linux tutorial-2.htm

Linux Tutorial

        command line by separating them with semicolons. (Not of interest 
        for now)</FONT></FONT> </LI></UL>
      <P>When changing access privileges the identifiers <B>u</B> - user, 
      <B>g</B> - group and <B>a</B> - everyone are used. For example, this is 
      what is required if everyone is to be allowed to read from and write to 
      <B>file.txt</B>:</P>
      <UL type=circle>
        <LI><B>chmod a+r+w file.txt</B> </LI></UL>
      <P>Directories are a little different to files. They have access 
      privileges that relate to accessing the files within them. For example, 
      when setting the executable privilege to everyone on a directory we simply 
      allow everyone to "move into that directory".</P>
      <P><FONT size=5>3. Wildcards and Variables</FONT></P>
      <P><FONT size=4>3.1 Wildcards (or pattern matching)</FONT></P>
      <P>When using the command line it may be quite time consuming to 
      accomplish certain tasks simply using what we have covered here. For 
      example, you may only wish to list files that match a certain criteria. 
      There is help at hand. One of the most useful "short cuts" is via the use 
      of the <B>*</B> (asterisk) character. Simply stated, the use of <B>*</B> 
      simply allows a user to state "anything goes" in a directory or file name. 
      As an example of its use consider the desire to list all files that begin 
      with the letter "f":&nbsp;</P>
      <UL type=circle>
        <LI><B>ls f*</B> </LI></UL>
      <P>Alternatively, say we require to list all files that end in txt:</P>
      <UL type=circle>
        <LI><B>ls *txt</B> </LI></UL>
      <P>The <B>*</B> is known as a wildcard. There are other wildcards and 
      their use may be summarized as:</P>
      <UL type=circle>
        <LI><B>* </B>(asterisk) - matches zero or more characters in a file 
        name. Therefore <B>a*</B> matches the names <B>a</B>, <B>ab</B>, 
        <B>abc</B>, etc. <B>*</B> by itself matches all file names with certain 
        exceptions to be noted. 
        <LI><B>? </B>(question mark) - matches exactly one character in a file 
        name. Therefore <B>a?</B> matches <B>ab</B>, <B>ac</B>, but not a nor 
        <B>abc</B>. 
        <LI><B>\ </B>(backslash) treat the character following the <B>\</B> as a 
        non special character. Therefore, you can refer to a file named: 
        <B>e?b</B> as <B>e\?b</B>. </LI></UL>
      <P><FONT size=4>3.2 Environmental variables</FONT></P>
      <P>Variables exist within the command line environment. Variables are 
      identified by the <B>$</B> (dollar sign) that proceeds them. You can 
      substitute any hard coded data with variables. For example, you can return 
      to your <B>$HOME</B> directory whenever you wish by simply typing:</P>
      <UL type=circle>
        <LI><B>cd $HOME</B> </LI></UL>
      <P>&nbsp;Here are some useful variables that may be used:</P>
      <UL type=circle>
        <LI><TT class=VARNAME><B>$HOME - </B></TT>Home directory of the user, 
        usually <TT class=FILENAME>/home/username</TT> 
        <LI><B><TT class=VARNAME>$HOSTNAME - </TT></B>Name assigned to the 
        system, usually fetched at bootup from <TT 
        class=FILENAME>/etc/hosts</TT> 
        <LI><B><TT class=VARNAME>$UID - </TT></B>User id number 
        <LI>Current user's user identification number, as recorded in <TT 
        class=FILENAME>/etc/passwd</TT> 
        <LI><TT class=VARNAME><B>$EUID - </B></TT><SPAN 
        class=QUOTE>"Effective"</SPAN> user id number 
        <LI>may be different from $UID as the user may sometimes assume other 
        IDs (don't worry about this issue for now) 
        <LI><B><TT class=VARNAME>$GROUPS - </TT></B>Groups current user belongs 
        to 
        <LI>This is a listing (array) of the group id numbers for current user, 
        as recorded in <TT class=FILENAME>/etc/passwd</TT>. 
        <LI><B><TT class=VARNAME>$PATH - </TT></B>Path to binaries, usually <TT 
        class=FILENAME>/usr/bin/</TT>, <TT class=FILENAME>/usr/X11R6/bin/</TT>, 
        <TT class=FILENAME>/usr/local/bin</TT>, etc. 
        <LI>When given a command, the shell automatically searches the 
        directories listed in the <EM>path</EM> for the executable. The path is 
        stored in the environmental variable, <TT class=VARNAME>$PATH</TT>, a 
        list of directories, separated by colons. Normally, the system stores 
        the <TT class=VARNAME>$PATH</TT> definition in <TT 
        class=FILENAME>/etc/profile</TT>&nbsp; 
        <P><TT class=USERINPUT><B>PATH=${PATH}:/opt/bin</B></TT> appends the <TT 
        class=FILENAME>/opt/bin</TT> directory to the current path.</P>
        <DIV class=NOTE>
        <BLOCKQUOTE class=NOTE>
          <P><B>Note: </B>The current <SPAN class=QUOTE>"working 
          directory"</SPAN>, <TT class=FILENAME>./</TT>, is usually omitted from 
          the <TT class=VARNAME>$PATH</TT> as a security 
        measure.</P></BLOCKQUOTE></DIV>
        <LI>The following are provided for information only: 
        <LI><FONT color=#c0c0c0><TT class=VARNAME><B>$PS1 - </B></TT>This is the 
        main prompt, seen at the command line.</FONT> 
