Transcript Document

Lab 2
Advanced Operating System
Spring 2013
Advanced Operating System Spring 2013 - Lab 2
Shell Scripting
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Today Objectives
• Review on Shell interpreter
• Know cons and pros of shell scripting
Advanced Operating System Spring 2013 - Lab 2
• Know basic shell scripting (Tcl)
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Shell (review)
Advanced Operating System Spring 2013 - Lab 2
• Is a utility program with the Linux system that serves as an interface
between the user and the kernel
• Plays an important role of command interpretation for the kernel
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Remember: How the
Shell works?
Shell (review) … cont.
Advanced Operating System Spring 2013 - Lab 2
• The shell as a Command Interpreter :
• Reads the command
• Locates the file in the directories containing utilities
• Loads the utility into memory
• Executes the utility
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•
The shell creates a child shell for the execution of a utility
•
The shell requests the kernel for any hardware interaction
Advanced Operating System Spring 2013 - Lab 2
Shell (review) … cont.
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Unix Shell
• There are many shells , some of them are
this shell
• C Shell (csh/tcsh ): csh is the executable filename for this
shell
• Korn Shell: The executable filename is ksh
• Restricted Shell: Is typically used for guest logins
• To know the Type of your Shell write “echo $SHELL”
• The command to change your shell is ……… ?!
Advanced Operating System Spring 2013 - Lab 2
• Bourne Shell (sh/bash): sh is the executable filename for
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Shell Scripts
• Stores a sequence of frequently used Linux commands in a file
• Enables the shell to read the file and execute the commands in it
constructs that make programming possible
Advanced Operating System Spring 2013 - Lab 2
• Allows manipulation of variables, flow-of-control and iteration
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Hello World Example
#!/bin/tclsh
# My first script
Directory for the shell that will interpret the script
Comment 
puts "Hello World!”
• To run the script save it with any name (i.e. hello)
• Give it execute permission (chmod …)
• Then run it (i.e. ./hello)
Hint : to know the path to your shell write on the shell
which shellname (i.e. which tclsh)
Advanced Operating System Spring 2013 - Lab 2
Commands …..
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Exercise 1 ... (7 mins )
• Open server.c and client.c , take 2 mins to understand what they do
• Check the IPC resources used (ipcs ..)
• take notes how many message queues there
• Run the client program
• Enter the following three messages separately
(message1 , message2 , message3)
• Repeat last 2 steps
• What happened ? And why ?
• Remove message queues (ipcrm)
Advanced Operating System Spring 2013 - Lab 2
• Run server program in the background ( … &)
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Exercise 1 ... cont.
Don't you think a quick script could make our life easier :)
Advanced Operating System Spring 2013 - Lab 2
• Imagine that you repeat this task every time you run your
program or your program crashes ….
Boring and Timing Consuming isn’t it !!
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• A working knowledge of shell scripting is essential to
understand the behavior of your system .
 Consider that as a Linux machine boots up, it executes
the shell scripts in /etc/rc.d to restore the system configuration
and set up services.
• Writing shell scripts is easy to learn, simple to make , easier to
debug and faster (no compilation, write and run ).
• A shell script is a "quick and dirty" method of prototyping a
complex application.
• Whenever you find yourself doing the same task over and over
again you should use shell scripting
Advanced Operating System Spring 2013 - Lab 2
So Why Script Programming?
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• Scripting language like any other language, it has
 Conditional statements (if …)
 Loops (for , while , until , …)
 Functions
 Variables
 Can do arithmetic operation
 Very easy string handling
 ...etc
• As mentioned before it is much easier to learn , to use to debug but
Take Care all comes at a cost
• Scripts are interpreted while normal language are pre-compiled which
make them much more faster
• Also Scripts in general doesn't have such structures
• A good reference for bash scripting is http://tldp.org/HOWTO/BashProg-Intro-HOWTO.html
Advanced Operating System Spring 2013 - Lab 2
Scripting Language
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Tcl (Tool Command Interpreter)
• Extensible
You can easily add new commands and libraries to a Tcl interpreter.
