="example">grep -w 'hello' test*.log
</pre></div>
<p>searches only for instances of ‘<samp>hello</samp>’ that are
entire words;
@@ -1934,7 +1977,7 @@
For example:
</p>
<div class="example">
-<pre class="example">grep 'hello\>' *
+<pre class="example">grep 'hello\>' test*.log
</pre></div>
<p>searches only for words ending in ‘<samp>hello</samp>’, so it
matches the word
@@ -1943,7 +1986,7 @@
</li><li> How do I output context around the matching lines?
<div class="example">
-<pre class="example">grep -C 2 'hello' *
+<pre class="example">grep -C 2 'hello' test*.log
</pre></div>
<p>prints two lines of context around each matching line.
@@ -2017,7 +2060,7 @@
<p>The <code>grep</code> command searches for lines that contain strings
that match a pattern. Every line contains the empty string, so an
empty pattern causes <code>grep</code> to find a match on each line. It
-is not the only such pattern: ‘<samp>^</samp>’,
‘<samp>$</samp>’, ‘<samp>.*</samp>’, and many
+is not the only such pattern: ‘<samp>^</samp>’,
‘<samp>$</samp>’, and many
other patterns cause <code>grep</code> to match every line.
</p>
<p>To match empty lines, use the pattern ‘<samp>^$</samp>’. To
match blank
@@ -2032,30 +2075,6 @@
<pre class="example">cat /etc/passwd | grep 'alain' - /etc/motd
</pre></div>
-</li><li> <a name="index-palindromes"></a>
-How to express palindromes in a regular expression?
-
-<p>It can be done by using back-references;
-for example,
-a palindrome of 4 characters can be written with a BRE:
-</p>
-<div class="example">
-<pre class="example">grep -w -e '\(.\)\(.\).\2\1' file
-</pre></div>
-
-<p>It matches the word “radar” or “civic.”
-</p>
-<p>Guglielmo Bondioni proposed a single RE
-that finds all palindromes up to 19 characters long
-using 9 subexpressions<!-- /@w --> and 9 <span
class="nolinebreak">back-references</span><!-- /@w -->:
-</p>
-<div class="smallexample">
-<pre class="smallexample">grep -E -e
'^(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?).?\9\8\7\6\5\4\3\2\1$' file
-</pre></div>
-
-<p>Note this is done by using GNU ERE extensions;
-it might not be portable to other implementations of <code>grep</code>.
-</p>
</li><li> Why is this back-reference failing?
<div class="example">
@@ -2208,7 +2227,18 @@
If you find a bug not listed there, please email it to
<a href="mailto:address@hidden";>address@hidden</a> to create a new bug report.
</p>
+<table class="menu" border="0" cellspacing="0">
+<tr><td align="left" valign="top">• <a href="#Known-Bugs"
accesskey="1">Known Bugs</a>:</td><td> </td><td align="left"
valign="top">
+</td></tr>
+</table>
+
+<hr>
<a name="Known-Bugs"></a>
+<div class="header">
+<p>
+Up: <a href="#Reporting-Bugs" accesskey="u" rel="up">Reporting Bugs</a>
[<a href="#SEC_Contents" title="Table of contents"
rel="contents">Contents</a>][<a href="#Index" title="Index"
rel="index">Index</a>]</p>
+</div>
+<a name="Known-Bugs-1"></a>
<h3 class="section">6.1 Known Bugs</h3>
<a name="index-Bugs_002c-known"></a>
@@ -2218,7 +2248,17 @@
obscure regular expressions require exponential time and
space, and may cause <code>grep</code> to run out of memory.
</p>
-<p>Back-references are very slow, and may require exponential time.
+<p>Back-references can greatly slow down matching, as they can generate
+exponentially many matching possibilities that can consume both time
+and memory to explore. Also, the POSIX specification for
+back-references is at times unclear. Furthermore, many regular
+expression implementations have back-reference bugs that can cause
+programs to return incorrect answers or even crash, and fixing these
+bugs has often been low-priority—for example, as of 2019 the GNU C
+library bug database contained back-reference bugs 52, 10844, 11053,
+and 25322, with little sign of forthcoming fixes. Luckily,
+back-references are rarely useful and it should be little trouble to
+avoid them in practical applications.