        <LI><FONT color=#c0c0c0><TT class=VARNAME><B>$PS2 - </B></TT>The 
        secondary prompt, seen when additional input is expected. It displays as 
        <SPAN class=QUOTE>"&gt;"</SPAN>.</FONT> 
        <LI><FONT color=#c0c0c0><TT class=VARNAME><B>$PS3 - </B></TT>The 
        tertiary prompt, displayed in a <B class=COMMAND>select</B>.</FONT> 
        <LI><FONT color=#c0c0c0><TT class=VARNAME><B>$PS4 - </B></TT>The 
        quartenary prompt, shown at the beginning of each line of output when 
        invoking a script with the <SPAN class=TOKEN>-x</SPAN> option. It 
        displays as <SPAN class=QUOTE>"+"</SPAN>.</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$PWD - </TT></B>Working 
        directory (directory you are in at the time)</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$OLDPWD - </TT></B>Old 
        working directory (previous directory you were in)</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$DIRSTACK - 
        </TT></B>Contents of the directory stack</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$PPID - </TT></B>The 
        process id (pid) of the currently running process.</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$MACHTYPE - 
        </TT></B>Machine type, Identifies the system hardware.</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$HOSTTYPE - </TT></B>Host 
        type</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$OSTYPE - 
        </TT></B>Operating system type.</FONT> 
        <LI><FONT color=#c0c0c0><B><TT class=VARNAME>$EDITOR - </TT></B>The 
        default editor invoked by a script, usually <B class=COMMAND>vi</B> or 
        <B class=COMMAND>emacs</B>.</FONT> </LI></UL>
      <P>When you log in a special script (more about scripts later) is parsed 
      and the shell updates environmental variables automatically at logging in 
      time (without you having to set variables each time you log in). This is 
      commonly found in the <B>.profile</B> file. A sample <B>.profile</B> file 
      may look like this:</P>
      <P><B>PATH=:$HOME:/bin:/usr/bin:/usr/local/bin:/usr/local/X11/bin:/usr/local/X11-local<BR>:/usr/openwin/bin:usr/ccs/bin:/usr/ucb:/usr/local/CC/current/bin:/usr/ccs/bin:/u<BR>sr/local/JavaIDL/current/bin:/usr/local/JavaIDL/current/bin<BR>export 
      PATH<BR>PRINTER=durian&nbsp;<BR>export 
      PRINTER<BR>OMNIORB_CONFIG=$HOME/omniORB.cfg<BR>export 
      OMNIORB_CONFIG<BR>EDITOR=/usr/local/bin/memacs<BR>export 
      DISPLAY<BR>VISUAL=/usr/local/bin/emacs<BR>MANPATH=/usr/share/man:/usr/local/man:/usr/local/X11R5/man:/usr/local/CC/current<BR>/man<BR>CVSROOT=/usr/share/src/arjuna.cvs<BR>X11HOME=/usr/local/X11<BR>LD_LIBRARY_PATH=/usr/local/X11/lib:/usr/ucblib:/lib:/usr/local/jdk/lib:/usr/loca<BR>l/JavaIDL/current/lib:/usr/local/omniORB/2.7.1/lib/i586_linux_2.0_glibc<BR>export 
      LD_LIBRARY_PATH<BR></B></P>
      <P><FONT size=4>3.3 Online help</FONT></P>
      <P>The number of ways a command can be used tends to be diverse. 
      Therefore, there is a help system that identifies how commands may be 
      used. This command system is commonly known as <B>man</B> (short for 
      manual). If ever you want to know more about a command, placing man before 
      the command name will bring up a useful help sheet, describing how the 
      command may be used. For example, if I want to know how <B>ls</B> may be 
      used you can simply type:</P>
      <UL type=circle>
        <LI><B>man ls</B> 
        <LI><B>NOTE - To get out of the man page listing press the "q" key and 
        to scroll the man page listing press space.</B> </LI></UL>
      <P>Another helpful aspect of executable programs (not usually basic 
      commands like <B>ls</B>) is that they usually (but not always) come with 
      help sheets built in. This is commonly accessed via the name of the 
      command followed by a <B>-</B> (dash) and <B>h</B> (or <B>help</B>). For 
      example, there is a simple program available on most Linux systems that 
      manages your email called <B>pine</B>. If I wanted help on how <B>pine</B> 
      works I could simply type:</P>
      <UL type=circle>
        <LI><B>pine -help</B> </LI></UL>
      <HR>

      <P><FONT size=5>Exercises</FONT></P>
      <P><FONT color=#c0c0c0><B>1)</B> Login and change your password</FONT> 
      (NOT POSSIBLE ON YOUR SYSTEM - MISS THIS QUESTION OUT).</P>
      <P><B>2)</B> Make a directory called "myDirectory" in your home 
      directory.</P>
      <P><B>3)</B> Using the program "nedit" create a text file that contains 
      your name and call this file "myDetails".</P>
      <P><B>4)</B> From inside the directory "myDirectory" make the directory 
      tree "myFiles/text/tmp".</P>
      <P><B>5)</B> Move the "myDetails" file to the newly created "tmp" 
      directory.</P>
      <P><B>6)</B> Make a directory in the "myFiles" directory and call it 
      "bin".</P>
      <P><B>7)</B> Create a copy of the directory tree which has the root 
      directory of "myDirectory" and call "myWork".</P>
      <P><B>8)</B> Remove, via a single command, the whole directory tree that 
      has the root directory "myDirectory".</P>
      <P>&nbsp;</P>
      <P>&nbsp;</P>
      <P>&nbsp;</P></TD></TR></TBODY></TABLE></BODY></HTML>