Linux Shell Programming

Steps to Create a Linux Program

Step 1 – Open Linux in command mode and make a new directory at the Linux prompt (say $) to store newly created Linux program file either online or offline, and change the directory only one time.

Step 2 – Now create a new, fresh Linux file (say, for eg- Fibonacci.sh, here .sh is the extension of a Linux shell file) using Unix/Linux ‘vi’ Editor to write and save the Linux program in it.

$ vi  Fabonacci.sh (Press Enter)

Step 3 – Now Press I/i button to enter insert mode and start typing the program codes inside Fabonacci.sh file in the vi Linux editor.

Step 4 – Complete the Linux program in the Fibonacci.sh file.

Step 5 – Now press the ‘Esc‘ button to come out of Insert mode after finishing the code of the program.

Step 6 – Now again press the colon (:) symbol to come out of the program area and press enter. Now: symbol appears at the bottom of the editor page.

Step 7 – Now type ‘wq‘ word to come out from the ‘vi’ Editor with saving the program.

Step 8 – Now, to run/execute/debug the saved program –

$ sh  Fabonacci.sh (Press Enter)          [Either Output or Error will appear – Press Enter/ ]

• • • When output will appear –  Press Enter to do the next job/work after seeing the result.
    • When Error will appear – Press  CTRL+D – Again, repeat steps 2-7 to edit the program, save it, and execute it again. The same process is repeated many times until the correct output comes.

$ vi  Fabonacci.sh (Press Enter) . . . and follow step2-8

Keys used during editing a Linux or Shell Program for the movement of the cursor in the VI Editor

(a) Cursor Movement Keys/Commands :

(b) Character Deletion Keys/Commands :

• Back Space(CTRL+H) : Deletes the character to the left of the cursor.
• CTRL+D : Deletes the character under the cursor (not to the left).
• Ctrl + W: Deletes the word to the left of the cursor.
• Ctrl + U: Deletes the entire line to the left of the cursor.
• Ctrl + K: Deletes the entire line to the right of the cursor.
• Ctrl + Y: Yank (paste) the last deleted text. Works after using commands like Ctrl + U or Ctrl + K.

Popular Online Link to Execute/Run Shell Program without Installation of Linux in the System

Link1  Link2  Link3  Link4  Link5  Link6  

Example : Write a shell script or Linux program to show messages differently using an echo statement.

At $ or Linux Command Prompt :
   
   $ echo Shell script is case sensitive (press enter)

   Output : Shell script is case sensitive

   --------------------------------------  OR --------------------------------------
   $ echo Welcome       U     All       in Codershelpline (press enter)

   Output : Welcome U All in Codershelpline   
   --------------------------------------  OR --------------------------------------
   $ echo "Welcome U All in Codershelpline" (press enter)

   Output : Welcome U All in Codershelpline   
   --------------------------------------  OR --------------------------------------
   $ echo "Welcome   U     All in        Codershelpline" (press enter)

   Output : Welcome   U     All in        Codershelpline
  --------------------------------------  OR --------------------------------------
   $ echo "Welcome   U     All in        Codershelpline"; (press enter)

   Output : Welcome   U     All in        Codershelpline
 --------------------------------------  OR --------------------------------------
   $ echo 'Welcome   U     All in        Codershelpline' (press enter)

   Output : Welcome   U     All in        Codershelpline
--------------------------------------  OR --------------------------------------
echo Welcome  
echo 2022 

Output : 
Welcome  
2022
--------------------------------------  OR --------------------------------------
echo -n Welcome 
echo 2022 

Output : 
Welcome2022 
--------------------------------------  OR --------------------------------------
echo -n Welcome 
echo -n "  " 
echo 2022 

Output : 
Welcome  2022 

NB : In linux by default each echo command print contents with a new line but to print the contents in same horozontal line we use -n.

--------------------------------------  OR --------------------------------------

At vi Editor as a Shell script File :

   (do the code Similar as $ prompt but without $ in a shell file)

   echo Welcome U in Codershelpline (press enter)

   Output : Welcome U in Codershelpline  [After execution of created shell script file] 

Example : Write a shell script program in Linux to assign static or user values to shell variables and display them.

