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diff --git a/misc/slackbook/html/shell-command-line.html b/misc/slackbook/html/shell-command-line.html new file mode 100644 index 00000000..6188bd95 --- /dev/null +++ b/misc/slackbook/html/shell-command-line.html @@ -0,0 +1,307 @@ +<!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 Command Line</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 Shell" href="shell.html" /> +<link rel="NEXT" title="The Bourne Again Shell (bash)" href="shell-bash.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.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-bash.html" +accesskey="N">Next</a></td> +</tr> +</table> + +<hr align="LEFT" width="100%" /> +</div> + +<div class="SECT1"> +<h1 class="SECT1"><a id="SHELL-COMMAND-LINE" name="SHELL-COMMAND-LINE">8.2 The Command +Line</a></h1> + +<div class="SECT2"> +<h2 class="SECT2"><a id="SHELL-COMMAND-LINE-RUNNING" +name="SHELL-COMMAND-LINE-RUNNING">8.2.1 Running Programs</a></h2> + +<p>It's hard to get much accomplished without running a program; you might be able to +prop something up with your computer or hold a door open, and some will make the most +lovely humming noise when running, but that's really about it. And I think we can all +agree that its use as a humming doorstop isn't what brought the personal computer the +popularity it now enjoys.</p> + +<p>So, remember how almost everything in Linux is a file? Well, that goes for programs, +too. Every command you run (that isn't built into the shell) resides as a file somewhere. +You run a program simply by specifying the full path to it.</p> + +<p>For instance, remember that <tt class="COMMAND">su</tt> command from the last section? +Well, it's actually in the <tt class="FILENAME">/bin</tt> directory: <tt +class="COMMAND">/bin/su</tt> would run it nicely.</p> + +<p>So why, then, does just typing <tt class="COMMAND">su</tt> work? After all, you didn't +say it was in <tt class="FILENAME">/bin</tt>. It could just as easily have been in <tt +class="FILENAME">/usr/local/share</tt>, right? How did it <span class="emphasis"><i +class="EMPHASIS">know</i></span>? The answer to that lies in the <tt +class="ENVAR">PATH</tt> environment variable; most shells have either <tt +class="ENVAR">PATH</tt> or something very much like <tt class="ENVAR">PATH</tt>. It +basically contains a list of directories to look in for programs you try to run. So when +you ran <tt class="COMMAND">su</tt>, your shell ran through its list of directories, +checking each one for an executable file called <tt class="COMMAND">su</tt> that it could +run; the first one it came to, it ran. This happens whenever you run a program without +specifying a full path to it; if you get a ““<tt class="ERRORNAME">Command +not found</tt>”” error, that only means that the program you tried to run +isn't in your <tt class="ENVAR">PATH</tt>. (Of course, this would be true if the program +doesn't exist at all...) We'll discuss environment variables in more depth in <a +href="shell-bash.html#SHELL-BASH-ENVIRONMENT">Section 8.3.1</a>.</p> + +<p>Remember also that “<tt class="FILENAME">.</tt>” is shorthand for the +current directory, so if you happened to be in <tt class="FILENAME">/bin</tt>, <tt +class="FILENAME">./su</tt> would have worked as an explicit full path.</p> +</div> + +<div class="SECT2"> +<h2 class="SECT2"><a id="SHELL-COMMAND-LINE-WILDCARD" +name="SHELL-COMMAND-LINE-WILDCARD">8.2.2 Wildcard Matching</a></h2> + +<p>Nearly every shell recognizes some characters as being substitutes or abbreviations +that mean anything goes here. Such characters are aptly named wildcards; the most common +are <var class="LITERAL">*</var> and <var class="LITERAL">?</var>. By convention, <var +class="LITERAL">?</var> usually matches any single character. For instance, suppose +you're in a directory with three files: <tt class="FILENAME">ex1.txt</tt>, <tt +class="FILENAME">ex2.txt</tt>, and <tt class="FILENAME">ex3.txt</tt>. You want to copy +all of those files (using the <tt class="COMMAND">cp</tt> command we cover in <a +href="file-commands-copymove.html#FILE-COMMANDS-COPYMOVE-CP">Section 10.5.1</a>) to +another directory, say <tt class="FILENAME">/tmp</tt>. Well, typing <tt +class="COMMAND">cp ex1.txt ex2.txt ex3.txt /tmp</tt> is entirely too much work. It's much +easier to type <tt class="COMMAND">cp ex?.txt /tmp</tt>; the <var class="LITERAL">?</var> +will match each of the characters “1”, “2”, and “3”, +and each in turn will be substituted in.</p> + +<p>What's that you say? That's <span class="emphasis"><i +class="EMPHASIS">still</i></span> too much work? You're right. It's appalling; we have +labor laws to protect us from that sort of thing. Fortunately, we also have <var +class="LITERAL">*</var>. As was already mentioned, <var class="LITERAL">*</var> matches +“any number of characters”, including 0. So if those three files were the +only ones in the directory, we could have simply said <tt class="COMMAND">cp * /tmp</tt> +and gotten them all in one fell swoop. Suppose, though, that there is also a file called +<tt class="FILENAME">ex.txt</tt> and one called <tt class="FILENAME">hejaz.txt</tt>. We +want to copy <tt class="FILENAME">ex.txt</tt> but not <tt +class="FILENAME">hejaz.txt</tt>; <tt class="COMMAND">cp ex* /tmp</tt> will do that for +us.