CVSROOT: /web/grep Module name: grep Changes by: Karl Berry <karl> 09/05/24 18:43:01
Index: manual/html_node/Usage.html =================================================================== RCS file: manual/html_node/Usage.html diff -N manual/html_node/Usage.html --- /dev/null 1 Jan 1970 00:00:00 -0000 +++ manual/html_node/Usage.html 24 May 2009 18:43:00 -0000 1.1 @@ -0,0 +1,234 @@ +<html lang="en"> +<head> +<title>Usage - 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="prev" href="Regular-Expressions.html#Regular-Expressions" title="Regular Expressions"> +<link rel="next" href="Reporting-Bugs.html#Reporting-Bugs" title="Reporting Bugs"> +<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="Usage"></a> +<p> +Next: <a rel="next" accesskey="n" href="Reporting-Bugs.html#Reporting-Bugs">Reporting Bugs</a>, +Previous: <a rel="previous" accesskey="p" href="Regular-Expressions.html#Regular-Expressions">Regular Expressions</a>, +Up: <a rel="up" accesskey="u" href="index.html#Top">Top</a> +<hr> +</div> + +<h2 class="chapter">4 Usage</h2> + +<p><a name="index-usage_002c-examples-241"></a>Here is an example command that invokes <span class="sc">gnu</span> <samp><span class="command">grep</span></samp>: + +<pre class="example"> grep -i 'hello.*world' menu.h main.c +</pre> + <p class="noindent">This lists all lines in the files <samp><span class="file">menu.h</span></samp> and <samp><span class="file">main.c</span></samp> that +contain the string ‘<samp><span class="samp">hello</span></samp>’ followed by the string ‘<samp><span class="samp">world</span></samp>’; +this is because ‘<samp><span class="samp">.*</span></samp>’ matches zero or more characters within a line. +See <a href="Regular-Expressions.html#Regular-Expressions">Regular Expressions</a>. +The ‘<samp><span class="samp">-i</span></samp>’ option causes <samp><span class="command">grep</span></samp> +to ignore case, causing it to match the line ‘<samp><span class="samp">Hello, world!</span></samp>’, which +it would not otherwise match. +See <a href="Invoking.html#Invoking">Invoking</a>, for more details about +how to invoke <samp><span class="command">grep</span></samp>. + + <p><a name="index-using-_0040command_007bgrep_007d_002c-Q_0026A-242"></a><a name="index-FAQ-about-_0040command_007bgrep_007d-usage-243"></a>Here are some common questions and answers about <samp><span class="command">grep</span></samp> usage. + + <ol type=1 start=1> + + <li>How can I list just the names of matching files? + + <pre class="example"> grep -l 'main' *.c +</pre> + <p class="noindent">lists the names of all C files in the current directory whose contents +mention ‘<samp><span class="samp">main</span></samp>’. + + <li>How do I search directories recursively? + + <pre class="example"> grep -r 'hello' /home/gigi +</pre> + <p class="noindent">searches for ‘<samp><span class="samp">hello</span></samp>’ in all files +under the <samp><span class="file">/home/gigi</span></samp> directory. +For more control over which files are searched, +use <samp><span class="command">find</span></samp>, <samp><span class="command">grep</span></samp>, and <samp><span class="command">xargs</span></samp>. +For example, the following command searches only C files: + + <pre class="example"> find /home/gigi -name '*.c' -print0 | xargs -0r grep -H 'hello' +</pre> + <p>This differs from the command: + + <pre class="example"> grep -rH 'hello' *.c +</pre> + <p>which merely looks for ‘<samp><span class="samp">hello</span></samp>’ in all files in the current +directory whose names end in ‘<samp><span class="samp">.c</span></samp>’. +Here the <samp><span class="option">-r</span></samp> is +probably unnecessary, as recursion occurs only in the unlikely event +that one of ‘<samp><span class="samp">.c</span></samp>’ files is a directory. +The ‘<samp><span class="samp">find ...</span></samp>’ command line above is more similar to the command: + + <pre class="example"> grep -rH --include='*.c' 'hello' /home/gigi +</pre> + <li>What if a pattern has a leading ‘<samp><span class="samp">-</span></samp>’? + + <pre class="example"> grep -e '--cut here--' * +</pre> + <p class="noindent">searches for all lines matching ‘<samp><span class="samp">--cut here--</span></samp>’. +Without ‘<samp><span class="samp">-e</span></samp>’, +<samp><span class="command">grep</span></samp> would attempt to parse ‘<samp><span class="samp">--cut here--</span></samp>’ as a list of +options. + + <li>Suppose I want to search for a whole word, not a part of a word? + + <pre class="example"> grep -w 'hello' * +</pre> + <p class="noindent">searches only for instances of ‘<samp><span class="samp">hello</span></samp>’ that are entire words; +it does not match ‘<samp><span class="samp">Othello</span></samp>’. +For more control, use ‘<samp><span class="samp">\<</span></samp>’ and +‘<samp><span class="samp">\></span></samp>’ to match the start and end of words. +For example: + + <pre class="example"> grep 'hello\>' * +</pre> + <p class="noindent">searches only for words ending in ‘<samp><span class="samp">hello</span></samp>’, so it matches the word +‘<samp><span class="samp">Othello</span></samp>’. + + <li>How do I output context around the matching lines? + + <pre class="example"> grep -C 2 'hello' * +</pre> + <p