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diff --git a/chapter_04.xml b/chapter_04.xml new file mode 100644 index 0000000..0057cb2 --- /dev/null +++ b/chapter_04.xml @@ -0,0 +1,430 @@ +<?xml version="1.0"?> +<!DOCTYPE chapter PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" + "/usr/share/xml/docbook/xml-dtd-4.5/docbookx.dtd"> + +<chapter> +<title>Basic Shell Commands</title> + +<!-- ls, cd, mkdir, touch, rmdir, rm, file --> + +<para> +So you've installed Slackware and you're staring at a terminal prompt, +what now? Now would be a good time to learn about the basic command +line tools. And since you're staring at a blinking curser, you +probably need a little assistance in knowing how to get around, and +that is what this chapter is all about. +</para> + +<section> +<title>System Documentation</title> + +<para> +Your Slackware Linux system comes with lots of built-in documentation +for nearly every installed application. Perhaps the most common method +of reading system documentation is by using the +<application>man</application>(1). <application>man</application> +(short for manual) will bring up the included man-page for any +application, system call, configuration file, or library you tell it +too. For example, <userinput>man man</userinput> will bring up the +man-page for <application>man</application> itself. +</para> + +<para> +Unfortunately, you may not always know what application you need to use +for the task at hand. Thankfully, <application>man</application> has +built-in search abilities. Using the <arg>-k</arg> switch +will cause <application>man</application> to search for every man-page +that matches your search terms. +</para> + +<para> +The man-pages are organized into groups or sections by their content +type. For example, section 1 is for user applications. +<application>man</application> will search each section in order and +display the first match it finds. Sometimes you will find that a +man-page exists in more than one section for a given entry. In that +case, you will need to specify the exact section to look in. In this +book, all applications and a number of other things will have a number +on their right-hand side in parenthesis. This number is the man page +section where you will find information on that tool. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>man -k printf</userinput> +printf (1) - format and print data +printf (3) - formatted output conversion +<prompt>darkstar:~$ </prompt><userinput>man 3 printf</userinput> +</screen> + +<table pgwide="0" frame="none"> +<title>Man Page Sections</title> +<tgroup cols="2"> + <thead> + <row> + <entry>Section</entry> + <entry align="right">Contents</entry> + </row> + </thead> + <tbody> + <row> + <entry>1</entry> + <entry align="right">User Commands</entry> + </row> + <row> + <entry>2</entry> + <entry align="right">System Calls</entry> + </row> + <row> + <entry>3</entry> + <entry align="right">C Library Calls</entry> + </row> + <row> + <entry>4</entry> + <entry align="right">Devices</entry> + </row> + <row> + <entry>5</entry> + <entry align="right">File Formats / Protocols</entry> + </row> + <row> + <entry>6</entry> + <entry align="right">Games</entry> + </row> + <row> + <entry>7</entry> + <entry align="right">Conventions / Macro Packages</entry> + </row> + <row> + <entry>8</entry> + <entry align="right">System Administration</entry> + </row> + </tbody> +</tgroup> +</table> + +</section> + +<section> +<title>Dealing with Files and Directories</title> + + +<section> +<title><application>Listing Files and Directory Contents</application></title> + +<para> +<application>ls</application>(1) is used to list files and directories, +their permissions, size, type, inode number, owner and group, and +plenty of additional information. For example, let's list what's in +the <filename>/</filename> directory for your new Slackware Linux system. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ls /</userinput> +bin/ dev/ home/ lost+found/ mnt/ proc/ sbin/ sys/ usr/ +boot/ etc/ lib/ media/ opt/ root/ srv/ tmp/ var/ +</screen> + +<para>Notice that each of the listings is a directory. These are +easily distinguished from regular files due to the trailing /; standard +files do not have a suffix. Additionally, executable files will have an +asterisk suffix. But <application>ls</application> can do so much +more. To get a view of the permissions of a file or directory, you'll +need to do a "long list". +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ls -l /home/alan/Desktop</userinput> +-rw-r--r-- 1 alan users 15624161 2007-09-21 13:02 9780596510480.pdf +-rw-r--r-- 1 alan users 3829534 2007-09-14 12:56 imgscan.zip +drwxr-xr-x 3 alan root 168 2007-09-17 21:01 ipod_hack/ +drwxr-xr-x 2 alan users 200 2007-12-03 22:11 libgpod/ +drwxr-xr-x 2 alan users 136 2007-09-30 03:16 playground/ +</screen> + +<para> +A long listing lets you view the permisions, user and group ownership, +file size, last modified date, and of course, the file name itself. +Notice that the first two entires are files, and the last three are +directories. This is denoted by the very first character on the line. +Regular files get a "-"; directories get a "d". There are several +other file types with their own denominators. Symbolic links for +example will have an "l". +</para> + +<para> +Lastly, we'll show you how to list dot-files, or hidden files. Unlike +other operating systems such as Microsoft Windows, there is no special +property that differentiates "hidden" files from "unhidden" files. A +hidden file simply begins with a dot. To display these files along +with all the others, you just need to pass the <arg>-a</arg> argument to +<application>ls</application>. