Bash Script to Print Pyramid Pattern with Loop

Use nested loops in Bash: for ((i=1; i<=n; i++)); do for ((j=n-i; j>0; j--)); do echo -n " "; done; for ((k=1; k<=2*i-1; k++)); do echo -n "*"; done; echo; done to print a pyramid pattern of height n.

Examples

Input3

Output * *** *****

Input5

Output * *** ***** ******* *********

Input1

Output*

How to Think About It

To print a pyramid, think of each line having spaces first, then stars. The number of spaces decreases each line, and the stars increase in an odd number pattern. Use one loop for lines, one for spaces, and one for stars.

Algorithm

1

Get the number of rows (height) from the user.

2

For each line from 1 to height:

3

Print spaces equal to height minus current line number.

4

Print stars equal to (2 times current line number) minus 1.

5

Move to the next line.

Code

bash

#!/bin/bash
read -p "Enter pyramid height: " n
for ((i=1; i<=n; i++))
do
  for ((j=n-i; j>0; j--))
  do
    echo -n " "
  done
  for ((k=1; k<=2*i-1; k++))
  do
    echo -n "*"
  done
  echo
 done

Output

Enter pyramid height: 5
    *
   ***
  *****
 *******
*********

Dry Run

Let's trace input 3 through the code

1

Line 1 (i=1)

Print 2 spaces (3-1=2), then 1 star (2*1-1=1)

2

Line 2 (i=2)

Print 1 space (3-2=1), then 3 stars (2*2-1=3)

3

Line 3 (i=3)

Print 0 spaces (3-3=0), then 5 stars (2*3-1=5)

Line (i)	Spaces (n-i)	Stars (2*i-1)
1	2	1
2	1	3
3	0	5

Why This Works

Step 1: Spaces create pyramid shape

Printing spaces before stars shifts the stars to the right, forming the pyramid shape. The count decreases each line with n - i.

Step 2: Stars form the pyramid body

Stars increase by odd numbers each line using 2*i - 1, making the pyramid wider as it goes down.

Step 3: Nested loops control layout

The outer loop controls lines, inner loops print spaces and stars in order, then a newline moves to the next line.

Alternative Approaches

Using printf for formatting

bash

#!/bin/bash
read -p "Enter pyramid height: " n
for ((i=1; i<=n; i++))
do
  printf "%*s" $((n - i)) ""
  printf "%0.s*" $(seq 1 $((2*i - 1)))
  echo
 done

This uses printf for cleaner spacing and star printing, which can be more efficient and readable.

Using while loops

bash

#!/bin/bash
read -p "Enter pyramid height: " n
i=1
while [ $i -le $n ]
do
  j=$((n - i))
  while [ $j -gt 0 ]
  do
    echo -n " "
    j=$((j - 1))
  done
  k=$((2 * i - 1))
  while [ $k -gt 0 ]
  do
    echo -n "*"
    k=$((k - 1))
  done
  echo
  i=$((i + 1))
done

This uses while loops instead of for loops, which some beginners find easier to understand.

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

Time Complexity

The script uses nested loops: the outer loop runs n times, and inner loops run up to n times, resulting in O(n^2) time.

Space Complexity

Only a few variables are used; no extra data structures, so space complexity is O(1).

Which Approach is Fastest?

Using printf can be slightly faster and cleaner than multiple echo calls, but both have the same time complexity.

Approach	Time	Space	Best For
For loops with echo	O(n^2)	O(1)	Simple and clear for beginners
Printf formatting	O(n^2)	O(1)	Cleaner output, slightly faster
While loops	O(n^2)	O(1)	Alternative loop style, easier for some