• Orthogonal
The syntax is simple and consistent - Tcl code is easy to write and also easy to read.
• Modern
All the modern programming constructs are supported, including simple objects and
namespaces.
• Multiplatform
The Tcl interpreter has been ported to more platforms that Java. The same scripts can
be run on everything from IBM Big-Iron to real-time embedded kernels.
• Powerful
The Tcl architects have provided powerful and well-thought generalizations that make
it fast and easy to write what would otherwise be complex applications.
Advanced Operating System Spring 2013 - Lab 2
• Embeddable
You can use Tcl as a scripting language within another larger application.
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Basic operations
• print to screen (puts)
puts –nonewline "Hello, world!"
puts "!!"
set income 32000
puts "income is $income"
(using '$' to get the value of a variable)
• mathematical expressions (expr)
set a 10.0
expr $a + 5
expr int($a/3)
Advanced Operating System Spring 2013 - Lab 2
• assignment (set)
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Some useful commands
• unset: destroy a variable
unset num
if {![info exists num]} {
set num 0
}
incr num
Advanced Operating System Spring 2013 - Lab 2
• info: check whether the named variable has been defined
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# : single-line comments, similar to "//" in C
;# : in-line comments, just like "//" in C
\ : escape character, same function as in C
: also used to break a long line of code to two lines
$ : get the value of a variable
• var : name of variable
• $var : value of variable
[] : evaluate command inside brackets
Advanced Operating System Spring 2013 - Lab 2
Special characters
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Control structures (1)
set income 32000
if {$income > 30000} {
puts "$income -- high"
} elseif {$income > 20000} {
puts "$income -- middle"
} else {
puts "$income -- low"
}
• while loops
set i 0
while {$i < 100} {
puts "I am at count $i"
incr i
}
Advanced Operating System Spring 2013 - Lab 2
• if then else
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Control structures (2)
• for loops
for {set i 0} {$i < 100} {incr i} {
puts "I am at count $i and going up"
for {set i 100} {$i > 0} {set i [expr $i - 1]} {
puts "I am at count $i and going down"
}
• foreach loops
set lstColors {red orange yellow green blue purple}
foreach c $lstColors {
puts $c
}
Advanced Operating System Spring 2013 - Lab 2
}
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Control structures (3)
• foreach loops (con't)
set lstFoods {apple orange banana lime berry grape}
foreach f $lstFoods c $lstColors {
puts "a $f is usually $c"
}
foreach {a b} $lstFoods c $lstColors {
puts "$a & $b are foods. $c is a color."
}
Advanced Operating System Spring 2013 - Lab 2
set lstColors {red orange yellow green blue purple}
foreach {a b c} $lstColors {
puts "$c--$b--$a"
}
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Procedures(1)
• procedure calls (embedded commands)
set b [expr $a + 5]
puts "The value of b is $b"
proc foo {a b c} {
return [expr $a * $b - $c]
}
puts [expr [foo 2 3 4] + 5]
proc bar { } {
puts "I'm in the bar procedure"
}
bar
Advanced Operating System Spring 2013 - Lab 2
• create your own procedure (called by value only)
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Procedures (2)
• procedure calls (variable number of arguments)
proc sum {args} {
set s 0
foreach arg $args {
}
return $s
}
puts [sum 1 2 3 4]
puts [sum 1 2]
puts [sum 4]
Advanced Operating System Spring 2013 - Lab 2
incr s $arg
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Procedures (3)
• procedure calls (implicit variable)
proc power {a {b 2}} {
if {$b == 2} {
}
set value 1
for {set i 0} {$i<$b} {incr i} {
set value [expr $value * $a]
}
return $value
}
set v1 [power 5]
set v2 [power 5 4]
puts "5^2 is $v1"
puts "5^4 is $v2"
Advanced Operating System Spring 2013 - Lab 2
return [expr $a * $a]
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Variable scope
set a 5
set b 6
set c 7
proc var_scope { } {
global a
set a 3
set b 2
set ::c 1
}
var_scope
puts "The value for a b c is: $a $b $c"
Advanced Operating System Spring 2013 - Lab 2
local and global variables
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Variable scope
set a 5
set b 6
set c 7
proc var_scope { } {
upvar a x
set x 3
set b 2
set ::c 1
}
var_scope
puts "The value for a b c is: $a $b $c"
Advanced Operating System Spring 2013 - Lab 2
local and global variables
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Exercise 2 ... (30 min)
proc change {n args} {...}
Examples :
change 75 25 10 5 1
=> 3 0 0 0
change 75 10 25 1 5
=> 3 0 0 0
change 75 50 25 10 5 1
=> 1 1 0 0 0
Advanced Operating System Spring 2013 - Lab 2
1. Write the function change, which takes a whole number and set of coins (integer numbers too) as its arguments and
prints a list that represents how to "make change" for that number using the set of coins (or notes) for any decimal
currency. first number is the whole number then followed by the set of coins . your function should have the minimum
number of coins possible . (10 mins)
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Exercise 2 ...
2. Write the command vardefault, which takes two arguments, the name of a variable, and a default value. If the
variable is defined in the calling scope, vardefault returns the variable's value. If it is not defined, vardefault
returns the default value. (10 min)
Examples :
set x 45
vardefault x 0
=> 45
proc foo {} {
Vardefault x 0
}
foo
=> 0
To write this function, you'll need to use upvar to achieve call by name, and you'll need a way to test
whether or not a variable is defined (use info exists).
Advanced Operating System Spring 2013 - Lab 2
proc vardefault {var default} {...}
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Exercise 2 ...
3. Write the iota function, which takes a numeric argument n and returns a list of numbers of length n which are
the numbers from 0 to n-1. the iota function can take an optional second argument which is an increment to
separate the integer values. The default increment is 1. iota always returns a list whose length is equal to its first
argument. (10 min)
Examples :
iota 10
=> 0 1 2 3 4 5 6 7 8 9
iota 10 3
0 3 6 9 12 15 18 21 24 27
Advanced Operating System Spring 2013 - Lab 2
proc iota {n {inc 1}} {...}
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Exercise 2 …. (optional)
proc bits {howmany num} {...}
Examples
bits 0777
 111111111
bits 0644
 110100100
Advanced Operating System Spring 2013 - Lab 2
4. Write the function bits which takes two parameters, both numbers, and returns a binary representation of
the first number as a list of bits (each bit is a 0 or a 1), from most significant at the left to least siginifcant
at the right. The result list should contain as many bits as specified by the second number, which should
be an optional parameter, using leading zero bits if necessary (assume that the bit length requested is
long enough to represent the number). If the second parameter isn't specified, use the minimal number of
bits (no leading zeros).
You'll probably want to use the expr command's bit-fiddling operators for this.
bits 19
 10011
bits 1 3
 001
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Lists in Tcl
• Everything is a list!
• Many ways to create a list
set myList [list $a $b $c]
set myList {$a $b $c}
set myList [list a
set myList "a
b
set s Hello
puts "The length
=> The length of
puts {The length
=> The length of
b
c"
of $s
Hello
of $s
$s is
c]
is [string length $s]."
is 5.
is [string length $s].}
[string length $s].
Advanced Operating System Spring 2013 - Lab 2
set myList [list a b c]
set myList "a b c"
set myList {a b c}
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List operations
Advanced Operating System Spring 2013 - Lab 2
set lstStudents [list "Fan" "Kristy" "Susan"]
puts [lindex $lstStudents 0]
puts [lindex $lstStudents end]
puts [llength lstStudents] (unexpected result!)
puts [llength $lstStudents]
lappend $lstStudents "Peter" (wrong!)
lappend lstStudents "Peter"
puts [linsert lstStudents 2 "Tom"] (wrong!)
puts [linsert $lstStudents 2 "Tom"]
set lstStudents [linsert $lstStudents 2 "Tom"]
set lstStudents [lreplace $lstStudents 3 3 "Rachel"]
set lstStudents [lreplace $lstStudents end end]
set lstStudents [lsort –ascii $lstStudents]
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puts [lsearch $lstStudents "Peter"]
set a [list [list x y z]]
puts [lindex $a 0]
puts [lindex [lindex $a 0] 1]
puts [lindex [lindex $a 1] 0] (unexpected result)
set a [list x [list [list y] [list z]]]
=> How to get to the z?
set arg1 [list g [list f [list h [list i X]]] [list r Y] k]
set arg2 [list g [list f [list h [list i Y]]] [list r b] L]
set both [list $arg1 $arg2]
puts $both
Advanced Operating System Spring 2013 - Lab 2
Lists of lists (of lists…)
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Array operations
set color(rose) red
set color(sky) blue
set color(medal) gold
set color(leaves) green
set color(blackboard) black
puts [array exists color]
(tests if an array with the name "color" exists)
puts [array exists colour]
puts [array names color] (returns a list of the index strings)
foreach item [array names color] {
puts "$item is $color($item)"
}
(iterating through array)
set lstColor [array get color] (convert array to list)
array set color $lstColor
(convert list to array)
Advanced Operating System Spring 2013 - Lab 2
Associative arrays (string as index)
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Regular expressions
set stmt "Fan is one of Shania’s fans"
regsub –nocase "fan" $stmt "Kristy" newStmt
?switches? exp string subSpec ?varName?
puts "$newStmt"
regsub –nocase –all "fan" $stmt "Kristy" newStmt
puts "$newStmt"
• regexp
(returns 1 if the regular expression matches the string, else returns 0)
puts [regexp –nocase "fan" $stmt]
?switches? regexp string
• format
Advanced Operating System Spring 2013 - Lab 2
• regsub
puts [format "%s is a %d-year-old" Fan 26]
formatString
?arg arg ...?
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set statement "
Fan is a student
"
set statement [string trim $statement]
puts [string length $statement]
puts [string length statement]
puts [string index $statement 4]
puts [string index $statement end]
puts [string first "is" $statement]
(string last)
puts [string first $statement "is"]
puts [string range $statement 4 end]
puts [string replace $statement 9 end "professor"]
puts [string match "*student" $statement] (* ? [])
Advanced Operating System Spring 2013 - Lab 2
String operations
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File operations
################ source.txt ################
Fan is a CSE student.
Fan is also one of Shania’s fans.
Kristy and Fan are classmates.
Advanced Operating System Spring 2013 - Lab 2
set fRead [open source.txt r]
set fWrite [open target.txt w]
while {![eof $fRead]} {
set strLine [gets $fRead] ;#or gets $fRead strLine
regsub –nocase –all "fan" $strLine "kristy" strLine
puts $fWrite $strLine
}
close $fRead
close $fWrite
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Miscellaneous commands
• eval: execute a command dynamically built up in your
program
set Number1 17
set Number2 25
set Result [expr $Number1 + $Number2]
}
eval $Script
• exec: execute external programs
Advanced Operating System Spring 2013 - Lab 2
set Script {
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Common pitfalls
a b {} d
Advanced Operating System Spring 2013 - Lab 2
• Missing $ or extraneous $
• Using {a} vs "a" vs [list a]
• Creating list items that are empty lists
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•
•
•
•
•
need data structures, such as linked lists or trees
need to generate or manipulate graphics or GUIs
need direct access to system hardware.
procedures involving heavy-duty math operations.
resource-intensive tasks, especially where speed is a factor
(sorting, hashing, etc.)
• complex applications, where structured programming is a
necessity (need typechecking of variables, function prototypes,
etc.)
• situations where security is important
Advanced Operating System Spring 2013 - Lab 2
When not to use shell scripts
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Exercise 3 …. (60 min)
1. Write the function strlenlist, which takes one argument, a list of strings, and returns a list of equal length
as a result, in which each element is the string length of the corresponding element of the argument list.
(10 mins )
proc strlenlist {L} {...}
strlenlist {34 987 1 567 -23 8}
=> 2 3 1 3 3 1
strlenlist {foo bar antidisestablishmentarianism}
=> 3 3 28
Advanced Operating System Spring 2013 - Lab 2
Examples :
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Exercise 3 …. (60 min)
proc choose {trues falses bools} {...}
Examples :
choose [list a b c d] [list A B C D] [list 0 1 1 0]
=> A b c D
Advanced Operating System Spring 2013 - Lab 2
2. Write the function choose, which takes three parameters: three equal-length lists, the first two of arbitrary
values, and the third a list of boolean values (zeros and ones). choose returns a list (also of the same
length) where each element is chosen from one of the first two lists, depending on the corresponding
boolean value. Elements of the first parameter are chosen for 1's (true), while elements of the second
parameter are chosen for 0's (false). choose is one of many useful functions that operate on bit vectors.
(10 mins )
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Exercise 3 …. (60 min)
3. Write a function to find all lines containing a certain word in a file . It takes filename and the word to
search for as an argument , and returns line number : the line this word occurs at
Examples :
################ source.txt ################
Fan is a CSE student.
Fan is also one of Shania’s fans.
Kristy and Fan are classmates.
findword source.txt is
 1 : Fan is a CSE student
 2 : Fan is also on of Shania’s fans.
Advanced Operating System Spring 2013 - Lab 2
proc findword { filename word} { …}
(Hint : it could be done with one line of code  )
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Exercise 3 …. (60 min)
The first line will contain the first string, of between 1 and 10 characters, using lower case letters. The second line
will contain the second string, again between 1 and 10 lower case letters. The third line will be a single integer i (1
<= i <= 2^30). Please note that there can be any number of sets of input, each consisting of the specified three
lines of input.
Sample input
fibonacci
revenge
1000000
Advanced Operating System Spring 2013 - Lab 2
A sequence of strings is generated as follows: the first two strings are given and each successive string is made by
joining together the previous two strings (in their original order). For example, if the first string is abc and the
second string is cde, the third string will be abccde and the fourth will be cdeabccde. The task for this question is
to determine the ith character in the sequence of strings (not the ith string). In the previous example the 2nd
character is b, the 5th is d, as is the 11th. The 13th character, which happens to be the 1st character of the 4th
term, is c. (bonus)
Input
Output
Output the ith character in each input sequence, separated by lines.
Sample output
e
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Tcl references and resources
• Help file
http://www.tcl.tk/scripting/
http://www.msen.com/~clif/TclTutor.html
• Search site:
• List of Tcl commands with man pages
http://tcl.activestate.com/man/tcl8.4/TclCmd/contents.htm
• Tcl examples:
http://www.beedub.com/book/2nd/tclintro.doc.html#2668
• All code in this tutorial (plus some) and expected output
ftp://cslu.ece.ogi.edu/pub/kristina/
tutorial.tcl, tutorial_output.txt, source.txt
Advanced Operating System Spring 2013 - Lab 2
http://xyresix.com/nwsbook/search.html
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Tcl editors
Any editor
nedit
emacs
TextPad
• http://www.textpad.com/
• http://www.textpad.com/add-ons/synn2t.html - TCL/TK (5)
Advanced Operating System Spring 2013 - Lab 2
•
•
•
•
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• Linux Shell Scripting Tutorial - A Beginner's handbook - Vivek G.
Gite
• Advanced Bash-Scripting Guide: A complete guide to shell
scripting, using Bash by Mendel Cooper
• CSCI6303 – Principles of I.T.
• http://tmml.sourceforge.net/doc/tcl/
• http://en.wikipedia.org/wiki/Tcl
Advanced Operating System Spring 2013 - Lab 2
Other References
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