Bash shell script to find if a number is perfect or not

In this article, we will discuss how to write a bash script to find if a number is perfect or not. A perfect number is defined as, a positive number that is equal to the sum of its proper divisors. Smallest no is 6 ex= 1,2,3 are divisor of 6 and 1+2+3=6

Method 1: Using While Loop

• Read the input using the read command.
• Then run while loop with condition i <= no/2 .
• Check if no%i is equals to 0 or not if true then add i to ans .
• After getting out of the while loop checks if the obtained value of variable sum is equal to no variable or not.
• If equals then return "$no is a perfect number " else "$no is not a perfect number " using echo command.

# !/bin/bash

echo "Enter a number"

# reading input from user 
read no  

# initializing the value of i
i=1

ans=0


# check if the value of left operand is less 
# than or equal to the value of right operand
# if yes, then the condition becomes true
while [ $i -le $((no / 2)) ]   

do
        # Checks if the value of two operands are
        # equal or not; if yes, then the condition
        # becomes true
        if [[ $((no%i)) -eq 0  ]] 
        then

                ans=$((ans + i))

fi

i = $((i + 1))

done

# Checks if the value of two operands are equal 
# or not; if yes, then the condition becomes true
if [ $no -eq $ans ]  
then
        # printing output
        echo "$no is perfect" 
        else
        
        # printing output
        echo "$no is NOT perfect" 
fi

Output:

1) perfect number 

2) not a perfect number

Method 2: Using For Loop

• Read the input using the read command.
• Then use for loop and iterate until no(input).
• Check if no%i is equaled to 0 or not if true then add i to ans .
• After getting out of for loop check if the obtained value of the variable sum is equal to no variable or not .
• If equals then return "$no is a perfect number " else "$no is not a perfect number " using echo command.

# !/bin/bash
echo "Enter a number"
read no  
i=1
ans=0
for i in 1 2 3 4 5 .. no  
do
        if [[ $((no%i)) -eq 0  ]]  
        then
            ans=$((ans + i))
            
fi
i=`expr $i + 1`
done

if [ $no -eq $ans ]  
then
        echo "$no is perfect"
        else
        echo "$no is NOT perfect"
fi

Output: 

1) perfect number

2) not perfect number

Time complexity: O(n) as using a loop

Auxiliary space: O(1)