Bash Script to Check Palindrome String Easily

Use a Bash script that reverses the input string with rev and compares it to the original using if [ "$str" = "$rev" ] to check if it's a palindrome.

Examples

Inputmadam

Outputmadam is a palindrome

Inputhello

Outputhello is not a palindrome

Inputa

Outputa is a palindrome

How to Think About It

To check if a string is a palindrome, think of reading it forwards and backwards. If both are the same, the string is a palindrome. So, reverse the string and compare it to the original.

Algorithm

1

Get the input string from the user

2

Reverse the input string

3

Compare the original string with the reversed string

4

If they are the same, print it is a palindrome

5

Otherwise, print it is not a palindrome

Code

bash

#!/bin/bash
read -p "Enter a string: " str
rev=$(echo "$str" | rev)
if [ "$str" = "$rev" ]; then
  echo "$str is a palindrome"
else
  echo "$str is not a palindrome"
fi

Output

Enter a string: madam
madam is a palindrome

Dry Run

Let's trace the input 'madam' through the code

1

Input string

User enters 'madam'

2

Reverse string

Reverse of 'madam' is 'madam'

3

Compare strings

'madam' equals 'madam', so it is a palindrome

Original String	Reversed String	Palindrome?
madam	madam	Yes

Why This Works

Step 1: Reversing the string

The rev command reverses the characters in the string, making it easy to compare.

Step 2: Comparing strings

Using [ "$str" = "$rev" ] checks if the original and reversed strings are exactly the same.

Step 3: Output result

If they match, the script prints the string is a palindrome; otherwise, it prints it is not.

Alternative Approaches

Using a loop to compare characters

bash

#!/bin/bash
read -p "Enter a string: " str
len=${#str}
palindrome=true
for (( i=0; i<len/2; i++ )); do
  if [ "${str:i:1}" != "${str:len-i-1:1}" ]; then
    palindrome=false
    break
  fi
done
if $palindrome; then
  echo "$str is a palindrome"
else
  echo "$str is not a palindrome"
fi

This method avoids external commands but is longer and more complex.

Using parameter expansion to reverse string

bash

#!/bin/bash
read -p "Enter a string: " str
rev=""
for (( i=${#str}-1; i>=0; i-- )); do
  rev+=${str:i:1}
done
if [ "$str" = "$rev" ]; then
  echo "$str is a palindrome"
else
  echo "$str is not a palindrome"
fi

Pure Bash approach without external commands but less efficient.

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

Time Complexity

The script reverses the string once, which takes O(n) time where n is the string length.

Space Complexity

It stores the reversed string, so space used is O(n).

Which Approach is Fastest?

Using rev is fastest and simplest; loop methods are slower and more complex.

Approach	Time	Space	Best For
Using rev command	O(n)	O(n)	Simple and fast palindrome check
Loop character comparison	O(n)	O(1)	No external commands, more control
Parameter expansion reverse	O(n)	O(n)	Pure Bash, no external tools