Class Overview

The upper-level computer science classes at Rowan used to use the University's Silicon Graphics machines, which run a version of the Unix operating system. (The company later renamed themselves to their initials, "SGI", but when we bought the machines they were still "Silicon Graphics".)

In summer 2002, Elvis (the main CS server which is feeding this web page to you right now) was replaced by a new and more powerful machine from Sun Microsystems. Lots of things changed, but most things didn't.

These computers have some powerful programming tools on them, but making complete use of that power requires understanding a your way around. This class covers many of the fundamentals needed to get maximum use out of advanced Unix machines. Ideally, students will be able to go into their later classes (Compiler Design, Operating Systems, Algorithms, and so on) without having to worry about getting started. When you're in Programming Languages, I hope that you can focus on learning the Programming Language material, instead of having to learn both the PL material and how to use the computers you'll be expected to work on.

Additionally, Unix machines have always been in use by companies that need heavy-duty computing. With the increasing popularity of open-source Unix-like systems such as Linux and BSD, the things covered in Lab Techniques will still be useful after you graduate and enter the job market. Part of my goal in Computer Lab Techniques is that everything we cover will be useful outside of the class: I don't always succeed, but I try every semester to teach only things which will still be useful to you in your next class, and in your job after you graduate.

What I plan to cover, approximately in this order, is as follows:

• Managing your files: creating, renaming, moving, and removing files and directories. Unix systems make it easy to create files: lots and lots of files. You can easily create so many files it later becomes hard to remember what you put where; but there is a program designed to look through your directories and find things for you after you lose them. Combined with the shell's ability to specify groups of files, this lets you do tasks which could be tedious in just a few seconds. (For example, some classes involve running programs which create temporary data files, which can be quite large. During the Fall of 1999, several students reached their disk quota because of their temporary files. Instead of having to delete all of the hundreds of files and directories individually, it was easy to have them removed by the computer -- without also accidentally removing files which were supposed to be kept.) Additionally, unlike other computer systems you may be familiar with, Unix systems make it possible for you to read (and even change) other users' files, and for them to read yours. This can be convenient, but (as with all powerful tools) it requires attention and understand to ensure that it doesn't create other problems. We will therefore give careful attention to file permissions.
• Revision management: keeping track of different versions of the same file. Many modern programs are far too complex to be completed in one step. As a result, programs are written in many parts, usually with different people working on different portions. Additionally, even if a program is working correctly, you may find that you have to make changes to add a new feature, or to change how the program works. Most students find themselves with directories that contain files with names like "homework1.c", "homework1b.c", "homework1b2.c", "homework1b2works.c", "homework1old.c", and so on. It quickly becomes a confusing mess. If you imagine working at a company, and being told to add changes -- and then told later to remove them -- it becomes obvious that what is needed is a tool to keep track of different versions of a program, making the computer do the tedious work of keeping track of what was changed when, while at the same time allowing you to get an old version whenever you want one.
• Compiling tools: programs that help build other programs. Many projects are broken down into separate files, especially in the case of group projects. One student writes one part, another student writes another part, and so on. When it's time to compile all these separate pieces into one working program, how do you remember what goes where? How do you figure out what parts were changed, and what parts weren't, since the last time you compiled? You don't have to remember what parts depend on what other parts, you don't have to figure out what parts were changed. The program "make" will do all of that for you. All you have to do is write a description of your program in the language "make" understands, and it will do the work.
• Debugging tools: programs that help find problems in other programs. Many students, when a program turns out to be buggy, start putting in print statements everywhere in the hopes of finding out what's going wrong. Or worse, they start making random changes in the the hopes of fixing their programs, which is rarely of any help. In many cases, debugging programs can take you directly to the line of your program where the error occurs. They can show you which function called which other function, what the values of your variables are, what's in your arrays. Some can even draw your linked lists on the screen (yes, "draw", just like your instructors do on the blackboard). You can often save hours or even days of time and effort by letting the computer do the work of debugging your programs -- once you know how to use the tools.
• The Command-Line Interface, also known as "the shell", which is the primary method of giving instructions to the system. The shell lets you do sophisticated file matching, write your own commands, and make custom modifications of commands that already exist. It remembers what commands you've run, can re-run them without much typing, and will even let you edit your old commands to correct spelling errors without typing them in again. The shell lets you run several programs at once, stop and re-start what you are doing, and even run programs when you are not logged in to the computer at all.
• The standard Unix filters; programs which can accept many lines of input and filter out the parts you don't want. You can easily have a program which generates 10,000 lines of output, and have a filter set up to show you only the lines you want, and only the parts of those lines that you are interested in. Instead of skimming, or (worse) reading all 10,000 lines -- or, even worse, reading all 10,000 lines only to discover that what you wanted wasn't there -- you can have the computer scan the output for you and locate what you want, often so quickly that you won't have released the "enter" key before the job is done.
• Shell scripting. The command-line interface is more than just a program to read interactive instructions from the keyboard. It can also be used to write small programs. You can work out the commands you'll need interactively, and then combine them into a "shell script" which will execute the same sequence of commands whenever it's needed. One example of this is when you have files with names in ALL UPPERCASE LETTERS, and you want to convert them to lowercase letters. Another example would be when you have two directories, and you need to combine the files in them into one directory. Usually, this means eliminating any files which are duplicated, but keeping files which are slightly different -- and not stomping files just because they have the same names. Done by hand, something like this could take hours. Programmed into a simple script, it can be done in seconds.
• The World Wide Web. Elvis, the main computer science server (which is hosting this page as you are reading it) allows every user to have their own web page. In addition to static pages with a fixed content, you can write small programs, to generate a new web page every time someone visits, or a page customized for a particular user. The files you use have to be kept organized, and when you make changes you often want to keep an archived version of the old file for reference purposes. This gives you an opportunity to write scripts, use the file management tools and revision management tools, and exercise the other things covered in the class.

The reading list is attached separately. Since some classes meet weekly, and others several times a week, this overview is designed to be general. See the page for your specific class section for reading assignments.