Bash Script to Check Even or Odd Number

Use the Bash script with the modulo operator like if (( number % 2 == 0 )); then echo \"Even\"; else echo \"Odd\"; fi to check if a number is even or odd.

Examples

Input4

Output4 is Even

Input7

Output7 is Odd

Input0

Output0 is Even

How to Think About It

To check if a number is even or odd, divide it by 2 and look at the remainder. If the remainder is 0, the number is even; otherwise, it is odd.

Algorithm

1

Get the input number from the user.

2

Calculate the remainder when the number is divided by 2.

3

If the remainder is 0, print that the number is even.

4

Otherwise, print that the number is odd.

Code

bash

#!/bin/bash
read -p "Enter a number: " number
if (( number % 2 == 0 )); then
  echo "$number is Even"
else
  echo "$number is Odd"
fi

Output

Enter a number: 5
5 is Odd

Dry Run

Let's trace input 5 through the code

1

Input number

User enters 5, so number=5

2

Calculate remainder

5 % 2 = 1 (not zero)

3

Check remainder

Since remainder is 1, print '5 is Odd'

Step	Operation	Value
1	Input number	5
2	5 % 2	1
3	Output	5 is Odd

Why This Works

Step 1: Using modulo operator

The % operator gives the remainder of division, which helps determine evenness.

Step 2: Condition check

If remainder is zero, the number divides evenly by 2, so it is even.

Step 3: Output result

Print a clear message stating if the number is even or odd.

Alternative Approaches

Using arithmetic expansion with if-else

bash

#!/bin/bash
read -p "Enter a number: " n
remainder=$(( n % 2 ))
if [ $remainder -eq 0 ]; then
  echo "$n is Even"
else
  echo "$n is Odd"
fi

This uses classic test brackets and arithmetic expansion, which is more portable but slightly longer.

Using case statement

bash

#!/bin/bash
read -p "Enter a number: " num
case $((num % 2)) in
  0) echo "$num is Even";;
  1) echo "$num is Odd";;
esac

Using case can be cleaner for multiple conditions but is less common for simple even/odd checks.

Complexity: O(1) time, O(1) space

Time Complexity

The modulo operation and condition check run in constant time regardless of input size.

Space Complexity

Only a few variables are used, so space usage is constant.

Which Approach is Fastest?

All approaches use simple arithmetic and condition checks, so they have similar performance; choice depends on readability and style.

Approach	Time	Space	Best For
Modulo with (( ))	O(1)	O(1)	Simple and modern Bash scripts
Modulo with [ ] test	O(1)	O(1)	More portable scripts
Case statement	O(1)	O(1)	When extending to multiple conditions