SysProg-Tutor 03 Unix Shell Script Programming

Tutor Session - 3

Chulalongkorn
Tutor Session III:

UNIX Shell Script
University

Programming

Wongyos Keardsri (P’Bank)
Department of Computer Engineering
Faculty of Engineering, Chulalongkorn University
Bangkok, Thailand
Mobile Phone: 089-5993490
E-mail: wongyos@gmail.com, MSN: bankberrer@hotmail.com
Twitter: @wongyos
2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Tutor Outline
Chulalongkorn
University

Introduction to Shell Data Operations
Shell Decision Statements
Shell Script If-else
Variables Switch-case
Creating/Assigning Iteration Statement
Accessing For
Setting While
Getting Start Shell Script
Include shell
Create shell
Run shell

2 2110313 Operating Systems and System Programs (1/2010)

Tutor Session - 3

Introduction to Shell
Chulalongkorn
University

What is the shell or Unix shell?
A command-line interpreter and script host that
provides a traditional user interface for the Unix
operating system and for Unix-like systems
There are many shells; sh, bash, ksh, csh, zsh, …
Bourne Shell (sh)
Written by Stephen Bourne
Was the 1st popular Unix shell


Tutor Session - 3

Introduction to Shell
Chulalongkorn
University (Cont)
Bourne Shell (sh) (Cont)
Available on all Unix systems
Supports a fairly versatile programming language
A subset of more powerful Korn shell (ksh)
Implement with regular C programming
Executable file is stored as /bin/sh


Tutor Session - 3

Variables
Chulalongkorn
University

Creating and assigning a variable
name=value
No spaces
Printing/Showing a variable value
echo $name
With spaces
Setting environment variable
export NAME

Read only variable
readonly name

Tutor Session - 3

Variables
Chulalongkorn
University

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

More an examples by yourself


Tutor Session - 3

Variables
Chulalongkorn
University (Cont)
Accessing a variable
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.


Tutor Session - 3

Variables
Chulalongkorn
University (Cont)
Example
$ verb=sing
$ echo I like $verbing
I like
$ echo I like ${verb}ing
I like singing



Tutor Session - 3

Chulalongkorn
University

What is the shell script?
Similar to DOS batch files
Quick and simple programming
Text file interpreted by shell, effectively new command
List of shell commands to be run sequentially
Typical operations for file manipulation, program
execution, and printing text


Tutor Session - 3

Chulalongkorn
University (Cont)
Include full path to interpreter (shell)
#!/path/shell

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


Tutor Session - 3

Chulalongkorn
University (Cont)
Using vi command to create shell script file
Running shell script by using the command below
sh [file]

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


Tutor Session - 3

Chulalongkorn
University (Cont)
Interaction with user
Output value
echo [texts/variables]
Input value
read [variables]

Comment line
# your comments


Tutor Session - 3

Chulalongkorn
University (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


Tutor Session - 3

Chulalongkorn
University (Cont)
Example
$ cat example1.sh
echo there are $# command line arguments: $@
$ sh example1.sh
there are 0 command line arguments:
$ sh example1.sh x y z
there are 3 command line arguments: x y z



Tutor Session - 3

Data Operation
Chulalongkorn
University

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

Using expr to excute operators
expr $va1 op $var2


Tutor Session - 3

Data Operation
Chulalongkorn
University (Cont)
Conditional Expressions
test [expression]
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


Tutor Session - 3

Data Operation
Chulalongkorn
University (Cont)
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 characters
str1 = str2 True if str1 is equal to str2
str1 != str2 True if str1 is not equal to str2
string True if string is not null
int1 -eq int2 True if int1 is equal to int2
int1 -ne int2 True if int1 is not equal to int2
int1 -gt int2 True if int1 is greater than int2


Tutor Session - 3

Data Operation
Chulalongkorn
University (Cont)
test forms (Cont)
int1 -ge int2 True if int1 is greater than or equal to int2
int1 -lt int2 True if int1 is less than int2
int1 -le int2 True if int1 is less than or equalt to int2
!expr True if expr is false
expr1 -a expr2 True if ezpr1 and expr2 are true
expr1 -o expr2 True if ezpr1 or expr2 are true


Tutor Session - 3

Decision Statement
Chulalongkorn
University

If-else statement
if [condition]
then [result]
elif [condition]
then [result]
else
[result]
fi


Tutor Session - 3

Decision Statement
Chulalongkorn
University (Cont)
Example
if test -r file1
then echo "file1"
elif [ -r file2 ] test –r file2
then cp file2 file3
echo "file2 copy to file3"
else
echo "no file"
fi

More the examples by yourself


Tutor Session - 3

Decision Statement
Chulalongkorn
University (Cont)
Switch-case statement
case $var in
value1) [result] ;;
value2) [result] ;;
...
*) [result] ;;
Default case
esac


Tutor Session - 3

Decision Statement
Chulalongkorn
University (Cont)
Example
case $day in
Monday ) echo "A new week" ;;
Saturday | Sunday ) echo "Free" ;;
Friday ) echo "Hooray !!" ;;
* ) echo "It is $DAY" ;;
esac



Tutor Session - 3

Iteration Statement
Chulalongkorn
University

For statement
for var {in [word]+}
do
[result]
done
Iterate the value of the variable var through each word in the word
list
Evaluate the command in list after each iteration
If no word is supplied, $@ ($1 ..) is used instead
A break command causes the loop to terminate
A continue command causes the loop to jump to the next iteration

Tutor Session - 3

Iteration Statement
Chulalongkorn
University (Cont)
Example
for color in red yellow green blue
do echo one color is $color
done

for x
do echo x = $x
done



Tutor Session - 3

Iteration Statement
Chulalongkorn
University (Cont)
While statement
while [condition]
do test $var1 –opt $var2
[result]
done


Tutor Session - 3

Iteration Statement
Chulalongkorn
University (Cont)
Example
while true
do
who | grep u51xxx
sleep 30
done
x=1
while test $x -le 10
do
echo x is $x
x=`expr $x + 1`
done

Tutor Session - 3

See More
Chulalongkorn
University

[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


Tutor Session - 3

End
Chulalongkorn
University

Question ?

… Answer

SysProg-Tutor 03 Unix Shell Script Programming

Recommended

More Related Content

Viewers also liked (20)

Similar to SysProg-Tutor 03 Unix Shell Script Programming (11)

More from Wongyos Keardsri (20)

Recently uploaded (20)

SysProg-Tutor 03 Unix Shell Script Programming