Lab 7
Shell Script
Reference:
Linux Shell Scripting Tutorial v1.05r3
A Beginner's handbook
http://www.freeos.com/guides/lsst/index.html
Entering VI
 To call the VI editor and begin an editing session
$ vi file-name
 File-name does not exist  anew file will be created
 File-name exists  edit the existing file
Organization of VI
There are two modes of operation in VI:
 Command mode: where you tell the editor what
you want it to do.
 Text input mode: the part of the editor where
you inter material (text, data, or program code) .
press a or
i
Input mode
Operation Mode
press ESC
a : insert after the current position(cursor position).
i : insert before the current position(cursor position).
Command mode
Command mode
Input mode
You can do the following:
Enter(type or write):
-Change current position(move the cursor). - text, data, code.
-Delete.
-Show file name.
-Save and quit.
-Undo & Redo.
-Run shell command.
To change the current position(move the cursor):
in the command mode use the arrow in the keyboard
↑↓ → ←
Vi Text Editor keys:
Delete
x
X
 dw
 dd
 d0
 D$

) self study )
delete current character
delete previous character(backspace)
delete word forward
delete complete line
delete from cursor to beginning of line
delete to the end of the line
Vi Text Editor keys:
Ctrl+g
Show file name
Save and quit
ZZ or :wq
Save and quit
:w
Save only
:q
Quit (nothing added to save)
used when there are NO unsaved changes.
If you need to save, vi warns you:
E37: no write since last change(add ! To override)
:q!
Quit and don’t save
Then
press
ENTER
Vi Text Editor keys:
Undo and Redo
 u
Undo
 Ctrl+r
Redo
Run shell command
:!command
For example:
:!id
:!ls
:!ps
Shell script


What is Shell Script
“Shell Script is series of command written in plain
text file. “
Why to Write Shell Script?

Shell script can take input from user, file and output them on
screen.
 Useful to create our own commands.
 Save lots of time.
 To automate some task of day today life.
 System Administration part can be also automated.
Getting started with Shell
Programming

How to write shell script
Use any editor like vi or mcedit to write shell script.
2) After writing shell script set execute permission for
your script
syntax:
chmod permission your-script-name
1)
chmod 755 test
Getting started with Shell
Programming (cont.)
3)
Execute your script as
syntax:
bash your-script-name
sh your-script-name
./your-script-name
$ bash test
$ sh test
$ ./ test
Getting started with Shell
Programming (cont.)
$ vi first
#
# My first shell script
#
clear
echo "Knowledge is Power"
After saving the above script, you can run the script as follows:
$ chmod 755 first
$ ./first
Getting started with Shell
Programming (cont.)
$ vi first
Start vi editor
#
# My first shell script
#
# followed by any text is considered as
comment. Comment gives more information
about script, logical explanation about shell
script.
Syntax:
# comment-text
clear
clear the screen
echo "Knowledge is Power"
To print message or value of variables on
screen, we use echo command, general form
of echo command is as follows
syntax:
echo "Message"
Before type
ENTER.
After type
ENTER.
Frist press any of
“a , o , i “
to
allow to type that
text and commands
inside test file.
Press “ Esc “ to convert
from input mode to
Command mode.
Then press
“Ctr l+ :”
And type wq to save this
change in file.
Enter…

Variables
in
Shell
In Linux, there are two types of variable:
(1) System variables - Created and maintained by Linux itself. This type of variable defined
in CAPITAL LETTERS.
(2) User defined variables (UDV) - Created and maintained by user. This type of variable
defined in lower letters.

How to define and print User Defined Variables:
Syntax to define UDV
variable name = value
Syntax to print or access value of UDV
$variablename
Example:
- To define variable called 'vech' having value Bus and print contains of variable
'vech'
vech=Bus
echo $vech
- To define variable called n having value 10 and print contains of variable ‘n'
n=10
echo $n
Rules for Naming variable name
1)
begin with Alphanumeric character or underscore character (_), followed by one
or more Alphanumeric character
HOME
vech
2)
Don't put spaces on either side of the equal sign
no=10
no =10 wrong
no= 10 wrong
no = 10 wrong
3)
Variables are case-sensitive, just like filename in Linux.
no=10
No=11
4)
You can define NULL variable as follows:
vech=
vech=""
5)
Do not use ?,* etc, to name your variable names.
Shell Arithmetic
Syntax:
expr op1 math-operator op2
expr 1 + 3
expr 2 - 1
expr 10 / 2
expr 20 % 3
expr 10 \* 3
echo 6 + 3  will print 6+3
echo `expr 6 + 3`  will print 9
expr 6+3  will not work because no space between number and operator
• define two variable x=20, y=5 and then to print division of x and y
x=20
y=5
expr $x / $y
• store division of x and y to variable called z
x=20
y=5
z=`expr $x / $y`
echo $z
The Read Statement
Use to get input (data from user) from keyboard and store
(data) to variable
Syntax:
read variable1 variable2 variableN
Example1:
$ vi sayH
#
#Script to read your name from key-board
#
echo "Your first name please:“
read fname
echo "Hello $fname, Lets be friend!
Run it as follows:
$ chmod 755 sayH
$ ./sayH
"
Example2:
$ vi summation
#
#Script to read two numbers from key-board and calculate
their sum
#
echo “Enter two numbers:“
read x y
echo “The sum $x and $y is `expr $x + $y`”
Run it as follows:
$ chmod 755 summation
$ ./summation