forked from pifty/tutes-dump
362 lines
12 KiB
HTML
362 lines
12 KiB
HTML
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<head>
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<title>Basic File and Shell Operations</title>
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<style type="text/css">
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#main {
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width: 800px;
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line-heigth: 1.1em;
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}
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</style>
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</head>
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<body>
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<div id="main">
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<h1>Basic File and Shell Operations</h1>
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<p>In this tutorial, we'll briefly explain some basic file and shell
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operations using the following commands:</p>
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<h2>Commands</h2>
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<ol>
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<li>touch -- create a file</li>
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<li>pwd -- print working directory</li>
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<li>ls -- list files in current directory</li>
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<li>cp -- copy a file</li>
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<li>mv -- move a file</li>
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<li>rm -- remove a file</li>
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<li>file -- examine type of file</li>
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<li>less -- read a file</li>
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<li>mkdir -- create a directory</li>
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<li>cd -- change directory</li>
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<li>rmdir -- remove a directory</li>
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<li>clear -- clear screen</li>
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</ol>
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<p>Please note that the above commands each have a man-page that will
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describe in more detail the full possibilities of each command. In this
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tutorial, we'll simply give a short overview, enough to get things done
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on the command line. For more information on man-pages, see the <a
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href="http://sdf.lonestar.org/index.cgi?tutorials/findinghelp"><i>Finding
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Help From Within the Shell</i></a> tutorial.</p>
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<h3>First some notes about:</h3>
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<ul type="disk">
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<li>Command options</li>
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<li>File naming</li>
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</ul>
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<h3>1. Command options</h3>
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<p>All of the commands above and many commands you'll discover and use
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in the shell can be modified with the use of <i>options</i>. See the
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man-pages for details about the available options for each command.
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<i>Options</i> normally come in the form of <i>ls -l</i>, that is, you
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type the command, space over once, type a dash and the letter for the
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option you need to use.</p>
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Something unique for the SDF server, the SDF server now offers both
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commands with BSD style options and commands with GNU style options.
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For example, <i>ls</i> provides users with a command
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providing BSD style options. The command <i>gls</i>, which is prefixed
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with a "g" designates the <i>ls</i> command providing GNU style options.
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This is very noteworthy because most users are more aquainted with
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binaries with GNU style options. The most popular commands are:
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<i>gls --color=always</i> and <i>gdiff</i>.
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<h3>2. File naming</h3>
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<p>It's good form to name a file or directory without empty spaces in
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the name. A file such as <i>my journal.txt</i> may be more cumbersome
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to handle than a file called <i>my_journal.txt</i>. This is because
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the shell wants to see the above <i>my journal.txt</i> as two separate
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files: one that is called <i>my</i> and another that is called
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<i>journal.txt</i>. If you happen upon a file with empty spaces in
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its name, you can use the following methods to manipulate it:</p>
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<ol>
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<li>Use single or double quotes around the file:
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<ul>
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<li><code>rm "my file.txt"</code> or</li>
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<li><code>cp 'my file.txt' my_file.txt</code>, for example.</li>
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</ul>
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</li>
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<li>Use a backslash where there's an empty space:
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<ul>
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<li><code>mv my\ file.txt my_file.txt</code> or</li>
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<li><code>cd backups/text\ pages/</code>.</li>
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</ul>
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</li>
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<li>Use Tab-Completion: many shells support tab completion. This
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means if you type the first two or three characters of a file name
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and press your Tab button, unless you have multiple files with
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similar beginning names, your shell may be able to finish the word
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completion for you. Note: if you're not in the same directory as
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the file you want to tab complete, you'll need to provide the path,
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which tab-completion can help with also.</li>
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</ol>
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<p>Also, when naming a file using two or more words, the safest
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choices you have to use are the underscore, the dash, and the period.
