Shell Programming
Introduction:
The shell is
the unix system mechanism for interfacing between user and the system.It is
command interpreter that reads line typed by the user and causes the execution
of the requested system features. Three of the most popular shells are Bourne
shell,berkely$shell and kern shell. The Bourne shell has been the primary at
Unix system shell.Shell command language includes control flow capabilities
command language program may be written using if…then..else,case..while for
structure. These programs are written in interfacing editors like vi editors.
Shell
programming is a series of unix command executed one by one.
1) The #Symbol:
This
symbol is used in shell script to reverse the value that is scanned.
2) The $Symbol:
This
command is used in shell script to reverse the value that is scanned.
3) The read Command:
This
command is used in shell script to reverse the value of the variable.
Syntax:
read
Variable name
4) The echo command:
This
command is used to display what ever message we want to display on the screen.
Arithmetic Operation &
Expression:
The arithmetic operators
provided by the shell are Addition in operator, Subtraction in operators,
Multiplication & Division/operator. The “expr” command helps us in getting
the numerical value of the digit strings.
Logical Operators:
a - Used
for indicating “AND ”
o - Used
for indicating “OR”
Comparison
Operators:
n1-eq
n2 will check if the integer are
equal
n1-ne
n2 will check if the two integer
are not equal
n1-gt
n2 will check if the integer n1
is greater than n2
n1-lt
n2 will check if the integer n1
is less than n2
n1-ge
n2 will check if the integer n1
is greater than or equal to n2
n1-le
n2 will check if the integer n1
is less than or equal to n2
Programming Language Constructs:
The if construct:
Syntax 1
If(condition)
then
command
else
command
fi
The case Construct:
Syntax:
case
value n
Choice
1) commands;;
Choice
2) command;;
Esac
The for command:
Syntax:
for<variable>in
value1,value2……….
do
command
done
The while Construct:
Syntax:
while
control command
do
command
list
done
The until loop:
Syntax:
until
control command
do
command
done
The execution Commands:
A
shell script can be executed in two ways
1)
Type in “sb FILENAME” at the $ prompt.
2)
Grant execute permission to the file and then type in the FILENAME at the $prompt
The Debug Command:
This
command is used for debugging the program.
Syntax:
sb-
x filename.
ARITHMETIC
OPERATION USING SHELL PROGRAM
To write a shell Program to do the
Arithmetic Operations like Addition, Subtraction, Multiplication, Division.
ALGORITHM:
Step
1: Start
Step
2: Read
the values of ‘a’ and ‘b’
Step
3: Write
the expression to calculate sum, difference, Product, Quotient and Remainder.
Step
4: Print
the Results
Step
5: Stop.
SHELL PROGRAM:
echo
"Enter Two Numbers"
read a b
c=`expr
$a + $b`
d=`expr
$a - $b`
e=`expr
$a \* $b`
f=`expr
$a / $b`
g=`expr
$a % $b`
echo
"Sum = $c"
echo
"Difference = $d"
echo
"Product = $e"
echo
"Quotient = $f"
echo
"Remainder = $g"
SAMPLE OUTPUT:
Enter
Two Numbers
12 10
Sum = 22
Difference
= 2
Product
= 120
Quotient
= 1
Remainder
= 2
RESULT: Thus
the shell Program to do arithmetic operation was executed without any errors.
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