Bash Script to Reverse a String with Example

You can reverse a string in Bash using rev command like echo "yourstring" | rev or using parameter expansion with a loop to reverse manually.

Examples

Inputhello

Outputolleh

InputBash123

Output321hsaB

Input

Output

How to Think About It

To reverse a string in Bash, think of reading the string from the end to the start and building a new string by adding characters one by one in reverse order. Alternatively, use the built-in rev command that does this efficiently.

Algorithm

1

Get the input string.

2

Initialize an empty string to hold the reversed result.

3

Loop through the input string from the last character to the first.

4

Add each character to the reversed string.

5

Output the reversed string.

Code

bash

#!/bin/bash
read -p "Enter a string: " str
reversed=""
len=${#str}
for (( i=len-1; i>=0; i-- )); do
  reversed+=${str:i:1}
done
echo "$reversed"

Output

Enter a string: hello
olleh

Dry Run

Let's trace reversing the string 'abc' through the code

1

Input string

str = 'abc'

2

Initialize reversed

reversed = ''

3

Loop i=2 (last char)

reversed = 'c'

4

Loop i=1

reversed = 'cb'

5

Loop i=0

reversed = 'cba'

6

Output

cba

Iteration	Index i	Character	Reversed string
1	2	c	c
2	1	b	cb
3	0	a	cba

Why This Works

Step 1: Reading input

The script reads the string from the user using read.

Step 2: Looping backwards

It uses a for loop starting from the last character index to zero to access characters in reverse order.

Step 3: Building reversed string

Each character is appended to the reversed variable, creating the reversed string step by step.

Alternative Approaches

Using rev command

bash

#!/bin/bash
read -p "Enter a string: " str
echo "$str" | rev

This is the simplest and fastest method but requires the <code>rev</code> utility to be installed.

Using awk

bash

#!/bin/bash
read -p "Enter a string: " str
echo "$str" | awk '{for(i=length;i!=0;i--)x=x substr($0,i,1);}END{print x}'

Uses awk to reverse string, useful if <code>rev</code> is not available but less readable.

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

Time Complexity

The script loops through each character once, so time grows linearly with string length.

Space Complexity

It creates a new string to hold the reversed result, so space also grows linearly.

Which Approach is Fastest?

Using the rev command is fastest and simplest, while manual loops are more flexible but slower.

Approach	Time	Space	Best For
Manual loop	O(n)	O(n)	Learning and no external tools
rev command	O(n)	O(n)	Quick and efficient string reversal
awk method	O(n)	O(n)	When rev is unavailable