Using bc Command in Linux and Bash Scripts

The bc command in Linux is used for mathematical calculation. It’s more than just a command; it’s a language. But you are likely to use it as a command for floating point mathematical operations.

Yes. unlike other programming languages, bash does not have a float variable option.

Apart from the floating point operations, you can also use it in the terminal for arithmetic operations.

In this tutorial, I will cover both ways to use the bc command: in the bash script and in the terminal window.

How to use the bc command in Linux

Contents

1 How to use the bc command in Linux
2 More on bash

To use the bc command, you’d have to follow the given command syntax:

bc [options] [file]

Here,

[options] is used to change the default behavior of the bc command.
[file] is where you append the file to perform calculations from data within the file.

Both [options] and [file] are optional which means you can use the bc command without any of these.

To use the bc command in the terminal, all you have to do is execute the bc command and it will open a prompt where you can type arithmetic operations:

As you can see, it can easily calculate operations with decimals.

To exit, you can either type and execute quit or press Ctrl + D.

Now, let’s have a look at some examples.

1. Deal with decimals

As I mentioned in the beginning, the bc command is used when your output has decimals, but by default, it won’t show any.

Now, there are two ways to manage decimals:

Executing the bc command with the -l flag (easy)
Using the scale option (gives flexibility)

Let’s start with the first one.

Using the bc command with the -l

When you execute the bc command with the -l flag, it loads the math library which enables you to use all the advanced calculation functions.

And if you wish to do so, you can be done with the following:

bc -l

The only downside of using this method is it will show around 20 decimal placeholders every time you perform a division.

use bc command to manage decimal placeholders without scale option

Using the scale option

This is another method where you use scale and specify how many decimal placeholders you want.

For example, if I were to divide 9 by 2, then, the answer should be 4.5 so I have to have one decimal placeholder. So I will use scale=1:

how to deal with float values while using the bc command

As you can see, how the output differs with and without the scale option.

2. Calculate without the bc prompt

Alternatively, you can get a similar output without using the bc prompt.

To do so, you can write any arithmetic operation with the scale option to decide how many decimals there should be and pipe it to the bc command:

echo "scale=no_of_decimals; arithmatic_operation_here" | bc

For example, here, I want to divide 15 by two so I have to have one decimal, then, I will use scale=1 and pipe it to the bc command:

echo "scale=1; 15/2" | bc

calculate float values without bc prompt in Linux

3. Use variables with the bc command

The usage of variables with the bc command is quite straightforward. All you have to do is execute the bc command, assign some variables, and then perform arithmetic operations with variables.

First, execute the bc command:

bc

Then assign values to variables. Such as here, I assigned 2 to a and 3 to b:

a=2
b=3

After that, you can perform any arithmetic operation you want to. For example, here, I did the addition:

a+b

4. Use the math library with the bc command

Using the math library, you can find out the value of trigonometry functions, logarithms, and a lot more.

First, start the bc with the -l flag to load the math library

bc -l

📋

By default, it will get you trigonometry values in radians.

So let’s say you want to find out the value of the sin 0, then you can use the following:

s(0)

You can do the same with all the trigonometry functions.

And if you want to find out the log values, use the following syntax:

l(number)

Here’s an example of how you use the math library with the bc command:

5. Use the bc command in the bash script for floating point operations

Using the bc command in the bash script is pretty much the same as I explained in how you use the bc command without the bc prompt part.

In simple terms, you use the variable that stores the scale option (if any) and output of the arithmetic operation:

variable=$(echo "scale=no; arithmetic_operation" | bc)

For example, here, I created a simple bash script that asks users to enter two numbers for division and then, it uses the bc command with scale=3 to handle float values:

#!/bin/bash read -p "Enter the first number: " num1 read -p "Enter the second number: " num2 result=$(echo "scale=3; $num1 / $num2" | bc) echo "Output: $result"

If you want to use the above script, then, make sure to make it executable using the chmod command.

When executed, you can expect the following behavior:

how to use the bc command in the bash script

6. Use the bc command using the file

This is quite a convenient way of calculating operations as all you have to do is write the actions only one time in the file and can be used endlessly.

First, create a file with the touch command. I would recommend creating a file with the .bc extension so you can have a better idea about what is inside.