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Examples are:</p>
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<i>my_file.txt</i><br>
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<i>my-file.txt</i><br>
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<i>my.file.txt</i>
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<p>Or, you can keep it as one word:</p>
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<i>myfile.txt</i>
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<p>Using other symbols, like the ampersand, may cause problems because
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some of these symbols may mean other things to the shell. As always,
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for more information you should read the man-pages for the shell of
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your choice.</p>
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<h3>Commands</h3>
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<p>Note: in the examples below, the percent sign is used to denote the
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command prompt and is not meant to be typed.</p>
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<h3>touch and pwd : create a file and print the working directory</h3>
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<p>To create a file without invoking a text editor or another program,
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one simply has to <i>touch</i> it. For example, to create a file called
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<i>orange.txt</i>, at the command prompt type:</p>
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<code>% touch orange.txt</code>
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<p>Nothing much to that! To see the file you created you have the
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ability to list the file(s) and directories in the current working
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directory. First, let's see which directory we are in. By default,
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upon creating a ssh link or a telnet link to your shell account, you
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will be in your home directory. To confirm this, at the command prompt
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you can type:</p>
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<code>% pwd</code>
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<p>If your user name is georgette, you may get something like this:</p>
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<code>/udd/g/georgette</code>
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<p>Or if you're on your home computer, perhaps you'll see something like
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this:</p>
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<code>/home/georgette</code>
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<h3>ls : list files in current directory</h3>
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<p>Now to list the files in your current directory, type:</p>
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<code>% ls</code>
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<p>If you followed the tutorial and created the <i>orange.txt</i> file
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with the <i>touch</i> command, you should see this file in what the
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<i>ls</i> command yields. Next, try <i>ls</i> with the various
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options below and see the difference in the kinds of information each
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option provides:</p>
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<code>% ls -l</code><br>
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<code>% ls -hl</code><br>
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<code>% ls -a</code><br>
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<code>% ls -al</code><br>
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<code>% ls -ahl</code><br>
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<h3>cp : copy a file</h3>
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<p>Copying a file is likewise very easy. The copy command serves two
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important functions: to make a simple backup of the file in question
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and to also rename a file while keeping the original.</p>
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<p>Say you want to backup your <i>orange.txt</i> file to a
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sub-directory (more about creating directories in a moment) called
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<i>backups</i>. To do so, you would type the following:</p>
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<code>% cp orange.txt backups/</code>
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<p>The forward slash at the end of the word <i>backups</i> means that
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this is a directory.</p>
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<p>To use the <i>cp</i> command to change the name of the file without
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destroying the original you would type the following:</p>
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<code>% cp orange.txt papaya.txt</code>
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<p>where <i>papaya.txt</i> is the new name of the file.</p>
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<p>And to copy the original <i>orange.txt</i> file to the backup
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directory and to change the name at the same time, you would type:</p>
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<code>% cp orange.txt backups/papaya.txt</code>
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<h3>mv : move or rename a file</h3>
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<p>The <i>mv</i> command works similarly to the <i>cp</i> command but
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with one vital difference. Moving a file means destroying the
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original file name. Thus the following command:</p>
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<code>% mv orange.txt papaya.txt</code>
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<p>essentially replaces the <i>orange.txt</i> with the new
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<i>papaya.txt</i> file.</p>
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<p>You can keep the file name the same with the <i>mv</i> command by
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moving the file to a separate directory. To do so, type the
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following:</p>
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<code>% mv orange.txt backups/</code>
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<p>This would move the <i>orange.txt</i> file to the backups
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directory. To move the file to the backups directory and to rename it
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then, you'd type:</p>
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<code>% mv orange.txt backups/papaya.txt</code>
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<h3>rm : remove a file</h3>
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<p>Removing a file is also very simple. The command to do so is
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<i>rm</i>. To completely remove and destroy a file simply type:</p>
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<code>% rm orange.txt</code>
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<h4>short note on interactive use</h4>
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<p>The commands for copying, moving and removing files if carelessly
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used may wreak a bit of havoc for you. For these commands, you may
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want to invoke the interactive option by typing:</p>