  # value initialization in shell variable

  clear
  x=24
  y=57
  z=96

  echo $x $y $z
  24 57 96
--------------------------------------  OR --------------------------------------
  clear  
  x=24; y=57; z=96.352;

  echo $x $y $z
  24 57 96.352  
--------------------------------------  OR --------------------------------------
  clear
  x="IGNOU"; y=57; z="Robert3258";

  echo $x $y $z
  IGNOU 57 Robert3258
--------------------------------------  OR --------------------------------------
  clear
  echo Enter first value
  read x
  25

  echo $x
  25

  echo Enter second value
  read y
  55

  echo $y
  55
--------------------------------------  OR --------------------------------------
  clear
  echo Enter three values
  read x y z
  25 58 69

  echo $x $y $z
  25 58 69
--------------------------------------  OR --------------------------------------
  echo Enter values for variables
  read x1 x2 x3
  55 12 38 97 95 85

  echo $x1 $x2 $x3
  55 12 38 97 95 85

  echo $x1 
  55

  echo $x2 
  12

  echo $x3
  38 97 95 85

Example : Write a shell script or program in Linux to calculate constant or shell variable values and display them.

$ expr 1 + 2 (press enter)
3

$ expr 7 - 2 (press enter)
5

$ expr 7 '*' 2 (press enter)
14

$ expr 7 \* 2 (press enter)
14

$ expr 9 / 2 (press enter)
4

$ expr 7 % 2 (press enter)
1

Example: Write a shell script or Linux program to display the Current Date and Time.

echo "Current System/Server Date and Time is = $(date)"

Output:
Current System/Server Date and Time is = Fri Jan  3 16:57:29 UTC 2025

Example : Write a shell script or Linux program to take two user values, store them in two shell variables, and display their total.

(Program is writeen at vi Editor in a Shell File :)

  clear
  echo Enter first value
  read x

  echo Enter second value
  read y

  z=`expr $x + $y`  
  echo The addition result of $x + $y is = $z


NB : ` is Smart quotes,not single quotes, located above tab button is used with expr statements.

Example : Write a shell script or Linux program to take required input values from the users at run time to calculate and display simple interest values.

 clear
 echo Enter Principal value :
 read p

 echo Enter rate value :
 read r

 echo Enter time value :
 read t

 si=`expr '(' $p \* $r \* $t ')' / 100`
 echo Simple Interest is '=' $si

Example : Write a shell script or Linux program to display the accepted value as Larger, Smaller, or Equal using the if statement.

echo Enter first value
read a

echo Enter second value
read b

if [ $a == $b ]
then
    echo "Both value is same"
fi

if [ $a -gt $b ]
then
    echo "First value is Larger"
fi

if [ $a -lt $b ]
then
    echo "Second value is Larger"
fi

Example : Write a shell script or Linux program to check whether the accepted value is Odd or Even using an If-else Statement.

clear
echo -n "Enter a number:"
read x

if [ `expr $x % 2` == 0 ]
then
	echo "$x is Even no."
else
	echo "$x is Odd no."
fi

-------------  OR  -------------

echo "Enter a number:"
read num

if [ $((num % 2)) -eq 0 ]
then
    echo "Entered Number $num is Even"
else
    echo "Entered Number $num is Odd"
fi

-------------  OR  -------------

read -p "Enter a number: " num
if ((num % 2 == 0)); then
    echo "$num is even."
else
    echo "$num is odd."
fi

Output:
Enter a number: 10
10 is even.

-------------  OR  -------------

read -p "Enter a number: " num
if ((num % 2 == 0)) 
then
    echo "$num is even."
else
    echo "$num is odd."
fi

Output:
Enter a number: 15
15 is odd.

-------------  OR  -------------

# SHELL SCRIPT TO CHECK CHARACTER IS VOWEL OR CONSONANT

echo "Enter a character:"
read ch

if [[ $ch == "a" || $ch == "e" || $ch == "i" || $ch == "o" || $ch == "u" ]]
then
    echo "The Input character is Vowel"
else
    echo "The Input character is Consonant"
fi

-------------  OR  -------------

# SHELL SCRIPT TO CHECK PALINDROME STRING

read -p "Enter a string value : " str
rev1=$(echo $str | rev)
if [[ $str == $rev1 ]]
then
    echo "$str is a palindrome."
else
    echo "$str is not a palindrome."
fi

Output:
Enter a string value : madam
madam is a palindrome.

