Shells Scripts

1
Shells Scripts
COMP 121-401 UNIX Programming

• Andrew Nashel
• nashel_at_cs.unc.edu
• Department of Computer Science
• February 6, 2004

2
Course topics

• Shell scripts
• Homework

3
Shells scripts

• Any collection of shell commands can be stored in
  a file called a shell script. Scripts have
  variables and flow control statements like other
  programming languages.
• There are two popular classes of shells
• C shell (csh) and variants (tcsh)
• Bourne shell (sh) and variants (bash, ksh)

4
Invoking scripts

• There are two ways to launch scripts
• 1) Direct interpretation
• csh scriptfile args
• 2) Indirect interpretation
• The first line of the file must be
• !/bin/csh
• and the file must be executable.

C Shell
5
Variables

• To set variables
• set X value
• Variable contents are accessed using
• echo PATH
• To count the number of variable elements
• echo Y

C Shell
6
Variables contd

• To create lists
• set Y (abc 1 123)
• To set a list element
• set Y2 3
• To view a list element
• echo Y2

C Shell
7
Command arguments

• A shell script to swap files
• ! /bin/csh f
• set tmp argv1
• cp argv2 argv1
• cp tmp argv2
• The number of arguments to a script
• argv

C Shell
8
if-then-else

• if ( expr ) simple-command
• if ( expr ) then
• commandlist-1
• else
• commandlist-2
• endif

C Shell
9
if-then-else contd

• An example
• if (argv 2) then
• echo we need two parameters!
• else
• set name1 argv1
• set name2 argv2
• endif

C Shell
10
Loops

• while ( expr )
• commandlist
• end
• foreach var ( worddlist )
• commandlist
• end

C Shell
11
switch

• switch ( str )
• case string1
• commandlist1
• breaksw
• case string2
• commandlist2
• breaksw
• default
• commandlist
• endsw

C Shell
12
goto (Considered harmful!)

• To jump unconditionally
• goto label
• A label is a line such as
• label
• The classic paper on why not to use goto
• Go To Statement Considered HarmfulEdsger W.
  Dijkstra, CACM, March 1968

C Shell
13
An example script

• ! /bin/csh -f
• foreach name (argv)
• if ( -f name ) then
• echo -n "delete the file 'name' (y/n/q)?"
• else
• echo -n "delete the entire dir 'name'
  (y/n/q)? "
  
• endif
• set ans
• switch (ans)
• case n continue
• case q exit
• case y rm -r name continue
• endsw
• end

C Shell
14
Homework

• Due Monday
• Write a shell script that reads a file and
  replaces a particular text string with another,
  all input given interactively.
  
• Hint Use sed for text replacement.
• This is your final graded assignment!

15
Homework contd

• Example
• ./myscript
• File to read news.txt
• Search text Duke
• Replacement text Dookie
• Dookie University
• Department of Mathematics
• Weekly Calendar

16
Hmmmm.

• Okay, shell scripts are useful, but a little
  boring.

17
Unix Games!
COMP 121-401 UNIX Programming

• Andrew Nashel
• nashel_at_cs.unc.edu
• Department of Computer Science
• February 6, 2004

18
SpaceWar

• SpaceWar may be the most important computer game
  ever. The first version was developed for the
  PDP-1 at MIT in 1960. The game has been under
  essentially constant development since.

19
SpaceWar contd

• The first CRT display was a converted
  oscilloscope used to play SpaceWar. The first
  trackball (and thus, the first mouse) was a
  SpaceWar control at MIT. It is said that Ken
  Thompson salvaged a PDP-1 and created a new
  operating system, now called UNIX, so that he
  could play SpaceWar.

20
Spacewar contd
The PDP-1
Real 133 gamers
21
Nethack

• A Rogue-like classic dungeon crawl game retrieve
  the Amulet of Yendor!

22
XPilot

• The classic multiplayer 2D shooter.

23
XBill

• Whack the computer hacker and free the computers
  from the awful virus!

24
Xmame

• Multiple Arcade Machine Emulator

25
Xconq

• A general purpose strategy game.

26
Tux Racer

• Be the penguin.

27
Freeciv
28
FlightGear
29
BZFlag
30
UNC Games!
COMP 121-401 UNIX Programming

• Andrew Nashel
• nashel_at_cs.unc.edu
• Department of Computer Science
• February 6, 2004

31
Adventure

• Warren Robinett, a former UNC-CS professor, wrote
  Adventure, the first action-adventure video game,
  in 1978 and it sold over 1 million copies.

He also founded The Learning Company for
educational software.
It included the first easter egg!
32
Ratchet and Clank

• Max Garber, UNC 02, works at Insomnic Games, Los
  Angeles

33
Buffy and Wrath

• Stephan Sherman and Vince Scheib, 02 work for
  The Collective in Newport Beach, CA

34
Midnight Club 2

• Andrew Zaferakis, UNC 02, works for Rockstar San
  Diego

35
Vicious Cycle

• Greg Coombe wont ever graduate.