Shell Script Programming

Explanation

1. Purpose

This Bash script asks the user to enter three numbers, compares them using conditional logic, and displays the largest number among them.

2. Key Concepts

• User Input (read -p): Prompts the user and stores their response in a variable.
• Conditional Logic (if / elif / else): Executes different code blocks based on specific conditions.
• Integer Comparison Operator (-ge): Checks if a number is "greater than or equal to" another.
• Logical Operator (&&): Represents the "AND" operation, requiring both conditions to be true.

3. Code Walkthrough

1. Getting Input:

   read -p "Enter the first number: " num1
   

   Prompts the user three separate times and saves the numbers into variables: num1, num2, and num3.

2. First Check (if):

   if [ "$num1" -ge "$num2" ] && [ "$num1" -ge "$num3" ]; then
   

   Checks if num1 is greater than or equal to both num2 and num3. If so, it prints num1.

3. Second Check (elif):

   elif [ "$num2" -ge "$num1" ] && [ "$num2" -ge "$num3" ]; then
   

   If num1 isn't the largest, it checks if num2 is greater than or equal to both num1 and num3. If so, it prints num2.

4. Default Case (else):

   else
       echo "The largest number is: $num3"
   

   If neither num1 nor num2 is the largest, then num3 must be the largest by default, so it prints num3.

4. Output

The program outputs a text prompt for each number, followed by the final result.

Example Terminal Session:

Enter the first number: 12
Enter the second number: 45
Enter the third number: 7
The largest number is: 45