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ls -a</userinput> +.xine/ .xinitrc-backup .xscreensaver .xsession-errors SBo/ +.xinitrc .xinitrc-xfce .xsession .xwmconfig/ Shared/ +</screen> + +<para> +You also likely noticed that your files and directories appear in +different colors. Many of the enhanced features of +<application>ls</application> such as these colors or the trailing +characters indicating file-type are special features of the +<application>ls</application> program that are turned on by passing +various arguments. As a convienience, Slackware sets up +<application>ls</application> to use many of these optional arguments +by default. These are controlled by the LS_OPTIONS and LS_COLORS +environment variables. We will talk more about environment variables +in chapter 5. +</para> + +</section> + +<section> +<title>Moving Around the Filesystem</title> + +<para> +<application>cd</application> is the command used to change +directories. Unlike most other commands, <application>cd</application> +is actually not it's own program, but is a shell built-in. Basically, +that means <application>cd</application> does not have its own man +page. You'll have to check your shell's documentation for more details +on the <application>cd</application> you may be using. For the most +part though, they all behave the same. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>cd /</userinput> +<prompt>darkstar:/$</prompt><userinput>ls</userinput> +bin/ dev/ home/ lost+found/ mnt/ proc/ sbin/ sys/ usr/ +boot/ etc/ lib/ media/ opt/ root/ srv/ tmp/ var/ +<prompt>darkstar:/$</prompt><userinput>cd /usr/local</userinput> +<prompt>darkstar:/usr/local$</prompt> +</screen> + +<para> +Notice how the prompt changed when we changed directories? The default +Slackware shell does this as a quick, easy way to see your current +directory, but this is not actually a function of +<application>cd</application>. If your shell doesn't operate in this +way, you can easily get your current working directory with the +<application>pwd</application>(1) command. (Most UNIX shells have +configurable prompts that can be coaxed into providing this same +functionality. In fact, this is another convience setup in the default +shell for you by Slackware.) +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>pwd</userinput> +/usr/local +</screen> + +</section> + +<section> +<title>File and Directory Creation and Deletion</title> + +<para> +While most applications can and will create their own files and +directories, you'll often want to do this on your own. Thankfully, +it's very easy using <application>touch</application>(1) and +<application>mkdir</application>(1). +</para> + +<para> +<application>touch</application> actually modifies the timestamp on a +file, but if that file doesn't exist, it will be created. +</para> + +<screen><prompt>darkstar:~/foo$ </prompt><userinput>ls -l</userinput> +-rw-r--r-- 1 alan users 0 2008-01-18 15:01 bar1 +<prompt>darkstar:~/foo$ </prompt><userinput>touch bar2</userinput> +-rw-r--r-- 1 alan users 0 2008-01-18 15:01 bar1 +-rw-r--r-- 1 alan users 0 2008-01-18 15:05 bar2 +<prompt>darkstar:~/foo$ </prompt><userinput>touch bar1</userinput> +-rw-r--r-- 1 alan users 0 2008-01-18 15:05 bar1 +-rw-r--r-- 1 alan users 0 2008-01-18 15:05 bar2 +</screen> + +<para> +Note how <filename>bar2</filename> was created in our second command, +and the third command simpl updated the timestamp on +<filename>bar1</filename> +</para> + +<para> +<application>mkdir</application> is used for (obviously enough) making +directories. <userinput>mkdir foo</userinput> will create the +directory "foo" within the current working directory. Additionally, +you can use the <arg>-p</arg> argument to create any +missing parent directories. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>mkdir foo</userinput> +<prompt>darkstar:~$ </prompt><userinput>mkdir /slack/foo/bar/</userinput> +mkdir: cannot create directory `/slack/foo/bar/': No such file or directory +<prompt>darkstar:~$ </prompt><userinput>mkdir -p /slack/foo/bar/</userinput> +</screen> + +<para> +In the latter case, <application>mkdir</application> will first create +"/slack", then "/slack/foo", and finally "/slack/foo/bar". If you +failed to use the <arg>-p</arg> argument, +<application>man</application> would fail to create "/slack/foo/bar" +unless the first two already existed, as you saw in the example. +</para> + +<para> +Removing a file is as easy as creating one. The +<application>rm</application>(1) will remove a file (assuming of course +that you have permission to do this). There are a few very common +arguments to <application>rm</application>. The first is +<arg>-f</arg> and is used to force the removal of a file +that you may lack explicit permission to delete. The +<arg>-r</arg> argument will remove directories and their +contents recursively. +</para> + +<para> +There is another tool to remove directories, the humble +<application>rmdir</application>(1). <application>rmdir</application> +will only remove directories that are empty, and complain noisely about +those that contain files or sub-directories. