diff options
| author | Patrick J Volkerding <volkerdi@slackware.com> | 2009-08-26 10:00:38 -0500 |
|---|---|---|
| committer | Eric Hameleers <alien@slackware.com> | 2018-05-31 22:41:17 +0200 |
| commit | 5a12e7c134274dba706667107d10d231517d3e05 (patch) | |
| tree | 55718d5acb710fde798d9f38d0bbaf594ed4b296 /slackbook/html/shell-bash.html | |
| download | current-5a12e7c134274dba706667107d10d231517d3e05.tar.gz | |
Slackware 13.0slackware-13.0
Wed Aug 26 10:00:38 CDT 2009
Slackware 13.0 x86_64 is released as stable! Thanks to everyone who
helped make this release possible -- see the RELEASE_NOTES for the
credits. The ISOs are off to the replicator. This time it will be a
6 CD-ROM 32-bit set and a dual-sided 32-bit/64-bit x86/x86_64 DVD.
We're taking pre-orders now at store.slackware.com. Please consider
picking up a copy to help support the project. Once again, thanks to
the entire Slackware community for all the help testing and fixing
things and offering suggestions during this development cycle.
As always, have fun and enjoy! -P.
Diffstat (limited to 'slackbook/html/shell-bash.html')
| -rw-r--r-- | slackbook/html/shell-bash.html | 234 |
1 files changed, 234 insertions, 0 deletions
diff --git a/slackbook/html/shell-bash.html b/slackbook/html/shell-bash.html new file mode 100644 index 00000000..13ffdf08 --- /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> + |