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Changes to grep/manual/html_node/Usage.html,v
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From: |
Jim Meyering |
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Subject: |
Changes to grep/manual/html_node/Usage.html,v |
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Date: |
Thu, 2 Jan 2020 18:18:46 -0500 (EST) |
CVSROOT: /webcvs/grep
Module name: grep
Changes by: Jim Meyering <meyering> 20/01/02 18:18:45
Index: html_node/Usage.html
===================================================================
RCS file: /webcvs/grep/grep/manual/html_node/Usage.html,v
retrieving revision 1.29
retrieving revision 1.30
diff -u -b -r1.29 -r1.30
--- html_node/Usage.html 30 Dec 2018 06:24:22 -0000 1.29
+++ html_node/Usage.html 2 Jan 2020 23:18:44 -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>Usage (GNU Grep 3.3)</title>
+<title>Usage (GNU Grep 3.4)</title>
-<meta name="description" content="Usage (GNU Grep 3.3)">
-<meta name="keywords" content="Usage (GNU Grep 3.3)">
+<meta name="description" content="Usage (GNU Grep 3.4)">
+<meta name="keywords" content="Usage (GNU Grep 3.4)">
<meta name="resource-type" content="document">
<meta name="distribution" content="global">
<meta name="Generator" content="makeinfo">
@@ -83,7 +83,27 @@
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.html#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.html#Invoking">Invoking</a>, for more details about
how to invoke <code>grep</code>.
</p>
<a name="index-using-grep_002c-Q_0026A"></a>
@@ -94,10 +114,10 @@
<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?
@@ -109,42 +129,51 @@
<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;
@@ -154,7 +183,7 @@
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
@@ -163,7 +192,7 @@
</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.
@@ -237,7 +266,7 @@
<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
@@ -252,30 +281,6 @@
<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">
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