Lesson 1

PC vs. Multi-user System

Personal Computer – each user gets his/her own processor (or multicore processor).

Multi-user system – The processor, RAM, disk, and i/o devices are shared among several users.

This can be accomplished through:multitaskingtimesharing

What is an Operating System?An OS is software (i.e. a computer

program) that manages your computer.

Its main jobs are: Manage software Enable interaction with a user Control peripherals (e.g. disk, printer)

What is UNIX?

Unix is an operating system for multi-user systems.

Developed originally at Bell Labs in 1969 by Thompson and Ritchie.

It is an Open System (no single company owns it).

It is portable – it can be installed on different types of machines.

Main components of UNIX OS: Kernel. Master control program of the

computer. In charge of managing resources and multitasking.

File System. Data is stored in files, which are organized in directories.

Shell. Accepts user commands and passes them on to the Kernel.

Utilities. These are the commands that UNIX understands.

Review: Jobs of an OS

Manage software…. Kernel. Interact with User…. Shell (using

utilities). Control peripherals…. all peripherals are

part of the UNIX File System.

In summary: You type a “utility” into the UNIX Shell, which gets passed to the Kernel for processing.

Your UNIX Account

Since many users share one large disk, each user is given a “piece” of the disk, called an account.

Each part of the disk has permissions associated with it. You will have permission to view only your own files.

In order to work in your account, you will login with a username and password. (to be done before our next class.)

Shell Utilities

% date

% who

% whoami

% mail

% pine

(see chapter 20 of text for more mail details)

% man

The UNIX File System (ch. 6)

The File System is used to organize data. In UNIX, anything from which data can be taken/sent is called a file.ordinary file on diskprinterkeyboard

Ordinary files are either of type:text – each character is stored as its ASCII

value.binary – to be read only by computer.

Directories

A directory in UNIX corresponds to a Folder in Windows (a place on the disk that can hold files and directories).

When you are logged in to your account, you are always in some directory. That is called the current directory.

Your “home” directory is the directory that you are in by default each time you login.

Directory Tree

Directories have a hierarchical structure, represented by a Directory TREE.

root /

bin dev etc home tmp users1

……. sokol …...

root /

bin dev etc home tmp users1

……. sokol …...

courses forms papers

CIS15 CIS23 CIS52

syllabus.htm hmwk1.htm

Pathnames

A pathname is the address of a file or directory. It is the path of the file (or directory) in the Directory Tree.

An absolute pathname is the path from the root to the specified file.

e.g.

/users1/sokol/courses/CIS15/syllabus.htm

/ represents the ROOTNote: in Windows, the backslash \ is used to separate levels of the

tree. All web addressed, i.e. URL’s, use the forward slash as in UNIX.

Relative Pathname

A relative pathname is the path in the directory tree beginning with the “current directory.”

e.g. Suppose I am working in my home directory. I can refer to syllabus.htm as:

courses/CIS15/syllabus.htm

Or, if my current directory is CIS15, I can simply say syllabus.htm

Naming Files and Directories

You do not have to use filename extensions, although you can if you wish.

e.g. notes.txt myprogram.cpp UNIX is CASE SENSITIVE! Do NOT use spaces and special

characters in your filenames (although . _ , are allowed).

Some Shell Commands

pwd prints working (or current) directory cd change directory [without

arguments this brings you to home directory]

ls lists files in current directory

Many commands take options. Example:

ls –la detailed list, and includes hidden files, which are those whose name begins with a . (e.g. .profile, .login)

How can you create a file?

1. Copy or move another file

2. Redirect standard output

3. Use a Text Editor

4. Computer program writes to a file

cp pathname1 pathname2

mv pathname1 pathname2

2. Redirection

You can redirect the output of a command:

e.g. ls > mylist

spell > sperrs

“funnels” the output to a file instead of screen.

> erases file if it exists >> concatenates to end of existing file

3. Text Editor

emacs vi pico

Choose one of these and learn it since you have to be able to type up a text file in UNIX.