------------  OR  -------------

# SHELL SCRIPT TO CHECK THE INPUT VALUE IS DIVISIBLE BY 5 AND 11

echo "Enter a number:"
read num

if [ $((num % 5)) -eq 0 ] && [ $((num % 11)) -eq 0 ]
then
    echo "The $num is Divisible by 5 and 11"
else
    echo "The $num is Not Divisible by 5 and 11"
fi

------------  OR  -------------

echo "Enter Username:"
read uname

echo "Enter Password:"
read pass

if [ "$uname" = "admin" ] && [ "$pass" = "1234" ]
then
    echo "Login Successful"
else
    echo "Invalid Username or Password"
fi

Example : Write a shell script or Linux program to display the names of the days of the week when we enter numeric values from 1-7 using the if-elif-else statement.

clear
 echo Enter your choice from 1-7
 read x

if [ $x == 1 ]
then
   echo "Sunday"
elif [ $x == 2 ]
then
   echo "Monday"
elif [ $x == 3 ]
then
   echo "Tuesday"
elif [ $x == 4 ]
then
   echo "Wednesday"
elif [ $x == 5 ]
then
   echo "Thursday"
elif [ $x == 6 ]
then
   echo "Friday"
elif [ $x == 7 ]
then
   echo "Saturday"
else
   echo "Invalid Choice"
fi

-------------  OR  -------------

# SHELL SCRIPT TO CHECK NUMBER IS NEGATIVE OR POSITIVE

echo "Enter a number:"
read num

if [ $num -gt 0 ]
then
    echo "Given Number is Positive"
elif [ $num -lt 0 ]
then
    echo "Given Number is Negative"
else
    echo "Given Number is Zero"
fi

-------------  OR  -------------

# SHELL SCRIPT TO CHECK NUMBER IS LARGER

echo "Enter first number:"
read a

echo "Enter second number:"
read b

if [ $a -gt $b ]
then
    echo "$a is greater than $b"
elif [ $b -gt $a ]
then
    echo "$b is greater than $a"
else
    echo "$a is equal to $b"
fi

Example : Write a shell script or Linux program to print the Largest value from three values.

read -p "Enter three numbers : " a b c
if ((a > b && a > c))
then
    echo "$a is the largest value."
elif ((b > a && b > c))
then
    echo "$b is the largest value."
else
    echo "$c is the largest value."
fi

Output:
Enter three numbers : 20 11 31
31 is the largest value.

-------------  OR  -------------

# SHELL SCRIPT TO CHECK NUMBER IS LARGER

echo "Enter three numbers:"
read a b c

if [ $a -gt $b ] && [ $a -gt $c ]
then
    echo "$a is greatest"
elif [ $b -gt $c ]
then
    echo "$b is greatest"
else
    echo "$c is greatest"
fi

Example : Write a shell script or Linux program to print all the values from 1 to 10 present in the list using a for loop.

for x in 1 2 3 4 5 6 7 8 9 10
do
    echo $x
done

Output:
1
2
3
4
5
6
7
8
9
10

--------------------  OR  --------------------

for i in {1..10}
do
    echo $i
done

--------------------  OR  --------------------

for i in {1..10..3}
do
    echo $i
done
--------------------  OR  --------------------

for i in {10..1..3}
do
    echo $i
done

OUTPUT:
10
7
4
1
--------------------  OR  --------------------

for ((i=10; i>=1; i--))
do
    echo $i
done

--------------------  OR  --------------------

for i in {A..Z}
do
    echo -n "$i "
done

Output:
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
 
--------------------  OR  --------------------

for i in {a..z}
do
    echo -n "$i "
done
Output:
a b c d e f g h i j k l m n o p q r s t u v w x y z 

--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 1 TO 10 HORIZONTALLY

clear
for x in 1 2 3 4 5 6 7 8 9 10
do
    echo -n "$x "
done

Output: 1 2 3 4 5 6 7 8 9 10
 
--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 11 TO 20 HORIZONTALLY IN OTHER WAY

clear
for num in {11..20}
do
  echo -n "$num "
done

Output: 11 12 13 14 15 16 17 18 19 20

--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 10 TO 22 HORIZONTALLY IN OTHER WAY

clear
for ((i=10;i<=22;i++))
do
  echo -n "$i "
done

Output:10 11 12 13 14 15 16 17 18 19 20 21 22

--------------------  OR  --------------------

# DISPLAY THE EVEN NUMBER FROM 2 TO 20 VERTICALLY

for ((i=2; i<=20; i=i+2))
do
    echo $i
done

--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 10 TO 22 HORIZONTALLY IN OTHER WAY

clear
for num in $(seq 10 22)
do
  echo -n "$num "
done

Output:10 11 12 13 14 15 16 17 18 19 20 21 22

--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 10 TO 30 HORIZONTALLY WITH THE INTERVAL OF +4

clear
for num in $(seq 10 4 30)
do
  echo -n "$num "
done

Output:
10 14 18 22 26 30 

--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 30 TO 10 HORIZONTALLY WITH THE INTERVAL OF -3

clear
for num in $(seq 30 -3 10)
do
  echo -n "$num "
done

Output: 30 27 24 21 18 15 12 

--------------------  OR  --------------------

# DISPLAY THE NUMBER FROM 50 TO 40 HORIZONTALLY WITH THE INTERVAL OF -1

clear
for num in $(seq 50 -1 40)
do
  echo -n "$num "
done

Output: 50 49 48 47 46 45 44 43 42 41 40

--------------------  OR  --------------------

# LINUX SHELL SCRIPT FOR SUM OF 1 TO 10 VALUES

sum=0

for ((i=1; i<=10; i++))
do
    sum=$((sum+i))
done

echo "Sum Total is = $sum"