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ls</userinput> +foo_1/ foo_2/ +<prompt>darkstar:~$ </prompt><userinput>ls foo_1</userinput> +bar_1 +<prompt>darkstar:~$ </prompt><userinput>rmdir foo_1</userinput> +rmdir: foo/: Directory not empty +<prompt>darkstar:~$ </prompt><userinput>rm foo_1/bar</userinput> +<prompt>darkstar:~$ </prompt><userinput>rmdir foo_1</userinput> +<prompt>darkstar:~$ </prompt><userinput>ls foo_2</userinput> +bar_2/ +<prompt>darkstar:~$ </prompt><userinput>rm -fr foo_2</userinput> +<prompt>darkstar:~$ </prompt><userinput>ls</userinput> +</screen> + +</section> + +</section> + +<section> +<title>Reading Documents</title> + +<para> +Traditionally, UNIX and UNIX-like operating systems are filled with +text files that at some point in time the system's users are going to +want to read. Naturally, there are plenty of ways of reading these +files, and we'll show you the most common ones. +</para> + +<para> +In the early days, if you just wanted to see the contents of a file +(any file, whether it was a text file or some binary program) you would +use <application>cat</application>(1) to view them. +<application>cat</application> is a very simple program, which takes +one or more files, concatenates them (hence the name) and sends them to +the standard output, which is usually your terminal screen. This was +fine when the file was small and wouldn't scroll off the screen, but +inadequate for larger files as it had no built-in way of moving within +a document and reading it a paragraph at a time. Today, +<application>cat</application> is still used quite extensively, but +predominately in scripts or for joining two or more files into one. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>cat /etc/slackware-version</userinput> +Slackware 12.0.0 +</screen> + +<para> +Given the limitations of <application>cat</application> some very +intelligent people sat down and began to work on an application to let +them read documents one page at a time. Naturally, such applications +began to be known as "pagers". One of the earliest of these was +<application>more</application>(1), named because it would let you see +"more" of the file whenever you wanted. <application>more</application> +will display the first few lines of a text file until your screen is +full, then pause. Once you've read through that screen, you can +proceed down one line by pressing ENTER, or an entire screen by +pressing SPACE. <application>more</application> is also capable of +searching through a text file for keywords. Once you've displayed a +file in <application>more</application>, simply press the / key and +enter a keyword. Upon pressing ENTER, the text will scroll until it +finds the next match. This is clearly a big improvement over +<application>cat</application>, but still suffers from a serious flaw: +<application>more</application> is not able to scroll back up through +the file to allow you to read something you might have missed. Clearly +a better solution is called for. +</para> + +<para> +In order to address the short-comings of +<application>more</application>, a new pager was developed and +ironically dubbed <application>less</application>(1). +<application>less</application> is a very powerful pager that supports +all of the functions of <application>more</application> while adding +lots of additional features. To begin with, +<application>less</application> allows you to use your arrow keys to +controll movement within the document. Due to its popularity, many +Linux distributions have begun to exclude +<application>more</application> in favor of +<application>less</application>. Slackware includes both. Moreover, +Slackware also includes a handy little pre-processor for +<application>less</application> called +<filename>lesspipe.sh</filename>. This allows a user to exectute +<application>less</application> on a number of non-text files. +<filename>lesspipe.sh</filename> will generate text output from running +a command on these files, and display it in +<application>less</application>. +</para> + +</section> + +<section> +<title>Linking</title> + +<para> +Links are a method of referring to one file by more than one name. By +using the <application>ln</application>(1) application, a user can +reference one file with more than one name. The two files are not +carbon-copies of one another, but rather are the exact same file, just +with a different name. To remove the file entirely, all of its names +must be deleted. (This is actually the result of the way that +<application>rm</application> and other tools like it work. Rather +than remove the contents of the file, they simply remove the reference +to the file, freeing that space to be re-used. +<application>ln</application> will create a second reference or "link" +to that file.) +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ln /etc/slackware-version foo</userinput> +<prompt>darkstar:~$ </prompt><userinput>cat foo</userinput> +Slackware 12.0.0 +<prompt>darkstar:~$ </prompt><userinput>ls -l /etc/slackware-version foo</userinput> +-rw-r--r-- 1 root root 17 2007-06-10 02:23 /etc/slackware-version +-rw-r--r-- 1 root root 17 2007-06-10 02:23 foo +</screen> + +<para> +Another type of link exists, the symlink. Symlinks, rather than being +another reference to the same file, are actually a special kind of file +in their own right. These symlinks point to another file or directory. +The primary advantage of symlinks is that they can refer to directories +as well as files, and they can span multiple filesystems. These are +created with the <arg>-s</arg> argument. +</para> + +<screen><prompt>darkstar:~$ </prompt><userinput>ln -s /etc/slackware-version foo</userinput> +<prompt>darkstar:~$ </prompt><userinput>cat foo</userinput> +Slackware 12.0.0 +<prompt>darkstar:~$ </prompt><userinput>ls -l /etc/slackware-version foo</userinput> +-rw-r--r-- 1 root root 17 2007-06-10 02:23 /etc/slackware-version +lrwxrwxrwx 1 root root 22 2008-01-25 04:16 foo -> /etc/slackware-version +</screen> + +<para> +When using symlinks, remember that if the original file is deleted, +your symlink is useless; it simply points at a file that doesn't exist +anymore. +</para> + +</section> + +</chapter> |