</p> + +<p><tt class="COMMAND">cp ex?.txt /tmp</tt>, would, of course, only get our original +three files; there's no character in <tt class="FILENAME">ex.txt</tt> to match that <var +class="LITERAL">?</var>, so it would be left out.</p> + +<p>Another common wildcard is the bracket pair <var class="LITERAL">[ ]</var>. Any +characters inside the brackets will be substituted in place of the <var class="LITERAL">[ +]</var> to find matches. Sound confusing? It's not too bad. Suppose for instance, we have +a directory containing the following 8 files: <tt class="FILENAME">a1</tt>, <tt +class="FILENAME">a2</tt>, <tt class="FILENAME">a3</tt>, <tt class="FILENAME">a4</tt>, <tt +class="FILENAME">aA</tt>, <tt class="FILENAME">aB</tt>, <tt class="FILENAME">aC</tt>, and +<tt class="FILENAME">aD</tt> . We want to only find the files ending in numbers; <var +class="LITERAL">[ ]</var> will do this for us.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ls a[1-4]</kbd> +a1 a2 a3 a4 +</pre> +</td> +</tr> +</table> + +<p>But what we really want is just <tt class="FILENAME">a1</tt>, <tt +class="FILENAME">a2</tt>, and <tt class="FILENAME">a4</tt>? In the previous example we +used - to mean all values between 1 and 4. We can also separate individual entries with +commas.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ls a[1,2,4]</kbd> +a1 a2 a4 +</pre> +</td> +</tr> +</table> + +<p>I know what you're thinking now, “Well what about letters?” Linux is +case-sensitive, meaning that <var class="LITERAL">a</var> and <var +class="LITERAL">A</var> are different characters and are only related in your mind. +Capitals always come before lowercase letters, so <var class="LITERAL">A</var> and <var +class="LITERAL">B</var> come before <var class="LITERAL">a</var> and <var +class="LITERAL">b</var>. Continuing with our earlier example, if we wanted files <tt +class="FILENAME">a1</tt>, and <tt class="FILENAME">A1</tt>, we can find these quickly +with <var class="LITERAL">[ ]</var>.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ls [A,a]1</kbd> +A1 a1 +</pre> +</td> +</tr> +</table> + +<p>Note, that if we had included a hyphen instead of a comma, we would have gotten +incorrect results.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ls [A-a]1</kbd> +A1 B1 C1 D1 a1 +</pre> +</td> +</tr> +</table> + +<p>You can also combine hyphen and comma strings.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ls [A,a-d]</kbd> +A1 a1 b1 c1 d1 +</pre> +</td> +</tr> +</table> +</div> + +<div class="SECT2"> +<h2 class="SECT2"><a id="SHELL-COMMAND-LINE-PIPING" +name="SHELL-COMMAND-LINE-PIPING">8.2.3 Input/Output Redirection and Piping</a></h2> + +<p>(Here comes something cool.)</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ps > blargh</kbd> +</pre> +</td> +</tr> +</table> + +<p>Y'know what that is? That's me running <tt class="COMMAND">ps</tt> to see which +processes are running; <tt class="COMMAND">ps</tt> is covered in <a +href="process-control-ps.html">Section 11.3</a>. That's not the cool part. The cool part +is <var class="LITERAL">> blargh</var>, which means, roughly, take the output from <tt +class="COMMAND">ps</tt> and write it to a file called <tt class="FILENAME">blargh</tt>. +But wait, it gets cooler.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ps | less</kbd> +</pre> +</td> +</tr> +</table> + +<p>That one takes the output from <tt class="COMMAND">ps</tt> and pipes it through <tt +class="COMMAND">less</tt>, so I can scroll through it at my leisure.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ps >> blargh</kbd> +</pre> +</td> +</tr> +</table> + +<p>This is the third most commonly used redirector; it does the same thing as +“>”, except that “>>” will append output from <tt +class="COMMAND">ps</tt> to the file <tt class="FILENAME">blargh</tt>, if said file +exists. If not, just like “>”, it will be created. (“>” +will obliterate the current contents of <tt class="FILENAME">blargh</tt>.)</p> + +<p>There is also a “<” operator, which means take your input from the +following, but it's not used nearly so often.</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd +class="USERINPUT">fromdos < dosfile.txt > unixfile.txt</kbd> +</pre> +</td> +</tr> +</table> + +<p>Redirection gets really fun when you start piling it up:</p> + +<table border="0" bgcolor="#E0E0E0" width="100%"> +<tr> +<td> +<pre class="SCREEN"> +<samp class="PROMPT">%</samp> <kbd class="USERINPUT">ps | tac >> blargh</kbd> +</pre> +</td> +</tr> +</table> + +<p>That will run <tt class="COMMAND">ps</tt>, reverse the lines of its output, and append +those to the file <tt class="FILENAME">blargh</tt>. You can stack as many of these up as +you want; just be careful to remember that they get interpreted from left to right.</p> + +<p>See the <tt class="COMMAND">bash</tt>(1) man page for more detailed information on +redirection.</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.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-bash.html" +accesskey="N">Next</a></td> +</tr> + +<tr> +<td width="33%" align="left" valign="top">The Shell</td> +<td width="34%" align="center" valign="top"><a href="shell.html" +accesskey="U">Up</a></td> +<td width="33%" align="right" valign="top">The Bourne Again Shell (bash)</td> +</tr> +</table> +</div> +</body> +</html> + |