</p>
<hr>
@@ -2852,6 +2892,7 @@
<tr><td></td><td valign="top"><a
href="#index-_002d_002dline_002dregexp"><code>--line-regexp</code></a>:</td><td> </td><td
valign="top"><a href="#Matching-Control">Matching Control</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-_002d_002dmax_002dcount"><code>--max-count</code></a>:</td><td> </td><td
valign="top"><a href="#General-Output-Control">General Output
Control</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-_002d_002dno_002dfilename"><code>--no-filename</code></a>:</td><td> </td><td
valign="top"><a href="#Output-Line-Prefix-Control">Output Line Prefix
Control</a></td></tr>
+<tr><td></td><td valign="top"><a
href="#index-_002d_002dno_002dignore_002dcase"><code>--no-ignore-case</code></a>:</td><td> </td><td
valign="top"><a href="#Matching-Control">Matching Control</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-_002d_002dno_002dmessages"><code>--no-messages</code></a>:</td><td> </td><td
valign="top"><a href="#General-Output-Control">General Output
Control</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-_002d_002dnull"><code>--null</code></a>:</td><td> </td><td
valign="top"><a href="#Output-Line-Prefix-Control">Output Line Prefix
Control</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-_002d_002dnull_002ddata"><code>--null-data</code></a>:</td><td> </td><td
valign="top"><a href="#Other-Options">Other Options</a></td></tr>
@@ -2943,7 +2984,7 @@
<tr><td></td><td valign="top"><a
href="#index-braces_002c-second-argument-omitted">braces, second argument
omitted</a>:</td><td> </td><td valign="top"><a
href="#Fundamental-Structure">Fundamental Structure</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-braces_002c-two-arguments">braces, two
arguments</a>:</td><td> </td><td valign="top"><a
href="#Fundamental-Structure">Fundamental Structure</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-bracket-expression">bracket
expression</a>:</td><td> </td><td valign="top"><a
href="#Character-Classes-and-Bracket-Expressions">Character Classes and Bracket
Expressions</a></td></tr>
-<tr><td></td><td valign="top"><a href="#index-Bugs_002c-known">Bugs,
known</a>:</td><td> </td><td valign="top"><a
href="#Reporting-Bugs">Reporting Bugs</a></td></tr>
+<tr><td></td><td valign="top"><a href="#index-Bugs_002c-known">Bugs,
known</a>:</td><td> </td><td valign="top"><a href="#Known-Bugs">Known
Bugs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-bugs_002c-reporting">bugs,
reporting</a>:</td><td> </td><td valign="top"><a
href="#Reporting-Bugs">Reporting Bugs</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-byte-offset">byte
offset</a>:</td><td> </td><td valign="top"><a
href="#Output-Line-Prefix-Control">Output Line Prefix Control</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
@@ -3069,7 +3110,6 @@
<tr><td></td><td valign="top"><a href="#index-option-delimiter">option
delimiter</a>:</td><td> </td><td valign="top"><a
href="#Other-Options">Other Options</a></td></tr>
<tr><td colspan="4"> <hr></td></tr>
<tr><th><a name="Index_cp_letter-P">P</a></th><td></td><td></td></tr>
-<tr><td></td><td valign="top"><a
href="#index-palindromes">palindromes</a>:</td><td> </td><td
valign="top"><a href="#Usage">Usage</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-patterns-from-file">patterns
from file</a>:</td><td> </td><td valign="top"><a
href="#Matching-Control">Matching Control</a></td></tr>
<tr><td></td><td valign="top"><a href="#index-patterns-option">patterns
option</a>:</td><td> </td><td valign="top"><a
href="#Matching-Control">Matching Control</a></td></tr>
<tr><td></td><td valign="top"><a
href="#index-performance">performance</a>:</td><td> </td><td
valign="top"><a href="#Performance">Performance</a></td></tr>
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