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-<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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-<meta name="generator" content="HTML Tidy, see www.w3.org" />
-<title>The Bourne Again Shell (bash)</title>
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-alink="#0000FF">
-<div class="NAVHEADER">
-<table summary="Header navigation table" width="100%" border="0" cellpadding="0"
-cellspacing="0">
-<tr>
-<th colspan="3" align="center">Slackware Linux Essentials</th>
-</tr>
-
-<tr>
-<td width="10%" align="left" valign="bottom"><a href="shell-command-line.html"
-accesskey="P">Prev</a></td>
-<td width="80%" align="center" valign="bottom">Chapter 8 The Shell</td>
-<td width="10%" align="right" valign="bottom"><a href="shell-vt.html"
-accesskey="N">Next</a></td>
-</tr>
-</table>
-
-<hr align="LEFT" width="100%" />
-</div>
-
-<div class="SECT1">
-<h1 class="SECT1"><a id="SHELL-BASH" name="SHELL-BASH">8.3 The Bourne Again Shell
-(bash)</a></h1>
-
-<div class="SECT2">
-<h2 class="SECT2"><a id="SHELL-BASH-ENVIRONMENT" name="SHELL-BASH-ENVIRONMENT">8.3.1
-Environment Variables</a></h2>
-
-<p>A Linux system is a complex beast, and there's a lot to keep track of, a lot of little
-details that come into play in your normal interactions with various programs (some of
-which you might not even need to be aware of). Nobody wants to pass a bunch of options to
-every program that gets run, telling it what kind of terminal is being used, the hostname
-of the computer, how their prompt should look...</p>
-
-<p>So as a coping mechanism, users have what's called an environment. The environment
-defines the conditions in which programs run, and some of this definition is variable;
-the user can alter and play with it, as is only right in a Linux system. Pretty much any
-shell will have environment variables (if not, it's probably not a very useable shell).
-Here we will give an overview of the commands bash provides for manipulating its
-environment variables.</p>
-
-<p><tt class="COMMAND">set</tt> by itself will show you all of the environment variables
-that are currently defined, as well as their values. Like most <tt
-class="COMMAND">bash</tt> built-ins, it can also do several other things (with
-parameters); we'll leave it to the <tt class="COMMAND">bash</tt>(1) man page to cover
-that, though. <a href="shell-bash.html#EX-SHELL-BASH-ENVIRONMENT">Example 8-1</a> shows
-an excerpt from a <tt class="COMMAND">set</tt> command run on one of the author's
-computers. Notice in this example the <tt class="ENVAR">PATH</tt> variable that was
-discussed earlier. Programs in any of those directories can be run simply by typing the
-base filename.</p>
-
-<div class="EXAMPLE"><a id="EX-SHELL-BASH-ENVIRONMENT"
-name="EX-SHELL-BASH-ENVIRONMENT"></a>
-<p><b>Example 8-1. Listing Environment Variables with <tt
-class="COMMAND">set</tt></b></p>
-
-<table border="0" bgcolor="#E0E0E0" width="100%">
-<tr>
-<td>
-<pre class="SCREEN">
-<samp class="PROMPT">%</samp> <kbd class="USERINPUT">set</kbd>
-PATH=/usr/local/lib/qt/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:
-/usr/openwin/bin:/usr/games:.:/usr/local/ssh2/bin:/usr/local/ssh1/bin:
-/usr/share/texmf/bin:/usr/local/sbin:/usr/sbin:/home/logan/bin
-PIPESTATUS=([0]="0")
-PPID=4978
-PS1='\h:\w\$ '
-PS2='&#62; '
-PS4='+ '
-PWD=/home/logan
-QTDIR=/usr/local/lib/qt
-REMOTEHOST=ninja.tdn
-SHELL=/bin/bash
-</pre>
-</td>
-</tr>
-</table>
-</div>
-
-<table border="0" bgcolor="#E0E0E0" width="100%">
-<tr>
-<td>
-<pre class="SCREEN">
-<samp class="PROMPT">%</samp> <kbd class="USERINPUT">unset <var
-class="REPLACEABLE">VARIABLE</var></kbd>
-</pre>
-</td>
-</tr>
-</table>
-
-<p><tt class="COMMAND">unset</tt> will remove any variables that you give it, wiping out
-both the variable and its value; <tt class="COMMAND">bash</tt> will forget that variable
-ever existed. (Don't worry. Unless it's something you explicitly defined in that shell
-session, it'll probably get redefined in any other session.)</p>
-
-<table border="0" bgcolor="#E0E0E0" width="100%">
-<tr>
-<td>
-<pre class="SCREEN">
-<samp class="PROMPT">%</samp> <kbd class="USERINPUT">export <var
-class="REPLACEABLE">VARIABLE=some_value</var></kbd>
-</pre>
-</td>
-</tr>
-</table>
-
-<p>Now, <tt class="COMMAND">export</tt> is truly handy. Using it, you give the
-environment variable <tt class="ENVAR">VARIABLE</tt> the value &#8220;<var
-class="LITERAL">some_value</var>&#8221;; if <tt class="ENVAR">VARIABLE</tt> didn't exist,
-it does now. If <tt class="ENVAR">VARIABLE</tt> already had a value, well, it's gone.
