CS 3, Section 1
MiniLecture - Apr 9, 2001

Hello and welcome to today’s CS 3 minilecture. Whether you are officially assigned to this section or otherwise, you are free to attend whichever sections fit your schedule. We hope you find this section informative enough to continue attending.

Personal information

Section 1b : Stephen Bird | bird@ugcs.caltech.edu | Lloyd 223 | x1694

Introduction to Unix

You will need to familiarize yourself with the Unix environment, because that is what all the UGCS computers use. To this end, we have listed a few important commands for navigating Unix. For MS-DOS users, corresponding command is included.

Task	Unix	MS-DOS
Display the contents of a directory	ls	dir
Move to a different directory	cd	cd
Copy file(s) to a new name or a directory	cp [file(s)] [directory or file]	copy [file(s)] [directory or file]
Move file(s) to a directory	mv [file(s)] [directory]	move [file(s)] [directory]
Delete file(s)	rm [file(s)]	del [file(s)]
Rename file	mv [old file] [new file]	rename [old file] [new file]
Make a new directory	mkdir [directory]	mkdir [directory]
Remove a directory	rmdir [directory]	rmdir [directory]

The Unix file system also seems a little tricky at first. Your base directory consists of the directory /home/USERNAME where USERNAME is the name of your UGCS account. From here, you can create whatever directories you want. Say you created a directory for your first lab’s code. Then you wanted to copy the lab 1 code stored in Lab1.java into that directory and return to your home directory. The commands would look something like:

mkdir lab1 -- make the new directory
cp Lab1.java lab1 -- copy the file to the new directory
cd lab1 -- move to the new directory
ls -- check that the file was copied
cd .. -- move down one directory
pwd -- check which directory you are currently in
cd lab1 -- move to the new directory again
ls -- check again for luck that the file was copied
cd ~ -- move to your home directory

Whenever you start an application from the command line in unix, you will be unable to type anything on that command line until you quit the application you just started. For example, if you type emacs at the command prompt, you will have to quit emacs before you can type anything else on the command line. To get around this, add an ampersand "&" after the command, ie. emacs&. This starts the application in background mode. If by accident you already started an application without the &, press Ctrl-z (which suspends the application and returns you to the command line), and type bg in the command line. This places the application into the background and returns you to the command line.

Introduction to emacs

Although you can accomplish all your programming in Netscape, it has been known to hang occasionally. With autosave and recovery features, editors such as emacs and vi are a far better choice. After editing your code, you can then copy and paste the code into Netscape for testing and compiling. Since emacs takes less time to become comfortable with, we have listed a few important commands. Please note that preceding a key with Ctrl- in this chart means pressing the key while holding down the Ctrl or Control key.

Task	Command
Begin emacs	Type emacs at the command prompt
Open a file	Ctrl-x Ctrl-f
Save a file	Ctrl-x Ctrl-s
Search the file for a word or expression	Ctrl-s
Quit emacs	Ctrl-x Ctrl-c

Of course, if you are using the graphical version of emacs, you can do all of that from the menu, which is easier, but slower. Two things with emacs you should watch out for:

Firstly, if you press Ctrl-z emacs will be suspended. Emacs disappears and you are returned to the command line. To return to emacs, simply type bg and press Return to return emacs to the foreground where you can continue working. This actually goes for all applications, as explained before.
Secondly, if you want to search the file but mistakenly start with Ctrl-x, it isn’t intuitive how to quit the command you are working on. Personally, I usually just hit the Escape button a dozen times until it let me back. Instead, you should press Ctrl-g, which will cancel whatever command you were typing.

Running your Java code (finally)

After successfully editing your lab1 program and saving it in your lab1 directory, you’ll need to compile and test it.

For brevity's sake, we'll assume you are compiling and running you java code stored in Lab1.java.
Use the javac compiler to compile your java code into java byte code. javac stands for Java Compiler. javac takes as its arguement your full java code's filename. The command line is javac Lab1.java.
The javac compiler produces java byte code stored in Lab1.class. This file contains your "executable" which will be run in the java virtual machine, much as your scheme program was run in dr. scheme.
Run the program by typing java Lab1. Notice the .class extension is not necessary becuase javac always produces a .class file.
To pass the program arguments, simply append them after the filename. To send the command line arguement "Steve" and "Bird" to your Lab1 program, the command line is java Lab1 Steve Bird.

Suggestions to help introduce yourself to Java