Bash Script to Print Right Triangle Pattern

Use a nested loop in Bash: for i in {1..n}; do for j in $(seq 1 $i); do echo -n "*"; done; echo; done prints a right triangle of stars with height n.

Examples

Inputn=1

Output*

Inputn=4

Output* ** *** ****

Inputn=0

Output

How to Think About It

To print a right triangle pattern, think of printing one star on the first line, two stars on the second, and so on until the nth line. Use one loop to count lines and a nested loop to print stars equal to the current line number.

Algorithm

1

Get the number of lines n from the user or set it.

2

For each line number i from 1 to n:

3

Print i stars on that line without a newline after each star.

4

After printing stars for the line, print a newline to move to the next line.

Code

bash

#!/bin/bash
n=5
for ((i=1; i<=n; i++))
do
  for ((j=1; j<=i; j++))
  do
    echo -n "*"
  done
  echo
 done

Output

*
**
***
****
*****

Dry Run

Let's trace n=3 through the code

1

Start outer loop i=1

Print 1 star: *

2

Next outer loop i=2

Print 2 stars: **

3

Next outer loop i=3

Print 3 stars: ***

i	Stars Printed
1	*
2	**
3	***

Why This Works

Step 1: Outer loop controls lines

The outer loop runs from 1 to n, each iteration representing one line of the triangle.

Step 2: Inner loop prints stars

The inner loop runs from 1 to the current line number i, printing stars without newlines.

Step 3: Newline after each line

After printing stars for a line, echo prints a newline to start the next line.

Alternative Approaches

Using seq and while loops

bash

#!/bin/bash
n=5
i=1
while [ $i -le $n ]
do
  j=1
  while [ $j -le $i ]
  do
    echo -n "*"
    ((j++))
  done
  echo
  ((i++))
done

Uses while loops instead of for loops; slightly longer but same logic.

Using printf with string repetition

bash

#!/bin/bash
n=5
for ((i=1; i<=n; i++))
do
  printf '%*s\n' "$i" '' | tr ' ' '*'
done

Uses printf and tr to print stars, avoiding inner loop; more concise but less intuitive.

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

Time Complexity

The outer loop runs n times and the inner loop runs up to n times, resulting in O(n^2) time.

Space Complexity

Only a few variables are used, so space complexity is O(1).

Which Approach is Fastest?

Using printf with string repetition can be faster and shorter, but nested loops are clearer for beginners.

Approach	Time	Space	Best For
Nested for loops	O(n^2)	O(1)	Clarity and beginners
While loops	O(n^2)	O(1)	Alternative loop style
printf with tr	O(n^2)	O(1)	Conciseness and speed