--------------------  OR  --------------------

# LINUX SHELL SCRIPT FOR PRINTING TABLE

echo "Enter number:"
read num

for ((i=1; i<=10; i++))
do
    echo "$num x $i = $((num*i))"
done

--------------------  OR  --------------------

# LINUX SHELL SCRIPT FOR FACTORIAL RESULT

read -p "Enter a number for factorial : " num
fact=1
for ((i=1; i<=num; i++))
do
    fact=$((fact * i))
done
echo "Factorial of $num is $fact."

Output:
Enter a number for factorial : 5
Factorial of 5 is 120.

--------------------  OR  --------------------

# LINUX SHELL SCRIPT TO PRINT 7 or 10 FIBONACCI SERIES VALUES
 
read -p "Enter number of terms for Fibonacci series : " val
a=0
b=1
echo "Fibonacci series are :"
echo -n "$a "
echo -n "$b "
for ((i=0; i<val-2; i++))
do
    fn=$((a + b))
    echo -n "$fn "
    a=$b
    b=$fn
done
echo   # for cursor in next line after output

Output:
Enter number of terms for Fibonacci series : 7
Fibonacci series are :
0 1 1 2 3 5 8 

--------------------  OR  --------------------

a=0
b=1
echo "Fibonacci Series Values are : "

for ((i=1; i<=10; i++))
do
    echo $a
    c=$((a+b))
    a=$b
    b=$c
done

--------------------  OR  --------------------

# LINUX SHELL SCRIPT FOR REVERSE THE NUMBER

echo "Enter number:"
read num
rev=0

while [ $num -gt 0 ]
do
    rem=$((num%10))
    rev=$((rev*10+rem))
    num=$((num/10))
done

echo "Reverse value is = $rev"

--------------------  OR  --------------------

# LINUX SHELL SCRIPT TO COUNT THE DIGITS IN A NUMBER

echo "Enter number:"
read num

count=0

while [ $num -gt 0 ]
do
    num=$((num/10))
    count=$((count+1))
done

echo "Digits = $count"

-------------------  OR  --------------------

# LINUX SHELL SCRIPT TO SUM OF EACH DIGIT OF A NUMBER

echo "Enter number:"
read num

sum=0

while [ $num -gt 0 ]
do
    rem=$((num%10))
    sum=$((sum+rem))
    num=$((num/10))
done

echo "Sum of digits = $sum"

-------------------  OR  --------------------

# LINUX SHELL SCRIPT FOR THE NUMBER IS PRIME OR NOT

echo "Enter number:"
read num

count=0

for ((i=1; i<=num; i++))
do
    if [ $((num%i)) -eq 0 ]
    then
        count=$((count+1))
    fi
done

if [ $count -eq 2 ]
then
    echo "Prime Number"
else
    echo "Not Prime"
fi

--------------------  OR  --------------------

# LINUX SHELL SCRIPT TO CHECK THE NUMBER IS PALINDROME OR NOT

echo "Enter number:"
read num

temp=$num
rev=0

while [ $num -gt 0 ]
do
    rem=$((num%10))
    rev=$((rev*10+rem))
    num=$((num/10))
done

if [ $temp -eq $rev ]
then
    echo "Palindrome"
else
    echo "Not Palindrome"
fi

--------------------  OR  --------------------

# LINUX SHELL SCRIPT TO CHECK THE NUMBER IS ARMSTRONG OR NOT

echo "Enter number:"
read num

temp=$num
sum=0

while [ $num -gt 0 ]
do
    rem=$((num%10))
    sum=$((sum + rem*rem*rem))
    num=$((num/10))
done

if [ $temp -eq $sum ]
then
    echo "Armstrong Number"
else
    echo "Not Armstrong"
fi

--------------------  OR  --------------------

# DISPLAY THE NUMBER GIVEN FROM USERS AT RUN TIME HORIZONTALLY

clear
echo "Enter two values :"
read m
read n
echo "The output are :"
for num in $(seq "$m" "$n")
do
  echo -n "$num "
done

