CS 151 - Introduction to Data Structures

Lab 2

Unix

Using Unix (actually Ubuntu Linux)

If you are working from a personal laptop:

Open a connection onto goldengate with the following command (from a Mac Terminal or Windows Powershell). Note you can connect to goldengate from anywhere in the world using the exact command:

		ssh YOURUNIXNAME@goldengate.cs.brynmawr.edu
	

If you are working at a lab computer:

Open a terminal. To do so: click on the 3x3 grid of dots in the lower left, then scroll through screens until you find Terminal.

• Special names and conventions. Unix has several names that are used with directories. Some are merely by convention, some are built in to UNIX. Here is a partial list with definitions

  root

  the start of the directory structure. The "root" directory is thus the place where everything begins. (In Unix parlance, root can also be used to refer to a person, usually someone who has the power to write in the root directory (ie the power to change anything). In pop culture, this is why the Amy Acker character in the show "person of interest" took the the name "root".)

  home

  the home directory. Each user has a home directory. It is where you are immediately after logging in.

  path

  the way to navigate through directories from the root directory to a given directory (or file)

  ~

  a shortcut. When seen in a path, this denotes the users home directory

  .

  literally a single period. Another shortcut. This indicates the current directory

  ..

  two periods. Another shortcut. This indicates the directory one up from the current directory.

  *

  asterisk. Can be used to substitute for part -- or all - of a file name.

• cd
  Change Directory
  Example: cd CS151 (change to the directory CS151) (Note that this will not work if you do not have a CS151 directory (or you are not in your home directory).)
  Example: cd .. change to the directory one above where you are. For instance if you are in /home/xena/CS151, then cd .. would put you in /home/xena
  Example: cd . change from the current directory to the current directory. This does nothing as you might expect.
  Example: cd with no argument. This returns you to your home directory. (I am not a big fan of this behavior.)
  Example: cd ~ This also returns you to your home directory
  Example: cd ~/CS151 Go to the CS151 directory that is directly under your home directory
  Example: cd / Go to the root directory. (You will almost never have a reason to go to the root directory in this class (other than simple curiosity)).
• ls
  LiSt files
  Display a list of all the files in the directory. It is very common to use the ls command immediately after cd.
  Example: ls list the files in the current directory
  Example: ls CS151 list the files in the directory CS151 (if it exists). Note that CS151 must be contained in the current directory.
  Example: ls ../CS151List the contents of the CS151 directory, that is contained in the directory that contains the current directory.
  Example: ls *.java Within the current directory show all files that end with .java
  Example: ls A*.txt Within the current directory show all files that begin with the letter "A" and end with .txt
• mkdir
  MaKe DIRectory
  Create a directory
  Example: mkdir CS151 make a directory named CS151 You probably already did this in your home directory.
• pwd
  Displays the "current working directory". In other words this command shows you where you are. (I have no idea why pwd is so named)
• cp
  CoPy a file
  Example cp a b make a copy of the file named "a" in the current directory into a file named "b" in the current directory. Note that if "b" existed before the cp command, then it will be overwritten
  Example: cp ~/a a Copy the file named a that is in your home directory to the current directory, keeping the same file name. Note you could also get the same effect from this command cp ~/a .
• mv
  MoVe a file
  Example mv a b change the name of the file a to b. in the current directory. When in the same directory mv can be used to rename files
  Example: mv ~/a a Move the file named a that is in your home directory to the current directory, keeping the same file name. Note you could also get the same effect from this command mv ~/a .
• ssh
  Secure SHell

From the current machine, open a "shell" on a remote machine and interact with that remote machine almost exactly as if you were sitting at it.
Example: ssh YOURUNIXNAME@goldengate.cs.brynmawr.edu Through tis semester, if you like to work on your laptop, I expect that you will use this command frequently. ("goldengate.cs.brynmawr.edu" is the name of a machine accessible via ssh; you cannot directly access the lab machines using ssh.)
• scp
  Secure CoPy a file
  The important difference between cp and scp is that you can use scp to copy between machines. Using scp you can copy either from local to remote (upload) or from reote to local (download).
  Example scp YOURUNIXLOGIN@MACHINEiD:a b make a copy of the file named "a" that is available on the machine MACHINEiDin the home directory of user UNIXLOGIN into a file named "b" in the current directory of the current machine. Note that if "b" existed before the scp command, then it will be overwritten
  Example scp a UNIXLOGIN@MACHINEiD:b Make a copy of the file a in the current directory and put it in the home directory of UNIXLOGIN on MACHINEiD in the name b. It is almost always a good idea in this course for MACHINEiD to be goldengate.cs.brynmawr.edu.
• rm
  ReMove a file
  Example: rm aa Permanently delete the file "aa"
  Example: rm *.class Permanently delete all files that end in .class.
  Danger. Using * with remove can result in you deleting a lot of files.be very cautious. I usually test using ls before rm. For instance "ls *.class" then "rm *.class"
• cat
  Show the entire contents of a file to the terminal. ("cat" was originally an acronym for CAthode ray Tube, which might give you a feel for how long this command has existed.)
  Example: cat aa the entire contents of aa will show on the screen
• javac
  JAVA Compile
  Compile a java program.
  Example: javac HW.java
  This will compile the java code in the file HW.java. If there are no errors, it will create a file HW.class.
• java
  Run a java program.
  Example:java HW
  Run the java program named HW. This requires that the file HW.class is present in the current directory.

Java Practice with inheritance

Now write Younger. Give it two new protected instance variables. Write a constructor that initializes all 4 variables that are a part of Younger. Write a toString that shows all 4 instance variables in Younger. In your Younger toString method, use super.toString(). Write a main method to illustrate what you have done.

After completing all of the above, in your main within Younger add the line

		Older yo = new Younger(1,2,3,4);
		System.out.println(yo);

What gets printed in the added println? Explain.

What to hand in

1. A completed table for the questions in the UNIX section
2. If you worked with someone else, put both names in the subject line.
3. Your Older and Younger implementations.
4. Answers to the questions about Younger.