class="noindent">prints two lines of context around each matching line. + + <li>How do I force <samp><span class="command">grep</span></samp> to print the name of the file? + + <p>Append <samp><span class="file">/dev/null</span></samp>: + + <pre class="example"> grep 'eli' /etc/passwd /dev/null +</pre> + <p>gets you: + + <pre class="example"> /etc/passwd:eli:x:2098:1000:Eli Smith:/home/eli:/bin/bash +</pre> + <p>Alternatively, use ‘<samp><span class="samp">-H</span></samp>’, which is a <span class="sc">gnu</span> extension: + + <pre class="example"> grep -H 'eli' /etc/passwd +</pre> + <li>Why do people use strange regular expressions on <samp><span class="command">ps</span></samp> output? + + <pre class="example"> ps -ef | grep '[c]ron' +</pre> + <p>If the pattern had been written without the square brackets, it would +have matched not only the <samp><span class="command">ps</span></samp> output line for <samp><span class="command">cron</span></samp>, +but also the <samp><span class="command">ps</span></samp> output line for <samp><span class="command">grep</span></samp>. +Note that on some platforms, +<samp><span class="command">ps</span></samp> limits the output to the width of the screen; +<samp><span class="command">grep</span></samp> does not have any limit on the length of a line +except the available memory. + + <li>Why does <samp><span class="command">grep</span></samp> report “Binary file matches”? + + <p>If <samp><span class="command">grep</span></samp> listed all matching “lines” from a binary file, it +would probably generate output that is not useful, and it might even +muck up your display. +So <span class="sc">gnu</span> <samp><span class="command">grep</span></samp> suppresses output from +files that appear to be binary files. +To force <span class="sc">gnu</span> <samp><span class="command">grep</span></samp> +to output lines even from files that appear to be binary, use the +‘<samp><span class="samp">-a</span></samp>’ or ‘<samp><span class="samp">--binary-files=text</span></samp>’ option. +To eliminate the +“Binary file matches” messages, use the ‘<samp><span class="samp">-I</span></samp>’ or +‘<samp><span class="samp">--binary-files=without-match</span></samp>’ option. + + <li>Why doesn't ‘<samp><span class="samp">grep -lv</span></samp>’ print non-matching file names? + + <p>‘<samp><span class="samp">grep -lv</span></samp>’ lists the names of all files containing one or more +lines that do not match. +To list the names of all files that contain no +matching lines, use the ‘<samp><span class="samp">-L</span></samp>’ or ‘<samp><span class="samp">--files-without-match</span></samp>’ +option. + + <li>I can do <span class="sc">or</span> with ‘<samp><span class="samp">|</span></samp>’, but what about <span class="sc">and</span>? + + <pre class="example"> grep 'paul' /etc/motd | grep 'franc,ois' +</pre> + <p class="noindent">finds all lines that contain both ‘<samp><span class="samp">paul</span></samp>’ and ‘<samp><span class="samp">franc,ois</span></samp>’. + + <li>How can I search in both standard input and in files? + + <p>Use the special file name ‘<samp><span class="samp">-</span></samp>’: + + <pre class="example"> cat /etc/passwd | grep 'alain' - /etc/motd +</pre> + <li><a name="index-palindromes-244"></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: + + <pre class="example"> grep -w -e '\(.\)\(.\).\2\1' file +</pre> + <p>It matches the word "radar" or "civic". + + <p>Guglielmo Bondioni proposed a single RE +that finds all palindromes up to 19 characters long +using 9 subexpressions<!-- /@w --> and 9 back-references<!-- /@w -->: + + <pre class="smallexample"> grep -E -e '^(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?)(.?).?\9\8\7\6\5\4\3\2\1$' file +</pre> + <p>Note this is done by using <span class="sc">gnu</span> ERE extensions; +it might not be portable to other implementations of <samp><span class="command">grep</span></samp>. + + <li>Why is this back-reference failing? + + <pre class="example"> echo 'ba' | grep -E '(a)\1|b\1' +</pre> + <p>This gives no output, because the first alternate ‘<samp><span class="samp">(a)\1</span></samp>’ does not match, +as there is no ‘<samp><span class="samp">aa</span></samp>’ in the input, so the ‘<samp><span class="samp">\1</span></samp>’ in the second alternate +has nothing to refer back to, meaning it will never match anything. +(The second alternate in this example can only match +if the first alternate has matched – making the second one superfluous.) + + <li>What do <samp><span class="command">grep</span></samp>, <samp><span class="command">fgrep</span></samp>, and <samp><span class="command">egrep</span></samp> stand for? + + <p>The name <samp><span class="command">grep</span></samp> comes from the way line editing was done on Unix. +For example, +<samp><span class="command">ed</span></samp> uses the following syntax +to print a list of matching lines on the screen: + + <pre class="example"> global/regular expression/print + g/re/p +</pre> + <p><samp><span class="command">fgrep</span></samp> stands for Fixed <samp><span class="command">grep</span></samp>; +<samp><span class="command">egrep</span></samp> stands for Extended <samp><span class="command">grep</span></samp>. + + </ol> + + </body></html> +
