Bash Script -Part 2

Bash Script 2

ARITHMETIC OPERATORS

There are 11 arithmetic operators which are supported by Bash Shell.

Those are ,

1. Addition
2. Subtraction
3. Multiplication
4. Division
5. Exponentiation
6. Modulo
7. Increment and Decrement

Double parentheses is the easiest mechanism to perform basic arithmetic operations in the Bash shell.

Syntax

((expression))

#Method 1

Sum=$((10+3))
echo "Sum = $Sum"

#Method 2

((Sum=10+3))
echo "Sum = $Sum"

#Method 3

Num1=10
Num2=3
((Sum=Num1+Num2))
echo "Sum = $Sum"

#Method 4

Num1=10
Num2=3
Sum=$((Num1+Num2))
echo "Sum = $Sum"

CONTROL STATEMENT

Control Statements works based on the Condition

Control Statements are two type.Those are,

1. Conditional Statement
2. Looping Statement
3. Jumping Statement

IF Statement

Syntax :

if [ expression ];

then

statements

fi

#EXAMPLE For IF statement
read -p " Enter number : " number  
  
if [ $number -gt 125 ]  
then  
echo "Value is greater than 125"  
fi  

BASH IF ELSE

Syntax :

if [ condition ];

then

<if block commands>

else

<else block commands>

fi

#!/bin/bash  
  
#when the condition is true  
if [ 10 -gt 3 ];  
then  
  echo "10 is greater than 3."  
else  
  echo "10 is not greater than 3."  
fi  
  
#when the condition is false  
if [ 3 -gt 10 ];  
then  
  echo "3 is greater than 10."  
else  
  echo "3 is not greater than 10."  
fi

Bash Nested If Statement

#!/bin/bash
read -p "Enter a value:" value
if [ $value -gt 9 ];
then
if [ $value -lt 11 ];
then
echo "$value>9, $value<11"
else
echo "The value you typed is greater than 9."
fi
else echo "The value you typed is not greater than 9."
fi

BASH ELSE IF

Syntax :

if [ condition ];

then

<commands>

elif [ condition ];

then

<commands>

else

<commands>

fi

#!/bin/bash  
  
read -p "Enter a number of quantity:" num  
  
if [ $num -gt 100 ];  
then  
echo "Eligible for 10% discount"  
elif [ $num -lt 100 ];  
then  
echo "Eligible for 5% discount"  
else  
echo "Lucky Draw Winner"  
echo "Eligible to get the item for free"  
fi 

BASH CASE

Syntax :

case expression in

pattern_1)

statements

;;

pattern_2)

statements

;;

pattern_3|pattern_4|pattern_5)

statements

;;

pattern-n)

statements

;;

*)

statements

;;

esac

#!/bin/bash  
  
echo "Which Operating System are you using?"  
echo "Windows, Android, Chrome, Linux, Others?"  
read -p "Type your OS Name:" OS  
  
case $OS in  
    Windows|windows)  
        echo "That's common. You should try something new."  
        echo  
        ;;  
    Android|android)  
        echo "This is my favorite. It has lots of applications."  
        echo  
        ;;  
    Chrome|chrome)  
        echo "Cool!!! It's for pro users. Amazing Choice."  
        echo  
        ;;  
    Linux|linux)  
        echo "You might be serious about security!!"  
        echo  
        ;;  
    *)  
        echo "Sounds interesting. I will try that."  
        echo  
        ;;  
esac

LOOPING STATEMENTS

Loops used to perform repetitive tasks.There are three types are available.Those are,

1. For Loop
2. While Loop
3. Until -While Loop

FOR LOOP

Syntax -1

for variable in list

do

commands

done

Syntax -2

for (( expression1; expression2; expression3 ))

do

commands

done

    #!/bin/bash  
    #For Loop to Read Three-expression  
      
    for ((i=1; i<=10; i++))  
    do  
    echo "$i"  
    done  

WHILE LOOP

The bash while loop can be defined as a control flow statement which allows executing the given set of commands repeatedly as long as the applied condition evaluates to true.

Syntax

while [ expression ];

do

commands;

multiple commands;

done

    #!/bin/bash  
    #Script to get specified numbers  
      
    read -p "Enter starting number: " snum  
    read -p "Enter ending number: " enum  
      
    while [[ $snum -le $enum ]];  
    do  
    echo $snum  
    ((snum++))  
    done  
      
    echo "This is the sequence that you wanted."  

UNTIL LOOP

Bash Until Loop in a bash scripting is used to execute a set of commands repeatedly based on the boolean result of an expression

until [ expression ];

do

….

Statements

…..

done

#!/bin/bash  
    #Bash Until Loop example with multiple conditions  
      
    max=5  
    a=1  
    b=0  
      
    until [[ $a -gt $max || $b -gt $max ]];  
    do  
    echo "a = $a & b = $b."  
    ((a++))  
    ((b++))  
    done

JUMPING STATEMENT

Break -It Terminate the process of execution

#!/bin/bash  
#Table of 2  
  
for table in {2..100..2}  
do  
echo $table  
if [ $table == 20 ]; then  
break   #break statement terminate the execution
fi  
done

Continue -This keyword used to skip the execution

    #!/bin/bash  
    #Numbers from 1 to 20, ignoring from 6 to 15 using continue statement"  
      
    for ((i=1; i<=20; i++));  
    do  
    if [[ $i -gt 5 && $i -lt 16 ]];  
    then  
    continue  
    fi  
    echo $i  
    done  

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