📄 _chapter 3.htm
字号:
<html>
<head>
<meta name="GENERATOR" content="Microsoft FrontPage 5.0">
<meta name="ProgId" content="FrontPage.Editor.Document">
<meta http-equiv="Content-Type" content="text/html; charset=windows-1252">
<title>Chapter 3</title>
<link rel="stylesheet" type="text/css" href="docsafari.css">
<link rel="stylesheet" type="text/css" href="style.css">
</head>
<body><table width="100%" border="1" bgcolor="#EBEBFF"><tr><td width="5%" align="left" valign="middle"><a href="_chapter 2.htm"><img src="Larrow.gif" width="17" height="19" border="0"></a></td><td align="center" valign="middle"><a class="docLink" href="Front matter.htm">CONTENTS</a></td><td width="5%" align="right" valign="middle"><a href="_chapter 4.htm"><img src="Rarrow.gif" width="17" height="19" border="0"></a></td></tr></table>
<h2 class="docChapterTitle">Chapter 3. The grep Family</h2><ul><li> <a class="docLink" href="#ch03lev1sec1">3.1 The <span class="docEmphasis">grep</span> Command</a></li>
<li> <a class="docLink" href="#ch03lev1sec2">3.2 <span class="docEmphasis">grep</span> Examples with Regular Expressions</a></li>
<li> <a class="docLink" href="#ch03lev1sec3">3.3 <span class="docEmphasis">grep</span> with Pipes</a></li>
<li> <a class="docLink" href="#ch03lev1sec4">3.4 <span class="docEmphasis">grep</span> with Options</a></li>
<li> <a class="docLink" href="#ch03lev1sec5">3.5 <span class="docEmphasis">egrep</span> (Extended <span class="docEmphasis">grep</span>)</a></li>
<li> <a class="docLink" href="#ch03lev1sec6">3.6 Fixed <span class="docEmphasis">grep</span> or Fast <span class="docEmphasis">grep</span></a></li>
<li> <a class="docLink" href="#ch03lev1sec7">UNIX TOOLS LAB EXERCISE</a></li>
</ul>
<p class="docText">
<img alt="graphics/ch03.gif" src="ch03.gif" border="0" width="500" height="411"></p>
<p class="docText">The <span class="docEmphasis">grep</span> family consists of
the commands <span class="docEmphasis">grep, egrep,</span> and
<span class="docEmphasis">fgrep.</span> The <span class="docEmphasis">grep</span>
command globally searches for regular expressions in files and prints all lines
that contain the expression. The <span class="docEmphasis">egrep</span> and
<span class="docEmphasis">fgrep</span> commands are simply variants of
<span class="docEmphasis">grep.</span> The <span class="docEmphasis">egrep</span>
command is an extended <span class="docEmphasis">grep,</span> supporting more
regular expression metacharacters. The <span class="docEmphasis">fgrep</span>
command, called <span class="docEmphasis">fixed grep,</span> and sometimes
<span class="docEmphasis">fast grep,</span> treats all characters as literals;
that is, regular expression metacharacters aren't special梩hey match themselves.
