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diff --git a/slackbook/html/shell-bash.html b/slackbook/html/shell-bash.html new file mode 100644 index 000000000..13ffdf089 --- /dev/null +++ b/slackbook/html/shell-bash.html @@ -0,0 +1,234 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml"> +<head> +<meta name="generator" content="HTML Tidy, see www.w3.org" /> +<title>The Bourne Again Shell (bash)</title> +<meta name="GENERATOR" content="Modular DocBook HTML Stylesheet Version 1.7" /> +<link rel="HOME" title="Slackware Linux Essentials" href="index.html" /> +<link rel="UP" title="The Shell" href="shell.html" /> +<link rel="PREVIOUS" title="The Command Line" href="shell-command-line.html" /> +<link rel="NEXT" title="Virtual Terminals" href="shell-vt.html" /> +<link rel="STYLESHEET" type="text/css" href="docbook.css" /> +<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" /> +</head> +<body class="SECT1" bgcolor="#FFFFFF" text="#000000" link="#0000FF" vlink="#840084" +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='> ' +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 “<var +class="LITERAL">some_value</var>”; 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" +cellspacing="0"> +<tr> +<td width="33%" align="left" valign="top"><a href="shell-command-line.html" +accesskey="P">Prev</a></td> +<td width="34%" align="center" valign="top"><a href="index.html" +accesskey="H">Home</a></td> +<td width="33%" align="right" valign="top"><a href="shell-vt.html" +accesskey="N">Next</a></td> +</tr> + +<tr> +<td width="33%" align="left" valign="top">The Command Line</td> +<td width="34%" align="center" valign="top"><a href="shell.html" +accesskey="U">Up</a></td> +<td width="33%" align="right" valign="top">Virtual Terminals</td> +</tr> +</table> +</div> +</body> +</html> + |