Simple Calculator in Bash

Create a simple calculator which can perform basic arithmetic operations like addition, subtraction, multiplication or division depending upon the user input in Bash.

Example: 

Enter two numbers:
5.6
3.4
Enter Choice: 
1. Addition
2. Subtraction
3. Multiplication
4. Division
3
5.6 * 3.4 = 19.0 

Approach:

1. Read Two Numbers
2. Input Choice (1-Addition, 2-Subtraction, 3-Multiplication, 4-Division) 
3. if Choice equals 1
    Calculate res = a + b
   else If Choice equals 2
    Calculate res = a - b
   else if Choice equals 3
    Calculate res = a * b
   else if Choice equals 4
    Calculate res = a / b
4. Output Result, res

Commands/Statement Used:

1. echo
echo is one of the mostly used command. 
It is used to print a line of text in standard output.  

$ echo [-neE] [arg ...] 

2. read
The command read in Linux is used to read the input from the keyboard. 
3. Switch-Case
When there are a lot of if statement in Shell and it becomes confusing. Then it is good to use case statement.
4. bc Command
Checkout the link for bc Command bc Command Linux Example

Bash

# !/bin/bash

# Take user Input
echo "Enter Two numbers : "
read a
read b

# Input type of operation
echo "Enter Choice :"
echo "1. Addition"
echo "2. Subtraction"
echo "3. Multiplication"
echo "4. Division"
read ch

# Switch Case to perform
# calculator operations
case $ch in
  1)res=`echo $a + $b | bc`
  ;;
  2)res=`echo $a - $b | bc`
  ;;
  3)res=`echo $a \* $b | bc`
  ;;
  4)res=`echo "scale=2; $a / $b" | bc`
  ;;
esac
echo "Result : $res"

Output:

Time Complexity: O(1)
Auxiliary Space: O(1)

References:
Array Basics Shell Scripting | Set 2 (Using Loops)
Array Basics in Shell Scripting | Set 1
Sorting an array in Bash using Bubble sort
bc Command Linux Example