Performing Arithmetic Operations in Bash: Multiplication

Bash scripting is a powerful skill for anyone working in the Linux environment, allowing you to automate tasks and streamline workflows. One fundamental aspect of scripting is performing arithmetic operations. In this guide, we'll focus on how to perform multiplication in Bash.

Understanding Bash Arithmetic

Bash, or the Bourne Again SHell, supports basic arithmetic operations like addition, subtraction, division, and multiplication. Arithmetic in Bash is typically performed using the double parentheses syntax (( ... )) or the expr command. While both are valid, the double parentheses syntax is more modern and offers more readability and functionality.

Syntax for Multiplication in Bash

Here's the straightforward way to perform multiplication in Bash using the double parentheses syntax:

1#!/bin/bash
2
3# Define variables
4num1=5
5num2=10
6
7# Perform multiplication
8result=$((num1 * num2))
9
10# Output the result
11echo "The result of multiplying $num1 and $num2 is: $result"
12

In this example, num1 and num2 are the numbers you want to multiply, and result stores the product.

Multiplying Variables

In Bash scripting, you can multiply variables without hassle. Here’s an example that shows how to multiply user-provided values:

1#!/bin/bash
2
3# Prompt user input
4echo "Enter first number:"
5read num1
6
7echo "Enter second number:"
8read num2
9
10# Multiplication
11result=$((num1 * num2))
12
13echo "The product of $num1 and $num2 is $result"
14

This script asks the user to input two numbers and then multiplies them.

Using expr for Multiplication

expr is another way to perform multiplication, especially useful in older scripts:

1#!/bin/bash
2
3# Using expr for multiplication
4num1=8
5num2=6
6result=$(expr $num1 \* $num2)
7
8echo "Using expr: The result of multiplying $num1 and $num2 is: $result"
9

In expr, the asterisk * needs to be escaped with a backslash \ to avoid shell interpretation.

Handling Floating Point Numbers

Bash natively does not support floating-point arithmetic. However, you can leverage external tools like bc or awk. Here’s an example using bc:

1#!/bin/bash
2
3num1=5.5
4num2=7.2
5result=$(echo "$num1 * $num2" | bc)
6
7echo "The result of $num1 multiplied by $num2 is $result"
8

Practical Applications

Calculating Disk Usage

A practical example is calculating disk space used by a certain number of files. Suppose each file is 4 MB, and you have 150 files:

1#!/bin/bash
2
3file_size=4  # in MB
4file_count=150
5total_size=$((file_size * file_count))
6
7echo "Total size for $file_count files is $total_size MB"
8

Conclusion

Understanding how to perform arithmetic operations, especially multiplication, can significantly enhance your Bash scripting skills. These operations are pivotal in various scripting scenarios, from simple calculations to complex automation tasks. For more on advancing your Bash script knowledge, you may want to check this detailed Bash scripting tutorial.

By mastering these basic scripts, you can start to automate more tedious tasks and optimize your productivity on the command line. Keep exploring, and consider following up with guides on Bash loops and conditionals.