Intro to Unix

Due Date:

Wednesday, September 12th, 2007.

Introduction:

Before we get into programming proper, we need a few fundamental survival skills which we will use to control our environment. Since this will be a mostly paperless classroom, you will need to be able to do two things before we can do anything else:

1. Find your way around the UNIX Operating System.
2. Create and edit files with the vi text editor.

Let's begin with the first of those goals.

Description:

We will begin class today with a discusion of file systems. We will talk about what a file system is and look briefly at the Unix file system. After that, we will hava a web activity exploring basic unix commands we will need to manage our computing environment in Computer Science.

Activities

1. At the unix command prompt ( $ ), type: links2. links2 is a text based web browser (we also have the older lynx browser installed on the system). Your screen will go blank. Now press the g key. This is where you can enter a web address. Pressing q will offer you the option to quit. There are two keys which will bring up a menu at the top of the screen. To find these, run: man links2 at the command prompt and read through the man page (man is short for manual).
   
   
2. Using the web resources listed at the bottom of this page (and any other resources you would like to use), write out a description and an example for each of the Unix commands in the list that follows:
   • ls
   • pwd
   • cd
   • mkdir
   • rmdir
   • cp
   • mv
   • rm
   • rm -rf
   • man
   • cat
   
   
   
3. In your home directory (/home/username), create a directory named computer_science, then change to this directory (pwd should return /home/your_username/computer_science when you are finished). Create the following subdirectories in the computer_science directory: programs, notes, and projects. Running pwd now you should see this:

        /home/username/computer_science
     

   and running ls should give you this:

       notes  programs  projects
     

   In the programs directory, create four more subdirectories named gvr, python, java, and c.
   
   
4. The next skill you will need to master is to use a text editor. The editor we will use in this class is called vim. To learn to use vim, type the following at the unix prompt:

     $ vimtutor
     

   Follow along with this tutorial, trying out all the activities which it provides.
   
   
5. A common task on a Unix system is compiling and installing software. For your last activity, you will install and run a useful tool for displaying the structure and contents of your file system. Since most software on a GNU/Linux system is free software, it is often the case that source code is downloaded directly, compiled, and installed. In this activity we will do just that.
   
   
   • Change to the c subdirectory of the programs directory (Hint: the path should be: /home/username/computer_science/programs/c ).
     
     
   • Press the d on the link to download the file tree-1.5.0.tgz. Move this file into the c directory. This is a compressed (zipped), archieve file containing source code for a little utility program called tree.
     
     
   • To extract the files from the archieve, type:

         tar xzvf tree-1.5.0.tgz
         

   • This will extract a directory named tree-1.5.0 containing six files.
     
     
   • Change to this directory and run the command make from the command prompt. This will compile the source file into a binary, or executable file which can be run by the operating system.
     
     
   • type: ./tree and you will see the following output:

         .
         |-- CHANGES
         |-- LICENSE
         |-- Makefile
         |-- README
         |-- tree
         |-- tree.1
         |-- tree.c
         `-- tree.o
         

     If you move the file named tree (the executable file) into the computer_science directory, and run ./tree again, you will see this:

         .
         |-- notes
         |-- programs
         |   |-- c
         |   |   |-- tree-1.5.0
         |   |   |   |-- CHANGES
         |   |   |   |-- LICENSE
         |   |   |   |-- Makefile
         |   |   |   |-- README
         |   |   |   |-- tree.1
         |   |   |   |-- tree.c
         |   |   |   `-- tree.o
         |   |   `-- tree-1.5.0.tgz
         |   |-- gvr
         |   |-- java
         |   `-- python
         |-- projects
         `-- tree
         

     How would you describe what tree does?
     
     
   • The last thing to do is to make the tree available at all times and from within any directory. To do this we need to set the PATH environment variable. This is a rather involved process, so follow these instructions step-by-step with care:
     
     
     • At the unix command prompt, type echo $HOME. What does this command return? Now type: echo $PATH. Write down on a piece of paper what this command returns.
       
       
     • PATH is an environment variable that stores the search path on the system. There are several directory paths separated by colons ( : ). When you type a command, like links2, the operating system searches each directory in the path, looking for a match to what you typed. The first time a match is found, the command is executed. If no match is found, you will get back a message like this:

             -bash: tree: command not found
             

       To see this in action, change to your home directory and type tree at the command prompt.
       
       
     • Our goal now is to create a place for you to put commands that you would like to add, and to set the search path so that the operating system can find them. A good place to put binary files like tree is in a directory named bin (notice how many bin directories where in the search path). So, make a directory named bin in your home directory.
       
       
     • Move the tree file to this new bin directory.
       
       
     • Now we will set the environment variable, PATH to include the new bin directory. Before making this automatic, let's see how it works. Type the following command at the unix prompt:

             $ echo $HOME/bin:$PATH
             

       Notice how is this different from what you see when you type:

             $ echo $PATH
             

     • To set this variable in your running environment, type:

             $ export PATH=$HOME/bin:$PATH
             

     • Finally, to make it automatic on log-in, add the following to the botton of your .bashrc file, which is located in your home directory:

             PATH=$HOME/bin:$PATH
       
             export PATH
             

       You will need to use a text editor like vi to do this.

Congratulations! You have just completed our introduction to Unix.

Evaluation

The evaluation for this lesson will consist of a performance exercise. You will select at random (I'll tell you in class about how the selection process will work) a task to be performed. Tasks will look something like this:

1. Create a directory named sports in your home directory.
   
   
2. Create subdirectories in the sports directory named baseball, football, basketball, and soccer.
   
   
3. Create a file named stars.txt in the baseball directory. Add the names of three baseball stars, one per line, to this file. If you don't know the names of any baseball stars, just make up three names.
   
   
4. Repeat the previous step in each of the other subdirectories of the sports directory.

The complete list of tasks can be found here.

Web Resources:

• UNIX Tutorial for Beginners
• Getting Started with Unix
• UNIXhelp for users