Output:
Enter two values :
10
20
The output are :

10 11 12 13 14 15 16 17 18 19 20

--------------------  OR  --------------------

# DISPLAY THE NUMBER VERTICALLY USING BREAK STATEMENT 

for x in 1 2 3 4 5 6 7 8 9 10
do    
    if [ $x == 8 ]
    then
        break
    fi    
    echo $x
done

Output:
1
2
3
4
5
6
7

--------------------  OR  --------------------

# DISPLAY THE NUMBER VERTICALLY USING CONTINUE STATEMENT
 
for x in 1 2 3 4 5 6 7 8 9 10
do    
    if [ $x == 5 ]
    then
        continue
    fi    
    echo $x
done

Output:
1
2
3
4
6
7
8
9
10

# DISPLAY THE PATTERN USING NESTED LOOP STATEMENT

for ((i=1; i<=5; i++))
do
    for ((j=1; j<=5; j++))
    do
        echo -n "* "
    done
    echo
done

Output:
* * * * * 
* * * * * 
* * * * * 
* * * * * 
* * * * *

--------------------  OR  --------------------

for ((i=1; i<=5; i++))
do
    for ((j=1; j<=i; j++))
    do
        echo -n "* "
    done
    echo
done

Output:
*
* *
* * *
* * * *
* * * * *

--------------------  OR  --------------------

for ((i=5; i>=1; i--))
do
    for ((j=1; j<=i; j++))
    do
        echo -n "* "
    done
    echo
done

Output:
* * * * * 
* * * * 
* * * 
* * 
* 

--------------------  OR  --------------------

for ((i=1; i<=5; i++))
do
    for ((j=1; j<=i; j++))
    do
        echo -n "$j "
    done
    echo
done

Output:
1 
1 2 
1 2 3 
1 2 3 4 
1 2 3 4 5

--------------------  OR  --------------------

for ((i=1; i<=5; i++))
do
    for ((j=1; j<=i; j++))
    do
        echo -n "$i "
    done
    echo
done
Output:
1 
2 2 
3 3 3 
4 4 4 4 
5 5 5 5 5

--------------------  OR  --------------------

num=1
for ((i=1; i<=5; i++))
do
    for ((j=1; j<=i; j++))
    do
        echo -n "$num "
        num=$((num+1))
    done
    echo
done

Output:(Floyd’s Triangle Shape)
1 
2 3 
4 5 6 
7 8 9 10 
11 12 13 14 15

--------------------  OR  --------------------

for i in A B C D E
do
    for j in A B C D E
    do
        echo -n "$j "
        
        if [ "$j" = "$i" ]
        then
            break
        fi
    done
    echo
done

Output:
A 
A B 
A B C 
A B C D 
A B C D E

--------------------  OR  --------------------

rows=5

for ((i=1; i<=rows; i++))
do
    for ((j=i; j<rows; j++))
    do
        echo -n " "
    done

    for ((k=1; k<=((2*i-1)); k++))
    do
        echo -n "*"
    done

    echo
done

Output:
    *
   ***
  *****
 *******
*********

--------------------  OR  --------------------

rows=5

for ((i=rows; i>=1; i--))
do
    for ((j=rows; j>i; j--))
    do
        echo -n " "
    done

    for ((k=1; k<=((2*i-1)); k++))
    do
        echo -n "*"
    done

    echo
done

Output:
*********
 *******
  *****
   ***
    *

Example : Write a shell script or Linux program that prints all the values from 1 to 10 using a while loop.

# Shell script to print no. from 1-10
clear
x=1
 while [ $x -lt 11 ]
do    
    echo $x  
    
    x=`expr $x + 1`
done

Output:
1
2
3
4
5
6
7
8
9
10

Example : Write a shell script or Linux program to print all the values from 1-10 using the Until loop.

clear
x=1
 
#This loop continues until the value of x becomes greater than 10
until [ $x -gt 10 ]
do    
    echo $x    
    x=`expr $x + 1`
done

NB:
- The until loop is executed as many as times, the condition/command evaluates to false.
- This loop terminates when the condition/command becomes true.