-That's not so good, if you're just trying to add a directory to your <tt
-class="ENVAR">PATH</tt>. In that case, you probably want to do something like this:</p>
-
-<table border="0" bgcolor="#E0E0E0" width="100%">
-<tr>
-<td>
-<pre class="SCREEN">
-<samp class="PROMPT">%</samp> <kbd class="USERINPUT">export PATH=$PATH:<var
-class="REPLACEABLE">/some/new/directory</var></kbd>
-</pre>
-</td>
-</tr>
-</table>
-
-<p>Note the use of <tt class="ENVAR">$PATH</tt> there: when you want <tt
-class="COMMAND">bash</tt> to interpret a variable (replace it with its value), tack a
-<var class="LITERAL">$</var> onto the beginning of the variable's name. For instance, <tt
-class="COMMAND">echo $PATH</tt> will echo the value of <tt class="ENVAR">PATH</tt>, in my
-case:</p>
-
-<table border="0" bgcolor="#E0E0E0" width="100%">
-<tr>
-<td>
-<pre class="SCREEN">
-<samp class="PROMPT">%</samp> <kbd class="USERINPUT">echo $PATH</kbd>
-/usr/local/lib/qt/bin:/usr/local/bin:/usr/bin:/bin:/usr/X11R6/bin:
-/usr/openwin/bin:/usr/games:.:/usr/local/ssh2/bin:/usr/local/ssh1/bin:
-/usr/share/texmf/bin:/usr/local/sbin:/usr/sbin:/home/logan/bin
-</pre>
-</td>
-</tr>
-</table>
-</div>
-
-<div class="SECT2">
-<h2 class="SECT2"><a id="SHELL-BASH-TAB" name="SHELL-BASH-TAB">8.3.2 Tab
-Completion</a></h2>
-
-<p>(Here comes something cool again.)</p>
-
-<ol type="1">
-<li>
-<p>A commandline interface means lots of typing.</p>
-</li>
-
-<li>
-<p>Typing is work.</p>
-</li>
-
-<li>
-<p>Nobody likes work.</p>
-</li>
-</ol>
-
-<p>From 3 and 2, we can determine that (4) nobody likes typing. Fortunately, <tt
-class="COMMAND">bash</tt> saves us from (5) (nobody likes a commandline interface).</p>
-
-<p>How does <tt class="COMMAND">bash</tt> accomplish this wonderful feat, you ask? In
-addition to the wildcard expansion we discussed before, <tt class="COMMAND">bash</tt>
-features tab completion.</p>
-
-<p>Tab completion works something like this: You're typing the name of a file. Maybe it's
-in your <tt class="ENVAR">PATH</tt>, maybe you're typing it out explicitly. All you have
-to do is type enough of the filename to uniquely identify it. Then hit the tab key. <tt
-class="COMMAND">bash</tt> will figure out what you want and finish typing it for you!</p>
-
-<p>Example time. <tt class="FILENAME">/usr/src</tt> contains two subdirectories: <tt
-class="FILENAME">/usr/src/linux</tt> and <tt class="FILENAME">/usr/src/sendmail</tt>. I
-want to see what's in <tt class="FILENAME">/usr/src/linux</tt>. So I just type <tt
-class="COMMAND">ls /usr/src/l</tt>, hit the <kbd class="USERINPUT">TAB</kbd> key, and <tt
-class="COMMAND">bash</tt> gives me <tt class="COMMAND">ls /usr/src/linux</tt>.</p>
-
-<p>Now, suppose there are two directories <tt class="FILENAME">/usr/src/linux</tt> and
-<tt class="FILENAME">/usr/src/linux-old</tt>; If I type <tt
-class="FILENAME">/usr/src/l</tt> and hit <kbd class="USERINPUT">TAB</kbd>, <tt
-class="COMMAND">bash</tt> will fill in as much as it can, and I'll get <tt
-class="FILENAME">/usr/src/linux</tt>. I can stop there, or I can hit <kbd
-class="USERINPUT">TAB</kbd> again, and <tt class="COMMAND">bash</tt> will show a list of
-directories that match what I've typed so far.</p>
-
-<p>Hence, less typing (and hence, people can like commandline interfaces). I told you it
-was cool.</p>
-</div>
-</div>
-
-<div class="NAVFOOTER">
-<hr align="LEFT" width="100%" />
-<table summary="Footer navigation table" width="100%" border="0" cellpadding="0"
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