SPR720

UNIX Shell Programming(Scripting with BASH)

Instructor: Murray Saul

Agenda Overview of SPR720

Discuss Course Outline Evaluation Class Standards / Required Materials

Purpose of an Operating System (OS)

History Unix / Linux OS Characteristics of Unix / Linux OS

How to Contact Instructor

Room #: T2105

Telephone #:(416) 491-5050 x 3336

E-mail:murray.saul@senecac.on.ca

Instructor’s Website: http://cs.senecac.on.ca/~murray.saul

Class Standards(See Instructor’s Website)

Evaluation Attendance / Participation Late Assignments Missed Tests Missed Final Exam Things that Annoy Instructor Cheating / Plagiarism

Required Text A Practical Guide to Linux, by Mark

Sobell. Publisher: Addison-Wesley;ISBN 0-201-89549-8.

Attention These PowerPoint notes are based

on Chapter 1 of textbook “A Practical Guide to Linux”

Read pages 3 to 17

Definition of an Operating System (OS)

An operating system is a control program for a computer that performs the following operations: allocates computer resources schedules routine tasks provides a platform to run application

software for users to accomplish tasks provides an interface between the

user & the computer

History of Unix OS Prior to Unix, many operating systems ran

collections or “batches” of operations one at a time.

This single-user “batch-processing” approach did not take advantage of the potential processing power and speed of computers

Enter data infiles to be later

processed

ProcessCollection or

“Batch” of files

Receiveinformation of processed data

Note: batch processing lacks the advantage of immediate feedback as opposed to online processing

History of Unix OS The Unix OS was developed (based on

Multics & CTSS operating systems) by Ken Thompson at the AT&T Bell Laboratories in 1969. He wanted to create an multi-user operating system to run “space wars” game.

Ken’s philosophy was to create an operating system with commands or “utilities” that would do one thing well (i.e. UNIX). Pipes could be used combine commands...

History of Unix OS The first versions of UNIX were written

in “machine-dependent” program (such as PDP-7).

Ken Thompson approach Dennis Ritchie developer of C program), and in 1973 they compiled UNIX in C programming language to make operating system “portable” to other computers systems.

History of Unix

Ken Thompson (recently retired from Bell Labs) is on left, and Dennis Ritchie is in the middle. “What’s his name” is on the right…

UNIX Features The Unix OS is a multi-user OS allowing

more that more person to directly communicate with the computer.

Although the OS can only work on one task at a time, a small piece of time (time slice) is dedicated to each task or user - this is referred to as “time-sharing”.

Time sharing gives the illusion that the CPU is giving all the users its full attention

Illustration of Time-Sharing

TIME

User 1

User 2

User 3

User 4User 5

User 6

User 7

User 8

Development of Unix OS Unix became a popular OS among

institutions such as colleges & universities through a 4-year “try before you buy” deal.

Efficient and inexpensive way of networking promotes Internet use and file-sharing Open system allows for source code to be

shared among many programmers - allows for better coordination among programmers

Development of Unix OS Students at University of California

(in Berkley) further developed the UNIX operating system and introduced the BDS version of Unix

Unix

Bell LabsUNIX System V (5)Proprietary

Berkley Software Distribution (BSD)Free

Development of Unix OS There were versions of UNIX for

the Personal Computer (PC), such as XENIX, etc., but they didn’t catch on in popularity until Linux was developed in the early 90’s.

History of Linux Linux operating

system developed by programming student Linus Torvalds

Linus wanted to develop Unix-like OS just to experiment with new 386 computer at the time...

Why Has Linux Become soPopular?

Linus decided to make Linux OSsource-code for Linux Kernal open to all:

Unlike traditional Operating Systems, anyone can modify and distribute Linux OS (as long as they distribute source code of Linux Kernel)

“Competition among Hackers” allow code to be improved and distributed often

Many users can spot bugs in the operating system or application if source code is “open”

Why Has Linux Become soPopular?

Other Factors: PC’s have increased processing power and a

there has been a noted shift from mainframes and minicomputers to PCs.

Since Linux is a “Unix Work-alike”, this OS has a reputation to be a very stable platform for networking (creating at-home servers) and running / maintaining applications.

Agencies such as Free Software Foundation created GNU project to provide free software.

Concerns Some people claim that “there are as

many version of Linux as there are users…”

POSIX (Portable Operating System Interface for Computer Environments) is a government standard to ensure consistency among different UNIX and Linux versions.

Many versions of Linux are approaching POSIX standard.

Concerns Freedom of allowing Linux users to create

“servers” connected up to Internet can lead to attacks from experienced hackers.

Linux commands may be considered “user-unfriendly” although GUIs are now used.

Prior reputation for difficult install process including the loss of data on other hard disk partitions.