Example : Write a shell script or Linux program to create and print the contents differently using the Case-Esac statement.

 echo "Enter two numbers:"
read a b

echo "Choose 1 for Addition, 2 for Subtraction 3 for Multiply and 4 for Divide"
read choice

case $choice in
1) echo "Sum is = $((a+b))" ;;
2) echo "Difference is = $((a-b))" ;;
3) echo "Product is = $((a*b))" ;;
4) echo "Division is = $((a/b))" ;;
*) echo "Invalid Choice"
esac

--------------------  OR  --------------------

 clear
 echo Enter your numeric choice from 1-7
 read x

case $x in
    
    1) echo "Sunday" ;;
   
    2) echo "Monday" ;;
    
    3) echo "Tuesday" ;;
    
    4) echo "Wednesday" ;;
    
    5) echo "Thursday" ;;
    
    6) echo "Saturday" ;;
    
    *) echo "Invalid choice" ;;
esac

--------------------  OR  --------------------

clear
 echo Enter your letter choice as a/s/m/d
 read x

case $x in
    
    "a") echo "Addition" ;;
    "A") echo "Addition" ;;
   
    "s") echo "Subtraction" ;;
    
    "m") echo "Multiplication" ;;
    
    "d") echo "Division" ;;
    
    *) echo "Invalid choice" ;;
esac

--------------------  OR  --------------------

clear
 echo Enter your letter choice as add/sub/mul/div
 read x

case $x in
    
    "add") echo "Addition" ;;
    "Add") echo "Addition" ;;
   
    "sub") echo "Subtraction" ;;
    "Sub") echo "Subtraction" ;;
    
    "mul") echo "Multiplication" ;;
    "Mul") echo "Multiplication" ;;
    
    "div") echo "Division" ;;
    "Div") echo "Division" ;;
    
    *) echo "Invalid choice" ;;
esac

Output:
Enter your letter choice as add/sub/mul/div
ADD
Invalid choice

--------------------  OR  --------------------

clear
 echo Enter your letter choice as add/sub/mul/div
 read x

case $x in
    
    "add"|"Add") echo "Addition" ;;
   
    "sub"|"Sub") echo "Subtraction" ;;
    
    "mul"|"Mul") echo "Multiplication" ;;
    
    "div"|"Div") echo "Division" ;;
    
    *) echo "Invalid choice" ;;
esac

Output:
Enter your letter choice as add/sub/mul/div
Sub
Subtraction

--------------------  OR  --------------------

# LINUX SHELL SCRIPT OF SIMPLE CALCULATOR

echo "Enter two numbers:"
read num1 num2
echo "Choose operation: +, -, *, /"
read opr
case $opr in
    +) echo "Addition Result is : $((num1 + num2))";;
    -) echo "Subtractio Result is : $((num1 - num2))";;
    \*) echo "Multiplication Result is : $((num1 * num2))";;
    /) echo "Division Result is : $((num1 / num2))";;
    *) echo "Invalid Choice, Change it";;
esac

Output:
Enter two numbers:
10 5
Choose operation: +, -, *, /
/
Division Result is : 2

--------------------  OR  --------------------

clear
 echo Enter your numeric choice from 1-12
 read x

case $x in
    
    1|3|5|7|8|10|12)echo "Month is of 31 days" ;;
    
    2) echo "Month is of 28/29 days" ;;
    
    4|6|9|11)echo "Month is of 30 days" ;;
    
    *) echo "Invalid choice" ;;
esac

--------------------  OR  --------------------

echo "Choose any one option from the menu below :"

select choice in "Display Current Date" "List Existing Files" "Check Uptime" "Exit"
do
  case $choice in
    "Display Current Date")
      echo "The current date and time is:"
      date
      ;;
    "List Existing Files")
      echo "The files in the current directory are:"
      ls
      ;;
    "Check Uptime")
      echo "System uptime is:"
      uptime
      ;;
    "Exit")
      echo "Exiting the script. Goodbye!"
      break
      ;;
    *)
      echo "Invalid option. Please select a valid choice."
      ;;
  esac
done

Output:
Choose any one option from the menu below :
1) Display Current Date	 3) Check Uptime
2) List Existing Files	 4) Exit
#? 1
The current date and time is:
Thu Dec 12 16:25:20 UTC 2024
#? 4
Exiting the script. Goodbye!

--------------------  OR  --------------------

while true
do
    echo "Choose anyOne option"
    echo "1.Date"
    echo "2.Calendar"
    echo "3.Exit"

    read choice

    case $choice in
        1) date ;;
        2) cal ;;
        3) exit ;;
        *) echo "Invalid Choice"
    esac
done

Example : Write a shell script or Linux program to create and print the Array values in different ways.