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<code>% cp -i orange.txt backups/orange.txt</code><br>
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<code>% mv -i orange.txt papaya.txt</code><br>
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<code>% rm -i orange.txt</code>
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<p>When the interactive option is called, you'll be prompted to answer
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yes or no to each file you are asking to be removed. For
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<i>cp -i</i> and <i>mv -i</i>, you'll be prompted if and only if the file you are
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copying to or moving will overwrite another file.</p>
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<h3>file : examine type of file</h3>
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<p>The <i>file</i> command is useful to determine what type of file a
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file is. In unix-like operating systems, a file's name is fairly
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flexible and the file extension, e.g. the .txt appendage, is not
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always necessary. So if someone sent you a file and you wanted to be
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certain what type of file it was before you opened it, use the
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<i>file</i> command like so:</p>
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<code>% file name_of_file</code>
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<p>The results for a text file would be something like this:</p>
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<code>name_of_file: ASCII text</code>
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<p>Say someone sent you an image file called <i>something.something</i>
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in the PNG format and you wanted to be certain it was actually a PNG
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file, simply type:</p>
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<code>% file something.something</code>
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<p>If the file is truly a PNG file, you should see something similar to
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this:</p>
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<code>something.something: PNG image data, 922 x 691, 8-bit/color RGBA,
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non-interlaced</code>
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<h3>less : read a file</h3>
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<p>The <i>less</i> command is a type of pager available to view
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and browse through text files without altering or opening the file
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in a text editor. You're encouraged to read the man-page for this
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command because it possesses many useful attributes such as
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searching through text for key words or strings. Invoke it with
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the name of the file you want to view:</p>
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<code>% less orange.txt</code>
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<p>If there is more text in the file than can fit on your computer
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screen, press the space-bar to scroll down page by page. Oftentimes,
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your Page Up and Page Down buttons on your keyboard will work and the
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arrow keys normally allow you to go up and down through the file line
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by line.</p>
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<h3>mkdir : create a directory</h3>
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<p>You create a directory by using the <i>mkdir</i> command. To create
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the backups directory we used in earlier examples, type:</p>
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<code>% mkdir backups</code>
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<h3>cd : change directory</h3>
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<p>The <i>cd</i> command is used to change directories. If we are in
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our home directory and want to go to the newly created <i>backups</i>
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sub-directory, we'd simply type:</p>
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<code>% cd backups</code>
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<p>To go back simply type:</p>
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<code>% cd</code>
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<p>Typing <i>cd</i> all by itself will always take you back to your
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home directory which is useful if you're deep in another branch of the
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directory tree. If you just want to go back up a level, type:</p>
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<code>% cd ..</code>
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<p>And of course, you can always type the full path to the directory you
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want to change to:</p>
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<code>% cd /usr/bin</code>
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<p>To switch back to the previous working directory, type:</p>
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<code>% cd -</code>
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<h3>rmdir : remove a directory</h3>
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<p>And to remove an empty directory, you use the the <i>rmdir</i>
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command.</p>
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<code>% rmdir backups</code>
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<p>The <i>rmdir</i> will only work if the directory you want to remove
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is empty of files. If a directory contains files in it and you are sure
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you want to remove said directory along with all the files in it, you
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actually have to go back to the <i>rm</i> command and type:</p>
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<code>% rm -r name_of_directory</code>
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<p>The <i>-r</i> is a command option telling the <i>rm</i> or remove
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command to delete the directory and all contents including
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subdirectories. It stands for <i>recursive</i>. Be very careful
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about using this command! In fact, a better way to run this command
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is by typing:</p>
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<code>% rm -ir</code>
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<p>This invokes the interactive use of the remove command which
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prompts you to answer yes or no to each file and directory to be
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possibly removed. Again, read the man-pages for more details.</p>
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<h3>clear : clear screen</h3>
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<p>Finally, to clear the screen type the following at the prompt:</p>
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<code>% clear</code></br>
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<hr />
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<cite>$Id: file_operations.html,v 1.11 2009/11/28 10:39:54 rogerx Exp $</cite>
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