The Free Software Foundation provides a free version of
<span class="docEmphasis">grep,</span> called GNU <span class="docEmphasis">grep.</span>
These versions of <span class="docEmphasis">grep</span> are the ones used on
Linux systems, and can be found in <span class="docEmphasis">/usr/xpg4/bin</span>
on Sun's Solaris OS. The GNU version of <span class="docEmphasis">grep</span>
has extended the basic regular expression metacharacter set, added POSIX
compliancy, and included a number of new command line options. They also provide
a recursive <span class="docEmphasis">grep</span> called
<span class="docEmphasis">rgrep</span> for descending entire directory trees.</p>
<h3 class="docSection1Title" id="ch03lev1sec1">3.1 The <span class="docEmphasis">grep</span>
Command</h3>
<h4 class="docSection2Title" id="ch03lev2sec1">3.1.1 The Meaning of <span class="docEmphasis">grep</span></h4>
<p class="docText">The name <span class="docEmphasis">grep</span> can be traced
back to the <span class="docEmphasis">ex</span> editor. If you invoked that
editor and wanted to search for a string, you would type at the
<span class="docEmphasis">ex</span> prompt:</p>
<pre>: /pattern/p
</pre>
<p class="docText">The first line containing the string
<span class="docEmphasis">pattern</span> would be printed as "<span class="docEmphasis">p</span>"
by the <span class="docEmphasis">print</span> command. If you wanted all the
lines that contained <span class="docEmphasis">pattern</span> to be printed, you
would type:</p>
<pre>: g/pattern/p
</pre>
<p class="docText">When <span class="docEmphasis">g</span> precedes
<span class="docEmphasis">pattern,</span> it means "all lines in the file," or
"perform a global substitution."</p>
<p class="docText">Because the search pattern is called a
<span class="docEmphasis">regular expression,</span> we can substitute
<span class="docEmphasis">RE</span> for <span class="docEmphasis">pattern</span>
and the command reads:</p>
<pre>: g/RE/p
</pre>
<p class="docText">And there you have it: the meaning of
<span class="docEmphasis">grep</span> and the origin of its name. It means "<span class="docEmphasis">g</span>lobally
search for the <span class="docEmphasis">r</span>egular
<span class="docEmphasis">e</span>xpression (<span class="docEmphasis">RE</span>)
and <span class="docEmphasis">p</span>rint out the line." The nice part of using
<span class="docEmphasis">grep</span> is that you do --not have to invoke an
editor to perform a search, and you do not need to enclose the regular
expression in forward slashes. It is much faster than using
<span class="docEmphasis">ex</span> or <span class="docEmphasis">vi.</span></p>
<h4 class="docSection2Title" id="ch03lev2sec2">3.1.2 How <span class="docEmphasis">grep</span>
Works</h4>
<p class="docText">The <span class="docEmphasis">grep</span> command searches
for a pattern of characters in a file or multiple files. If the pattern contains
whitespace, it must be quoted. The pattern is either a quoted string or a single
word<span id="ENB3-1"><a class="docLink" href="#EN3-1"><sup>[1]</sup></a></span>,
and all other words following it are treated as filenames.
<span class="docEmphasis">Grep</span> sends its output to the screen and does
not change or affect the input file in any way.</p>
<div align="center">
<center>
<table cellSpacing="0" width="90%" border="1" style="border-collapse: collapse" bordercolor="#111111" cellpadding="5">
<tr>
<td>
<h2 class="docSidebarTitle">FORMAT</h2>
<pre>grep word filename filename
</pre>
</td>
</tr>
</table>
</center>
</div>
<h5 id="ch03list01" class="docExampleTitle">Example 3.1 </h5>
<pre><span class="docEmphStrong">grep Tom /etc/passwd</span>
</pre>
<div align="center">
<center>
<table cellSpacing="0" width="90%" border="1" style="border-collapse: collapse" bordercolor="#111111" cellpadding="5">
<tr>
<td>
<h2 class="docSidebarTitle">EXPLANATION</h2>
<p class="docText"><span class="docEmphasis">Grep</span> will search for the
pattern <span class="docEmphasis">Tom</span> in a file called
<span class="docEmphasis">/etc/passwd.</span> If successful, the line from
the file will appear on the screen; if the pattern is not found, there will
be no output at all; and if the file is not a legitimate file, an error will
be sent to the screen. If the pattern is found, <span class="docEmphasis">
grep</span> returns an exit status of 0, indicating success; if the pattern
is not found, the exit status returned is 1; and if the file is not found,
the exit status is 2.</p>
<p class="docText">The <span class="docEmphasis">grep</span> program can get
its input from a standard input or a pipe, as well as from files. If you
forget to name a file, <span class="docEmphasis">grep</span> will assume it
is getting input from standard input, the keyboard, and will stop until you
