Bash Math Operations (Bash Arithmetic) Explained

Bash math operations or Bash arithmetic refers to mathematical operations that can be performed within a Bash script. Bash is a command-line shell used in many Unix-based systems, including Linux and macOS. Bash arithmetic is a powerful feature of shell, allowing you to perform various math operations like addition, subtraction, multiplication, and division with ease.

In this article, we will explore basics of Bash arithmetic, including its syntax and various operations that can be performed with examples.

Basic Syntax of Bash Arithmetic

To perform Bash arithmetic, you need to use a special syntax that is different from regular arithmetic operators. basic syntax of Bash arithmetic is as follows −

$(( expression ))

The expression is mathematical operation you want to perform, and it can include variables, numbers, and operators. double parentheses are used to indicate that this is a Bash arithmetic operation.

Let's take a look at some examples to understand this syntax better.

Example 1: Addition

To add two numbers using Bash arithmetic, you can use following syntax −

$(( num1 + num2 ))

Here, num1 and num2 are two numbers you want to add. Let's say we want to add 5 and 10. Bash arithmetic expression for this will be −

$(( 5 + 10 ))

The output of this expression will be 15.

Example 2: Subtraction

To subtract two numbers using Bash arithmetic, you can use following syntax −

$(( num1 - num2 ))

Here, num1 and num2 are two numbers you want to subtract. Let's say we want to subtract 10 from 20. Bash arithmetic expression for this will be −

$(( 20 - 10 ))

The output of this expression will be 10.

Example 3: Multiplication

To multiply two numbers using Bash arithmetic, you can use following syntax −

$(( num1 * num2 ))

Here, num1 and num2 are two numbers you want to multiply. Let's say we want to multiply 3 and 4. Bash arithmetic expression for this will be −

$(( 3 * 4 ))

The output of this expression will be 12.

Example 4: Division

To divide two numbers using Bash arithmetic, you can use following syntax −

$(( num1 / num2 ))

Here, num1 and num2 are two numbers you want to divide. Let's say we want to divide 20 by 5. Bash arithmetic expression for this will be −

$(( 20 / 5 ))

The output of this expression will be 4.

Bash Arithmetic Operators

In Bash arithmetic, you can use various operators to perform mathematical operations. Here are some of operators that you can use −

Addition (+)

The addition operator is used to add two numbers. Here's an example −

Example

$(( 5 + 10 ))

Output

15

Subtraction (-)

The subtraction operator is used to subtract two numbers. Here's an example −

Example

$(( 20 - 10 ))

Output

10

Multiplication (*)

The multiplication operator is used to multiply two numbers. Here's an example −

Example

$(( 3 * 4 ))

Output

12

Division (/)

The division operator is used to divide two numbers. Here's an example −

Example

$(( 20 / 5 ))

Output

4

Note − When dividing two numbers, Bash will perform integer division by default. To perform floating-point division, you need to use bc command.

Modulo (%)

The modulo operator is used to get remainder of a division operation. Here's an example −

Example

$(( 10 % 3 ))

Output

1

In this example, we are using modulo operator to find remainder when 10 is divided by 3. output of this expression will be 1, as remainder is 1.

Exponentiation (**)

The exponentiation operator is used to raise a number to a power. Here's an example −

Example

$(( 2 ** 3 ))

Output

8

In this example, we are using exponentiation operator to raise 2 to power of 3, which is 8.

Increment (++)

The increment operator is used to increase value of a variable by 1. Here's an example −

Example

num=5
$(( num++ ))

Output

6

In this example, we are using increment operator to increase value of num variable by 1. output of this expression will be 6.

Decrement (--)

The decrement operator is used to decrease value of a variable by 1. Here's an example −

Example

num=5
$(( num-- ))

Output

4

In this example, we are using decrement operator to decrease value of num variable by 1. output of this expression will be 4.

Variables in Bash Arithmetic

In Bash arithmetic, you can also use variables to perform mathematical operations. Here's an example −

Example

num1=5
num2=10
$(( num1 + num2 ))

Output

15

In this example, we are using two variables num1 and num2 to perform addition operation. output of this expression will be 15.

You can also use variables and operators together to perform more complex mathematical operations. Here's an example −

Example

num1=5
num2=10
$(( (num1 + num2) * 3 ))

Output

45

In this example, we are using variables num1 and num2 to perform addition operation and then multiplying result by 3. output of this expression will be 45.

Using bc Command for Floating-Point Division

As mentioned earlier, when dividing two numbers in Bash arithmetic, result will be an integer by default. If you need to perform floating-point division, you can use bc command. bc command is a command-line calculator that can perform various mathematical operations, including floating-point division. Here's an example −

Example

$ echo "20/3" | bc -l

Output

6.66666666666666666666

In this example, we are using echo command to send expression "20/3" to bc command. -l option is used to load math library, which allows bc command to perform floating-point division. output of this expression will be 6.66666666666666666666, which is result of dividing 20 by 3.

Using Bash Arithmetic in Conditional Statements

Bash arithmetic can also be used in conditional statements, such as if statements and loops. Here's an example −

Example

num=5
if (($num > 0)); then
echo "The number is positive."
fi

Output

number is positive.

In this example, we are using if statement to check if value of num variable is greater than 0. (($num > 0)) syntax is used to perform comparison operation. If condition is true, message "The number is positive." will be printed.

Similarly, you can use Bash arithmetic in loops to perform various mathematical operations. Here's an example −

Example

for ((i=1; i<=10; i++)); do
echo $((i * 2))
done

Output

2
4
6
8
10
12
14
16
18
20

In this example, we are using a for loop to print first 10 even numbers. $((i * 2)) syntax is used to perform multiplication operation.

Conclusion

Bash arithmetic is a powerful feature of Bash shell that allows you to perform various mathematical operations with ease. In this article, we covered basics of Bash arithmetic, including its syntax and various operators. We also looked at how to use variables in Bash arithmetic to perform more complex mathematical operations.

With Bash arithmetic, you can perform various calculations and automate your scripts with ease. By understanding basics of Bash arithmetic, you can take advantage of this powerful feature to improve your scripting skills and increase your productivity.