Find Largest of Three Numbers in Bash

In this tutorial, you will learn how to find the largest of three numbers in a Bash script using nested if statements or a combination of if, elif, and else, along with comparison operators.

Using If-Elif-Else Statement to Find the Largest of Three Numbers

We can use the if statement along with elif and else to compare three numbers. The logic involves checking the relationship between the numbers step by step:

  1. If the first number is greater than or equal to the second and third numbers, it is the largest.
  2. If the second number is greater than or equal to third number, it is the largest.
  3. Otherwise, the third number is the largest.

The comparison is done using the -ge operator, which stands for “greater than or equal to”.

Here’s an example of how to implement this logic in Bash:

largest_of_three.sh

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#!/bin/bash
# Define three numbers
num1=10
num2=20
num3=15

# Compare the three numbers to find the largest
if [ $num1 -ge $num2 ] && [ $num1 -ge $num3 ]; then
  echo "$num1 is the largest number."
elif [ $num2 -ge $num3 ]; then
  echo "$num2 is the largest number."
else
  echo "$num3 is the largest number."
fi

Explanation:

  1. Define three numbers: Three variables, num1, num2, and num3, are initialized with the values 10, 20, and 15, respectively.
  2. Check the conditions:
    • The first if condition checks if num1 is greater than or equal to both num2 and num3. If true, num1 is the largest.
    • The elif condition checks if num2 is greater than or equal to num3. If true, num2 is the largest.
    • If both conditions are false, the else block executes, indicating that num3 is the largest.
  3. Output the largest number: The echo command is used to print the largest number to the console.
  4. End of script: The script ends after determining and displaying the largest number.

Output

20 is the largest number.

To make the script more dynamic, let’s modify it to accept user input for the three numbers. This allows the user to enter any three numbers and determine the largest.

largest_of_three.sh

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#!/bin/bash
# Prompt the user to enter three numbers
echo "Enter the first number:"
read num1
echo "Enter the second number:"
read num2
echo "Enter the third number:"
read num3

# Compare the three numbers to find the largest
if [ $num1 -ge $num2 ] && [ $num1 -ge $num3 ]; then
  echo "$num1 is the largest number."
elif [ $num2 -ge $num1 ] && [ $num2 -ge $num3 ]; then
  echo "$num2 is the largest number."
else
  echo "$num3 is the largest number."
fi

Explanation:

  1. Prompt the user for input:
    • The script prompts the user to enter the first number and reads it into num1.
    • The user is then prompted to enter the second and third numbers, which are read into num2 and num3, respectively.
  2. The rest of the steps are the same as in the previous script.

Example Output:

Enter the first number:
25
Enter the second number:
10
Enter the third number:
15
25 is the largest number.