CSE271: Programming in C and the UNIX Environment

Introduction

Prof. Brian D. Davison

Computer Science & Engineering, Lehigh University

Additional Credits

Introductions

• Participants
  • Instructor: Prof. Brian D. Davison
  • Students: undergraduates of varying majors/years
• Why take/teach this course?

Course Objectives

• When this course is complete, you should
  • Know how to program in the C programming language
  • Be comfortable using UNIX
  • Know how to use common C and UNIX development tools
  • Be able to write UNIX shell scripts
  • Be able to write moderate C programs utilizing common UNIX system calls

Course Structure

• Teaching
• Lectures, readings, labs (Wednesdays), homework
• Everything online
  • Course web site, syllabus, assignments, most lecture notes
  • http://www.cse.lehigh.edu/~brian/course/cunix/
  • Slide navigation - just a web page
• Evaluation
• Two hourly exams (10%+10%), one final exam (20%), programming (40%), homework, weekly quizzes, class participation (20%)

Course Materials

• Required Textbooks
• Harley Hahn's Guide to Unix and Linux, by Hahn (McGraw-Hill, 2009)
• Understanding Unix/Linux Programming: A Guide to Theory and Practice, by Molay (Prentice Hall, 2003)
• Plus a book on C
• C Primer Plus, 5th Ed., by Prata (SAMS, 2005) RECOMMENDED
• C: A Reference Manual, 5th Ed., by Harbison and Steele (Prentice Hall, 2002)
• Online Sources
• Many additional tutorials, textbooks, FAQs, etc.
• In-class Information
• You are responsible for everything we do in class.

Importance

• Why is UNIX important to know?
• Why is C important to know?

Why is UNIX important to know?

• Much of the Internet (routers, web servers, dns servers, etc.) runs UNIX, and much of the original Internet infrastructure was developed under UNIX
• Many UNIX apps and UNIX-like OSes are free and/or open source
• UNIX is
  • An OS that is inherently multi-process and multi-user
  • A powerful, scalable, efficient networked OS that runs on a variety of hardware
  • Often used in high-end workstations, supercomputers, and government and large business computing centers
  • Protected -- users can't access others' files, the death of one process generally does not kill the machine, etc.
  • An example of good software design tested by decades of use
• UNIX usually also includes the X-Window System, a powerful windowing paradigm

UNIX Maturation

• UNIX started out as an educational and research system
• UNIX (and UNIX-like OSes) have become a universal operating system
• Now found in
  • embedded systems (parking meters, digital video recorders, wristwatches, in-flight entertainment systems)
  • Mac laptops and desktops
  • almost all cell phones and tablets
  • millions of web servers
  • cheap desktop systems sold by Walmart, etc.
• It has grown much beyond its original design 30+ years ago

UNIX Philosophy

• Doug McIlroy
  • Write programs that do one thing and do it well
  • Write programs to work together
  • Write programs to handle text streams, because that is a universal interface
• Unattributed

  "The UNIX philosophy basically involves giving you enough rope to hang yourself. And then a couple of feet more, just to be sure."

UNIX Philosophy, continued

• Use "filters" - small programs that do one thing and can be combined with other small programs
• Give users as much control as possible without allowing them to affect other users
• Use common interfaces
  • Devices, sockets, files all the same
  • All data can be represented as character sequences
• Simplicity is more important than efficiency or featurism

UNIX Interfaces

• GUI or command line?
• GUI is great (easy) but often changes with later releases
• GUI requires graphics/mouse (obvious, but not always available)
• Every UNIX system has a command line interface
• The command line is (mostly) the same from version to version
• The command line can easily run multiple programs and be scripted

Why is C important to know?

• UNIX was written in C, and most UNIX development is in C
• Sometimes called "easy to learn but difficult to master"
• C is programmer efficient -- code can be written briefly
• C is flexible and provides lots of developer control over details, making it ideal when you need operational speed and resource efficiency
• C code correlates highly with assembly, making it easier to understand what is really going on
• Many 'programmers' cannot program in C, making you more valuable. :-)
• C code is usually faster than anything else
• Nearly everything offers a C library

The C Programming Language

• is weakly typed
  • You can read data from memory as any type you like
• is staticly typed
  • Types are only checked at compile-time
• is structured
  • Structures are used to control the flow of execution (e.g., while, for, if/then)
• is procedural
  • C++ is mostly a superset of C that adds object oriented functionality.
• is low-level
  • C can directly access structures that are tied to hardware

History of C

• The B language was created by Ken Thompson in 1969-1970, as a derivation of BCPL.
• Dennis Ritchie turned B into C during 1971-73, keeping most of B's syntax while adding types as well as other changes.
• The (still new) UNIX OS was re-implemented in C in 1972-1974.
• Kernighan and Ritchie publish The C Programming Language, defining the 'original' K&R C in 1978.
• Bjarne Stroustrup invents C++ in 1983-1985.
• ANSI C published in 1990.
• Revisions adopted in 1999 (ANSI C99).

The spirit of C

• The spirit of C (as summarized by a C standards committee):
• Trust the programmer.
• Don't prevent the programmer from doing what needs to be done.
• Keep the language small and simple.
• Provide only one way to do an operation.
• Make it fast, even if it is not guaranteed to be portable.

Homework

• Homework 0 is on the course website, and is due Wednesday.
• Use ssh to log into a Sun.
• Lehigh students can get a number of ssh-compatible implementations for various operating systems.
• If you have forgotten your CSE/ECE Sun account password, or don't yet have an account, send mail to help (at) cse.lehigh.edu from your Lehigh account (e.g., via imp)

Hello World

• Use an editor to create hello.c
• Compile using gcc hello.c
• Assuming no compilation or linking errors, run using ./a.out
• If no runtime errors, the program will output its greeting and finish.
• In lab on Wednesday we will continue with:
  • Using the X-Window system
  • Intro to using UNIX