Bash Script to Print Odd Numbers from 1 to n

Use a Bash for loop with a step of 2 starting at 1: for ((i=1; i<=n; i+=2)); do echo $i; done to print odd numbers from 1 to n.

Examples

Input1

Output1

Input7

Output1 3 5 7

Input0

Output

How to Think About It

To print odd numbers from 1 to n, start counting from 1 and increase by 2 each time. This way, you only hit odd numbers. Stop when you reach or pass n.

Algorithm

1

Get the input number n.

2

Start a counter at 1.

3

While the counter is less than or equal to n, do:

4

Print the counter.

5

Increase the counter by 2.

6

Stop when the counter is greater than n.

Code

bash

#!/bin/bash
read -p "Enter a number n: " n
for ((i=1; i<=n; i+=2)); do
  echo $i
done

Output

Enter a number n: 7
1
3
5
7

Dry Run

Let's trace input n=7 through the code

1

Initialize i

i=1, n=7

2

Check condition i <= n

1 <= 7 is true, print 1

3

Increment i by 2

i=3

4

Repeat check and print

3 <= 7 true, print 3; i=5

5

Repeat check and print

5 <= 7 true, print 5; i=7

6

Repeat check and print

7 <= 7 true, print 7; i=9

7

Check condition fails

9 <= 7 false, stop

i
1
3
5
7

Why This Works

Step 1: Start at 1

We begin counting from 1 because it is the first odd number.

Step 2: Increment by 2

Adding 2 each time skips even numbers, so only odd numbers are printed.

Step 3: Stop at n

The loop stops when the number exceeds n to avoid printing numbers beyond the limit.

Alternative Approaches

Using modulo check inside a loop

bash

#!/bin/bash
read -p "Enter a number n: " n
for ((i=1; i<=n; i++)); do
  if (( i % 2 == 1 )); then
    echo $i
  fi
done

This checks every number but prints only odd ones; less efficient but easy to understand.

Using seq command with step

bash

read -p "Enter a number n: " n
seq 1 2 $n

Uses built-in seq command to generate odd numbers; very concise but depends on seq availability.

Complexity: O(n/2) time, O(1) space

Time Complexity

The loop runs roughly n/2 times because it increments by 2, so time complexity is O(n/2), which simplifies to O(n).

Space Complexity

The script uses constant extra space for variables, so space complexity is O(1).

Which Approach is Fastest?

The direct increment by 2 approach is fastest because it skips even numbers, unlike the modulo check method which tests every number.

Approach	Time	Space	Best For
Increment by 2 loop	O(n)	O(1)	Efficient and simple
Modulo check loop	O(n)	O(1)	Easy to understand, less efficient
seq command	O(n)	O(1)	Concise, depends on external command