type something. If coming from a pipe, the output of a command will be piped
as input to the <span class="docEmphasis">grep</span> command, and if a
desired pattern is matched, <span class="docEmphasis">grep</span> will print
the output to the screen.</td>
</tr>
</table>
</center>
</div>
<h5 id="ch03list02" class="docExampleTitle">Example 3.2 </h5>
<pre>% <span class="docEmphStrong">ps -ef | grep root</span>
</pre>
<div align="center">
<center>
<table cellSpacing="0" width="90%" border="1" style="border-collapse: collapse" bordercolor="#111111" cellpadding="5">
<tr>
<td>
<h2 class="docSidebarTitle">EXPLANATION</h2>
<p class="docText">The output of the <span class="docEmphasis">ps</span>
command (<span class="docEmphasis">ps 杄f</span> displays all processes
running on this system) is sent to <span class="docEmphasis">grep</span> and
all lines containing <span class="docEmphasis">root</span> are printed.</td>
</tr>
</table>
</center>
</div>
<p class="docText">The <span class="docEmphasis">grep</span> command supports a
number of regular expression metacharacters (see
<a class="docLink" href="#ch03table01">Table 3.1</a>) to help further define the
search pattern. It also provides a number of options (see
<a class="docLink" href="#ch03table02">Table 3.2</a>) to modify the way it does
its search or displays lines. For example, you can provide options to turn off
case sensitivity, display line numbers, display errors only, and so on.</p>
<h5 id="ch03list03" class="docExampleTitle">Example 3.3 </h5>
<pre>% <span class="docEmphStrong">grep -n '^jack:' /etc/passwd</span>
</pre>
<div align="center">
<center>
<table cellSpacing="0" width="90%" border="1" style="border-collapse: collapse" bordercolor="#111111" cellpadding="5">
<tr>
<td>
<h2 class="docSidebarTitle">EXPLANATION</h2>
<p class="docText"><span class="docEmphasis">Grep</span> searches the
<span class="docEmphasis">/etc/passwd</span> file for
<span class="docEmphasis">jack;</span> if <span class="docEmphasis">jack</span>
is at the beginning of a line, <span class="docEmphasis">grep</span> prints
out the number of the line on which <span class="docEmphasis">jack</span>
was found and where in the line <span class="docEmphasis">jack</span> was
found.</td>
</tr>
</table>
</center>
</div>
<p> </p>
<table cellSpacing="0" cellPadding="1" width="100%" border="1">
<caption>
<h5 id="ch03table01" class="docTableTitle">Table 3.1. <span class="docEmphasis">grep</span>'s
Regular Expression Metacharacters</h5>
</caption>
<colgroup span="4" align="left">
</colgroup>
<tr>
<th class="docTableHeader" vAlign="top"><span class="docEmphBoldItalic">
Metacharacter</span> </th>
<th class="docTableHeader" vAlign="top"><span class="docEmphBoldItalic">
Function</span> </th>
<th class="docTableHeader" vAlign="top"><span class="docEmphBoldItalic">
Example</span> </th>
<th class="docTableHeader" vAlign="top"><span class="docEmphBoldItalic">What
It Matches</span> </th>
</tr>
<tr>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">^</span>
</td>
<td class="docTableCell" vAlign="top">Beginning-of-line anchor </td>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">'^love'</span>
</td>
<td class="docTableCell" vAlign="top">Matches all lines beginning with
<span class="docEmphasis">love.</span> </td>
</tr>
<tr>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">$</span>
</td>
<td class="docTableCell" vAlign="top">End-of-line anchor </td>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">'love$'</span>
</td>
<td class="docTableCell" vAlign="top">Matches all lines ending with
<span class="docEmphasis">love.</span> </td>
</tr>
<tr>
<td class="docTableCell" vAlign="top">. </td>
<td class="docTableCell" vAlign="top">Matches one character </td>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">'l..e'</span>
</td>
<td class="docTableCell" vAlign="top">Matches lines containing an
<span class="docEmphasis">l,</span> followed by two characters, followed by
an <span class="docEmphasis">e.</span> </td>
</tr>
<tr>
<td class="docTableCell" vAlign="top">* </td>
<td class="docTableCell" vAlign="top">Matches zero or more characters </td>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">' *love'</span>
</td>
<td class="docTableCell" vAlign="top">Matches lines with zero or more
spaces, followed by the pattern <span class="docEmphasis">love.</span> </td>
</tr>
<tr>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">[ ]</span>
</td>
<td class="docTableCell" vAlign="top">Matches one character in the set </td>
<td class="docTableCell" vAlign="top"><span class="docEmphasis">'[Ll]ove'</span>
</td>
<td class="docTableCell" vAlign="top">Matches lines containing
<span class="docEmphasis">love</span> or <span class="docEmphasis">Love.</span>
</td>
</tr>
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -