Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

UNIX Shell Script Programming

Tutor Session III:

Wongyos Keardsri (P’Bank)Department of Computer EngineeringFaculty of Engineering, Chulalongkorn UniversityBangkok, Thailand

Mobile Phone: 089-5993490E-mail: wongyos@gmail.com, MSN: bankberrer@hotmail.comTwitter: @wongyos

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Tutor Outline

Introduction to ShellShellShell Script

VariablesCreating/AssigningAccessingSetting

Getting Start Shell ScriptInclude shellCreate shellRun shell

Data OperationsDecision Statements

If-elseSwitch-case

Iteration StatementForWhile

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Introduction to Shell

What is the shell or Unix shell?A command-line interpreter and script host that provides a traditional user interface for the Unixoperating system and for Unix-like systemsThere are many shells; sh, bash, ksh, csh, zsh, …

Bourne Shell (sh)Written by Stephen BourneWas the 1st popular Unix shell

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Bourne Shell (sh) (Cont)Available on all Unix systemsSupports a fairly versatile programming languageA subset of more powerful Korn shell (ksh)Implement with regular C programmingExecutable file is stored as /bin/sh

(Cont)

Introduction to Shell

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Variables

Creating and assigning a variable

Printing/Showing a variable value

Setting environment variable

Read only variable

name=valuename=value

echo $name

export NAME

No spacesNo spaces

With spacesWith spaces

readonly name

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Variables

Example$ age=15$ nickname=Bank$ echo I'm $nickname, $age years old

More an examples by yourself

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Variables

Accessing a variable

(Cont)

Syntax Action $name Replaced by the value of name.

${name} Replaced by the value of name.

${name-word} Replaced by the value of name if set, and word otherwise.

${name+word} Replaced by word if name is set, and nothing otherwise.

${name=word} Assign word to the variable name if name is not already set and then replaced by the value of name.

${name?word} Replaced by name if name is set. If name is not set, word is displayed to the standard error and the shell is exited.

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Variables

Example

(Cont)

$ verb=sing$ echo I like $verbingI like$ echo I like ${verb}ingI like singing

More an examples by yourself

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Getting Start Shell Script

What is the shell script?Similar to DOS batch filesQuick and simple programmingText file interpreted by shell, effectively new commandList of shell commands to be run sequentiallyTypical operations for file manipulation, program execution, and printing text

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Getting Start Shell Script

Include full path to interpreter (shell)

Example

(Cont)

#!/path/shell

#!/bin/sh#!/usr/bin/sh#!/bin/csh -f

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Getting Start Shell Script

Using vi command to create shell script fileRunning shell script by using the command below

Example

(Cont)

sh [file]

$ vi test.sh...$ sh test.sh

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Getting Start Shell Script

Interaction with userOutput value

Input value

Comment line

(Cont)

echo [texts/variables]

read [variables]

# your comments

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Getting Start Shell Script(Cont)

Getting Start Shell Script(Cont)

Special Variables$# Number of arguments on command line$0 Name that script was called as$1-$9 Command line arguments$* All arguments$@ All arguments (separately quoted)$? Numeric result code of previous command$$ Process ID of this running script

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Example$ cat example1.shecho there are $# command line arguments: $@$ sh example1.shthere are 0 command line arguments:$ sh example1.sh x y zthere are 3 command line arguments: x y z

More an examples by yourself

Getting Start Shell Script(Cont)

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Data Operation

Operators

Using expr to excute operators

Operators Meaning* / % multiplication, division, remainder+ - addition, subtraction= != > < >= <= comparison operators& logical and| logical or

expr $va1 op $var2

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Data Operation

Conditional Expressions

test returns a zero exit code if expression evaluates to true; otherwise, nonzero exit status

test forms-d filename True if filname exists as a directory file-f filename True if filname exists as a nondirectory file-l string True if length of string is nonzero-n string True if string contains at least one character

(Cont)

test [expression]

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Data Operation

test forms (Cont)-r filename True if filname exists as a readable file-w filename True if filname exists as a writable file-x filename True if filname exists as an executable file-z string True if string contains no charactersstr1 = str2 True if str1 is equal to str2str1 != str2 True if str1 is not equal to str2string True if string is not nullint1 -eq int2 True if int1 is equal to int2int1 -ne int2 True if int1 is not equal to int2int1 -gt int2 True if int1 is greater than int2

(Cont)

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Data Operation

test forms (Cont)int1 -ge int2 True if int1 is greater than or equal to int2int1 -lt int2 True if int1 is less than int2int1 -le int2 True if int1 is less than or equalt to int2!expr True if expr is falseexpr1 -a expr2 True if ezpr1 and expr2 are trueexpr1 -o expr2 True if ezpr1 or expr2 are true

(Cont)

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Decision Statement

If-else statement

if [condition]then [result]

elif [condition]then [result]

else[result]

fi

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Decision Statement

Exampleif test -r file1

then echo "file1"elif [ -r file2 ]

then cp file2 file3echo "file2 copy to file3"

elseecho "no file"

fiMore the examples by yourself

test –r file2

(Cont)

test –r file2

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Decision Statement

Switch-case statement

case $var invalue1) [result] ;;value2) [result] ;;...*) [result] ;;

esac Default case

(Cont)

Default case

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Decision Statement

Examplecase $day in

Monday ) echo "A new week" ;;Saturday | Sunday ) echo "Free" ;;Friday ) echo "Hooray !!" ;;* ) echo "It is $DAY" ;;

esac

More the examples by yourself

(Cont)

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Iteration Statement

For statement

Iterate the value of the variable var through each word in the word listEvaluate the command in list after each iterationIf no word is supplied, $@ ($1 ..) is used insteadA break command causes the loop to terminateA continue command causes the loop to jump to the next iteration

for var {in [word]+}do

[result]done

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Examplefor color in red yellow green blue

do echo one color is $colordone

More the examples by yourself

(Cont)

Iteration Statement

for xdo echo x = $x

done

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Iteration Statement

While statement

while [condition]do

[result]done

test $var1 –opt $var2

(Cont)

test $var1 –opt $var2

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Examplewhile true do

who | grep u51xxxsleep 30

done

(Cont)

Iteration Statement

x=1while test $x -le 10do

echo x is $xx=`expr $x + 1`

done

More the examples by yourself

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

See More

[1] http://www.grymoire.com/Unix/Sh.html[2] http://www.ooblick.com/text/sh/[3] http://www.injunea.demon.co.uk/pages/page204.htm

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Chulalongkorn University

2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

End

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