4. Computer program

We will cover files in C++ in detail (Chapter 12 of text) so stay tuned…

Permissions

The permissions of each file and directory can be viewed as a sequence of 10 bits.

d stands for directory

r read permission

w write permission

x execute permission

drwxrwxrwxowner group public

Changing Permissions

Your web page has to grant read and execute access to the public.

How can you change permissions?

use the chmod command

examples:

chmod 111001001 public_html

chmod 711 public_html

chmod a=rx mypage.html

chmod a+r mp.html

More shell utilities for File Management cat more less pg lpr rm mkdir rmdir

Pipes

You can send the output of one utility to the input of another utility using |

example:

cat pgm1 | more

who | sort

(note: redirection using > sends to a FILE, piping sends to another command.)

Use the ; to group commands.

example: ls; who; cd

The grep Command

grep will search for a word inside of files or directories. It is extremely useful

examplegrep December pgm1.cpp

[this will list every occurrence of December in the file pgm1.cpp]

OR

grep December pgm*.cpp

[this searches all files that begin with pgm and end with .cpp]

Wildcard character (*)

Other examples of using the *

ls *.cpp // this lists all of your .cpp programs that are in the current directory.

cp *.output outfiles // copies all files ending with .output into a directory called outfiles

Processes (ch 11)

Since UNIX is a multitasking system, a single user can also run several processes at once.

You can either open different windows or you can run a process in the “background.”

For example:

%netscape &

This will open netscape but give you the shell prompt back in your window.

Processes

If you would like to see a list of all your active processes, use the command.

Example:

% ps PID TTY TIME CMD

25157 pts/11 00:00:00 ksh

25177 pts/11 00:00:00 tcsh

25206 pts/11 00:00:00 ps

If you want to terminate a process:

% kill 25177

Processes (cont)

If a process is running in the foreground, and you want to kill it:

^ C (Ctrl+C) To suspend a process, use:

^ Z (Ctrl+Z)

To resume the suspended process:

% fg (for a foreground job)

% bg (for a background job)

Symbols

~

/

.

..

&

*

> >>

|

Programming under UNIX (ch32) 1st level language = machine language (a

binary sequence of 0’s and 1’s) 2nd level language = assembly language

Here, you can use English-like statements to represent machine level instructions.

So, 1 assembly language instruction corresponds to one machine instruction.

3rd level or “High” level languageseasier to programportable

Program Translation

Your high-level language program must be translated into machine language in order for it to be able to run. This is a 3 step process.

1. Preprocessing

2. Compilation

3. Linkage

1. Preprocessing

A preprocessor reads through your program and replaces all preprocessor directives.

A preprocessor directive is any line that begins with a #

e.g. #include <stdlib> Notice that preprocessor directives are

not C++ statements, and therefore do not terminate in a ;

2. Compile

Compiling a program consists of translating a high level language to machine language, called object code.

Object code is NOT executable yet…

To compile your C++ program, type:

% g++ -c mypgm.cpp

or

% CC –c mypgm.cpp

NOTE: the –c option says to only compile.

The CC are capital (lowercase cc is for C).

Compiling in UNIX

When you compile your program, the compilation errors will display on the screen.

You should open your program in a different window to correct the mistakes.

If there are no compilation errors, a file called mypgm.o will be created. This is the object code of your program.

3. Linking

There is still one more step to obtain your executable. It is called “linking.” Linking brings together all library functions that you included, all of your own functions, and your main function and an executable file is created.

% g++ mypgm.o

The same command is used for linking.[You can have linker errors, such as a function that is not

found, or no main function, or multiply defined main’s.]

Running your program

The output of the linker is an executable file called:

a.out

You can check that it has executable permission by typing _________.

To run your program:

% a.out

Output will display on the screen.

% a.out > myoutputfile

Redirects your output to a file.

Compiling and Linking in 1 stepYou can invoke g++ to compile and link

together, but this will be useful only for small programs.

% g++ mypgm.cpp

This will first compile and then link. Errors are labeled either as compiler or as linker errors.