Topics

New Material

• We Will Be Using Unix in This Class
• Working with Unix
• Connecting to a Unix Machine
• Your Home Directory
• The Hierarchical Filesystem
• Moving To A Different Directory
• Always Know Where You Are
• Creating A New Directory
• Looking at the Contents of a File
• Compiled versus Interpreted Languages
• Compiled Languages
• Scripting Languages
• Java Works Differently
• Today's Class Exercise

Homework

The first homework assignment is due this Sunday at 11:59 PM.

You will find the assignment here.

If you have a problem or a question, make a post on the Class Discussion Area.

Unix Lab Assistant

An IT student has been stationed in the Unix Lab to you with your Unix questions.

They can also provide basic help with your assignments.

You can find details here.

This link also appears on the class web page.

New Material

We Will Be Using Unix in This Class

• All work in this course will be done on the Unix machine users3.cs.umb.edu
• You will need to connect to this machine from your computer
• This will mean that you will have to learn a few simple Unix commands to do your work
• But it will help you in your professional career
• A great deal of IT work can only be done at the command line

Working with Unix

• Working on the Unix command line takes some getting used to
• There are no menus on the command line
• You must type the name of the command and any arguments it needs
• Then hit Enter (PC) or Return (Mac)
• If you make a mistake you will get an error message which is usually not very helpful
• Fortunately, you only need to know a few Unix commands
• It will be frustrating at first
• But you will soon learn how to do what you need
• Be patient and ask for help in the class discussion area when you run into trouble
• You can also get help from other students
• And people in the Unix Lab on the 3rd floor of McCormack

Connecting to a Unix Machine

• You can connect to Unix machine on which you have an account if you have software that implements the SSH (Secure Shell) protocol
• This software is called an ssh client
• If you have a PC, you need to download an SSH client
• A good free one is PuTTY which you can download here
• You only need the file putty.exe
• You will find instructions on using Windows machine to connect to a Unix machine here
• On a Mac the ssh client is already installed
• To use it, you must go to the Macintosh command line
• It is Terminal program
• Which is located in the Utilities directory inside the Applications directory
• You run the ssh client like this

  ssh YOUR_UNIX_USERNAME@users3.cs.umb.edu

  where you substitute your Unix username for YOUR_UNIX_USERNAME
• You find instructions on connecting to a Unix machine from a Mac here
• You will then have to enter your password

Your Home Directory

• When you first connect to the Unix machine you will be in your home directory
• A directory holds files and other directories
• It is called a folder on Windows and the Mac
• Every Unix account on our system has a home directory
• This directory belongs to you and you alone
• You have complete control over this directory
• If you enter the Unix command ls you will see what is inside this directory
• ls is short for "list"
• If you have completed the Apply process you should see an it114 directory

The Hierarchical Filesystem

• Before we go any further, we needed to talk a little about the way Unix arranges files
• Unix uses a hierarchical filesystem
• Which means that all files are kept in directories (folders)
• And directories live inside other directories
• With one special directory at the top called root
• Which is written as  / 

Moving To A Different Directory

• To move to a different directory you use the cd command
• cd stands for "change directory"
• The command has the following format

  
  cd  NAME_OF_DIRECTORY

• NAME_OF_DIRECTORY is a placeholder
• When you use cd you replace NAME_OF_DIRECTORY with the name of a directory
• To move to your it114 directory, type

  cd  it114

• The hierarchical filesystem can be a little confusing
• If you are ever confused by where you are when connected to Unix, there is a simple fix
• Use the cd command without an argument to go back to your home directory

Always Know Where You Are

• The hierarchical filesystem is like pyramid
• The root directory is at the top
• All other directories are inside this directory
• Or in sub-directories
• Or in sub-sub-Directories
• And so on
• The pyramid gets wider the deeper you go
• Many commands will not work properly if you are in the wrong directory
• Always know where you are in the hierarchical filesystem
• One way to learn your location is to use the pwd command

  $ pwd
  /home/olivia93

• pwd stands for "print working directory"

Creating A New Directory

• You will have to create new directory for each homework assignment
• And for each Class Exercise
• You create a directory using the mkdir command
• mkdir stands for "make directory"
• It has the following format

  
  mkdir DIRECTORY_NAME

• You will have to create two new directories for today's Class Exercise
  • hw
  • ex
• These directories mustbe inside your it114 directory
• Otherwise the scripts I use to score your assignments will not work
• So it is always a good idea to run pwd before using mkdir
• After you create the directories us ls

  $ pwd
  /home/olivia93/it114
  
  $ mkdir hw
  
  $ mkdir ex
  
  $ ls
  ex hw
  

Looking at the Contents of a File

• If you want to see the contents of a Unix file use the cat command
• cat stands for "concatenate"
• A term that will be defined later
• The format for this command is

  
  cat FILENAME

• Here is an example

  $ cat Hello 
  public class Hello {
      public static void main(String[ ]  args)  {
          System.out.println("Hello,  world!") ;
      } 
  }

Compiled versus Interpreted Languages

• When you write a program in you create a text file
• This file consists of statements in the programming language
• This file is called the source code
• But the computer does not understand the language of the source code
• It only understand programs in its own binary machine language
• A program is needed to turn your source code into the binary code the machine understands
• There are two ways a program can do this
  • It can create a new file, translating the source code into machine language
  • It can run the program inside itself, translating the code line by line
• The programs that take the first approach are called compilers
• Programs that take the second approach are called interpreters
• The programming languages that take the first approach are compiled languages
• The programming languages that take the second approach are scripting languages

Compiled Languages

• Language like C and C++ are compiled languages
• You run a C compiler on a C source code file
• And it creates an executable file
• The executable file can then be run on the machine
• Unfortunately, different machines have different machine languages
• So an executable file for one machine will not run on a machine of a different type
• Here is the source code for a simple C program

  #include <stdio.h>
  
  main()
  {
      printf("Hello, world!\n");
  }

• This a program is written in C
• But it is source code, so I cannot run it
• In order to run the program, I must first compile it

  $ gcc hello.c

• gcc is a C compiler
• Running the command above creates an executable file called a.out
• If I had used the -o with gcc I could have given the executable file another name
• a.out is a file that I can run from the command line

  $ ./a.out
  Hello, world!

Scripting Languages

• Languages like Perl, Python and PHP are scripting languages
• In a scripting language the source code is not compiled
• So no executable file is created
• Instead the source code is run inside a program called an interpreter
• Interpreters are written in a compiled language like C
• But they must be compiled for specific machines
• Programs written in a scripting language run more slowly than than compile programs

Java Works Differently

• Java takes a middle course between compiled and interpreted languages
• You take a Java source file and run it through the Java compiler, javac
• The source file must have the .java extension
• The compiler creates an object file with extension .class
• This object file does not contain machine language instructions
• Instead it contains what are called Java bytecodes
• So you cannot run this .class file directly on the machine
• Instead you must run it inside the Java interpreter, java
• The Java interpreter is also called the Java Runtime Environment (JRE)
• Or the Java Virtual Machine (JVM)
• Java interpreters have been written for all major platforms
• That means you can distribute a single set of .class files that will run on most machines
• Java gives developers most of the efficiency of a compiled language
• But the object files can be run almost anywhere

Today's Class Exercise

• In today's Class Exercise you will create directories for your homework assignments
• And your Class Exercises
• These directories must be named hw and ex
• And the must be inside your it114
• You will find the instructions here

Class Quiz

Attendance

Class Exercise