Case statements used in Shell Script

Last Blog Review →

In the last blog we understood, why WHILE LOOP is used and it’s syntax along with some examples of using WHILE LOOP.

1. What are Case Statements →

The if condition block with a lot of if-else statement can be written in better way using "case statement".

2. Case statement syntax →

case <<value>> in
        1) .... ;;
        2) .... ;;
        *) .... ;;
esac

3. Shell Script example using case statements

a. Shell Script to print the month by giving number as inputs

i-002978a646c30dd8b (EC2)
-------------------------
-lp10:~$ vim print-month-name.sh 
-lp10:~$ cat print-month-name.sh    
month_number=$1

if [ -z $month_number ]
then
  echo "No month number given. Please enter a month number as a command line argument."
  echo "eg: ./print-month-number 5"
  exit
fi

if [[ $month_number -lt 1 && $month_number -gt 12 ]]
then
  echo "Invalid month number given. Please enter a valid number - 1 to 12."
  exit
fi

case $month_number in
  1) echo "January" ;;
  2) echo "February" ;;
  3) echo "March" ;;
  4) echo "April" ;;
  5) echo "May" ;;
  6) echo "June" ;;
  7) echo "July" ;;
  8) echo "August" ;;
  9) echo "September" ;;
  10) echo "October" ;;
  11) echo "November" ;;
  12) echo "December" ;;
esac
-lp10:~$ chmod 700 print-month-name.sh 
-lp10:~$ ./print-month-name.sh       
No month number given. Please enter a month number as a command line argument.
eg: ./print-month-number 5
-lp10:~$ ./print-month-name.sh 7
July
-lp10:~$

b. Shell script for implementing calculator using case statements

i-002978a646c30dd8b (EC2)
-------------------------
-lp10:~$ vim calculator.sh 
-lp10:~$ cat calculator.sh 
#!/bin/bash
while true
do
  echo "1. Average"
  echo "2. Subsctract"
  echo "3. Multiply"
  echo "4. Divide"
  echo "5. Quit"

  read -p "Enter your choice: " choice

case $choice in
   1)
      read -p "Enter Number1: " number1
      read -p "Enter Number2: " number2
      sum=$(( number1 + number2 ))
      echo Answer=$(echo "$sum / 2" | bc -l)
      ;;
   2)
      read -p "Enter Number1: " number1
      read -p "Enter Number2: " number2
      echo Answer=$(( $number1 - $number2 ))
      ;;

    3)
      read -p "Enter Number1: " number1
      read -p "Enter Number2: " number2
      echo Answer=$(( $number1 * $number2 ))
      ;;
    4)
      read -p "Enter Number1: " number1
      read -p "Enter Number2: " number2
      echo Answer=$(( $number1 / $number2 ))
      ;;
    5)
      break
      ;;
  esac
done
-lp10:~$ chmod 700 calculator.sh 
-lp10:~$ ./calculator.sh 
1. Average
2. Subsctract
3. Multiply
4. Divide
5. Quit
Enter your choice: 2
Enter Number1: 5
Enter Number2: 1
Answer=4

Conclusion

In the this blog we understood, the use of case statements to use instead of using multiple if else statements along with its syntax and shell scripts.