# SHELL SCRIPT TO DECLARE, STORE AND DISPLAY ELEMENT FROM OF AN ARRAY

# Declare an array with name X and display all elements

X=(10 20 30 40 50)
echo "All elements in Array X: ${X[@]}"

Output : All elements in Array X: 10 20 30 40 50

------------  OR -------------

# SHELL SCRIPT TO ADD A NEW ELEMENT IN AN ARRAY

# Declare an array with name X and display all elements
X=(10 20 30 40 50)
echo "All elements in Array X: ${X[@]}" 
# Add new values to the array X
X[5]=60
echo "Array elements after adding value : ${X[@]}" 

Output :All elements in Array X: 10 20 30 40 50
Array elements after adding value : 10 20 30 40 50 60

------------  OR -------------

# SHELL SCRIPT TO DISPLAY SPECIFIC ELEMENT FROM OF AN ARRAY

# Declare an array with name X 
X=(10 20 30 40 50)
# Access and display a specific value at location 3
echo "Element at index 2: ${X[2]}" 

Output : Element at index 2: 30

------------  OR -------------

# SHELL SCRIPT TO DISPLAY ALL ARRAY ELEMENTS USING LOOP

X=(10 20 30 40 50)

# Display array elements through Loop 
for val in "${X[@]}"
do
  echo -n "$val "
done

Output: 10 20 30 40 50

------------  OR -------------

# SHELL SCRIPT TO DELETE/REMOVE A SPECIFIC ARRAY ELEMENT

# Declare an array with name X
X=(10 20 30 40 50)
echo "Array elements before Deletion : ${X[@]}" 

# Remove specific value from the array X
unset X[2]

echo "Array elements after specific Deletion : ${X[@]}"

Array elements before Deletion : 10 20 30 40 50
Array elements after specific Deletion : 10 20 40 50

------------  OR -------------

# SHELL SCRIPT TO FIND LARGEST VALUE FROM ARRAY ELEMENTS

arr=(12 45 67 23 89)
largest=${arr[0]}

for i in "${arr[@]}"
do
    if [ $i -gt $largest ]
    then
        largest=$i
    fi
done

echo "Largest value is = $largest"

------------  OR -------------

# SHELL SCRIPT TO DELETE/REMOVE THE ALL ARRAY ELEMENTS

# Declare an array with name X
X=(10 20 30 40 50)
echo "Array elements before Deletion : ${X[@]}" 

# Remove all values from the array X
unset X

echo "Array elements after all Deletion : ${X[@]}"

Output : 
Array elements before Deletion : 10 20 30 40 50
Array elements after Deletion :

------------  OR -------------

# SHELL SCRIPT TO FIND OUT THE LENGTH/SIZE OF AN ARRAY

# Declare an array with name X
X=(10 20 30 40 50)
echo "Array elements are : ${X[@]}" 

# Get the number of elements/Length of Array X
echo "Array length = ${#X[@]}"

Array elements are : 10 20 30 40 50
Array length = 5

------------  OR ------------- 

# SHELL SCRIPT TO INPUT DYNAMIC VALUES DIFFERENTLY IN AN ARRAY

# Initialize an array of constant size 5
X=(5)

# Read/store 5 values into the array dynamically
echo "Enter 5 values:"
 #for i in $(seq 0 4)
for ((i=0; i<5; i++))
do
  read -p "Value $((i+1)): " value
  X[i]=$value # Append value to the array
done

# Display the 5 values from the array
echo "The entered  5 values are:"

#for val in "${X[@]}"
#do
  #echo "$val"
#done

echo "All the elements in Array X: ${X[@]}" 

Output:
Enter 5 values:
Value 1: 10
Value 2: 20
Value 3: 30
Value 4: 40
Value 5: 50
The entered  5 values are:
All the elements in Array X: 10 20 30 40 50

------------  OR ------------- 

# SHELL SCRIPT TO DISPLAY THE DYNAMIC VALUES DIFFERENTLY IN AN ARRAY

# Initialize an array of constant size 5
X=(5)

# Read/store 5 values into the array dynamically
echo "Enter 5 values:"
 #for i in $(seq 0 4)
for ((i=0; i<5; i++))
do
  read -p "Value $((i+1)): " value
  X[i]=$value # Append value to the array
done

# Display the 5 values from the array
echo "The entered  5 values are:"

for i in $(seq 0 4)
do
    echo -n "${X[$i]} "
done

#for ((i=0;i<=4;i++))
#do
  #echo -n "${X[$i]} "
#done

Output : 
Enter 5 values:
Value 1: 10
Value 2: 20
Value 3: 30
Value 4: 40
Value 5: 50
The entered  5 values are:
10 20 30 40 50 

------------  OR -------------

# SHELL SCRIPT TO STORE AND DISPLAY DYNAMIC VALUES

# Initialize an array of constant size 5
X=(5)

# Read/store 5 values into the array dynamically
echo "Enter 5 values:"
 #for i in $(seq 0 4)
for ((i=0; i<5; i++))
do
  read -p "Value $((i+1)): " value
  X[i]=$value # Append value to the array
done

# Display the 5 values from the array
echo "The entered 5 values are:"

len=${#X[@]}

for ((i=0;i<=$len-1;i++))
do
  echo -n "${X[$i]} "
done

Output : 
Enter 5 values:
Value 1: 1
Value 2: 2
Value 3: 3
Value 4: 4
Value 5: 5
The entered 5 values are:
1 2 3 4 5
 
------------  OR -------------

# SHELL SCRIPT TO REVERSE ARRAY ELEMENTS

X=(5)

# Read/store 5 values into the array dynamically
echo "Enter 5 values:"
 #for i in $(seq 0 4)
for ((i=0; i<5; i++))
do
  read -p "Value $((i+1)): " value
  X[i]=$value # Append value to the array
done

# Display the 5 values from the array
echo "The entered 5 values in reversed are:"
for ((i=9;i>=0;i--))
do
  echo -n "${X[$i]} "
done

Output:
Enter 5 values:
Value 1: 10
Value 2: 20
Value 3: 30
Value 4: 40
Value 5: 50
The entered 5 values in reversed are:
50 40 30 20 10 

------------  OR -------------

# SHELL SCRIPT TO COPY ONE ARRAY ELEMENTS INTO ANOTHER

X=(5)
Y=(5)

# Read/store 5 values into the array dynamically
echo "Enter 5 values in first array :"
 #for i in $(seq 0 4)
for ((i=0; i<5; i++))
do
  read -p "Value $((i+1)): " value
  X[i]=$value # Append value to the array
done

# Copy the Values into other array
for ((i=0;i<=9;i++))
do
  Y=("${X[@]}")
  #Y[$i]="${X[$i]}"
done

echo "The copied elements in other Array are : ${Y[@]}"

Output :
Enter 5 values in first array :
Value 1: 2
Value 2: 4
Value 3: 6
Value 4: 8
Value 5: 10
The copied elements in other Array are : 2 4 6 8 10
 
------------  OR -------------

# SHELL SCRIPT TO ACCEPT ARRAY SIZE & VALUES DYNAMICALLY

# Initialize an empty array
X=()

# Prompt(-p) the user for the number of values(n) to store
read -p "Give the value for array size? " n

# Read/store values into the array dynamically
echo "Enter $n values:"
for ((i=0; i<n; i++))
do
  read -p "Value $((i+1)): " value
  X[i]=$value # Append value to the array
done

# Display the values from the array
echo "The entered values are:"

#for val in "${X[@]}"
#do
  #echo "$val"
#done

echo "All the elements in Array X: ${X[@]}"

Output:
Give the value for array size? 5
Enter 5 values:
Value 1: 10
Value 2: 20
Value 3: 30
Value 4: 40
Value 5: 50
The entered values are:
All the elements in Array X: 10 20 30 40 50

------------  OR -------------

arr[0,0]="A"
arr[0,1]="B"
arr[0,2]="C"

arr[1,0]="D"
arr[1,1]="E"
arr[1,2]="F"

arr[2,0]="G"
arr[2,1]="H"
arr[2,2]="I"

for ((i=0; i<3; i++))
do
    for ((j=0; j<3; j++))
    do
        echo -n "${arr[$i,$j]} "
    done
    echo
done

Output:
A B C
D E F
G H I

------------  OR -------------

for ((i=0; i<3; i++))
do
    for ((j=0; j<3; j++))
    do
        echo "Enter value for arr[$i,$j]:"
        read arr[$i,$j]
    done
done

echo "Two-Dimensional Array Elements"

for ((i=0; i<3; i++))
do
    for ((j=0; j<3; j++))
    do
        echo -n "${arr[$i,$j]} "
    done
    echo
done

Output:
10 20 30
40 50 60
70 80 90

Example : Write a shell script or Linux program to print the String Values differently.

fruits="Apple Orange Mango Banana"

for x in $fruits
do
    echo $x
done

Output:
Apple
Orange
Mango
Banana

NB:
- The for loop operates/works on lists of items mainly. 
- The loop continues for every item present in the list. 

------------  OR -------------

# SHELL SCRIPT TO REVERSE THE STRING

read -p "Enter a string : " str
echo "Reversed string is : $(echo $str | rev)"

Output:
Enter a string : Welcome
Reversed string is : emocleW