Round to 2 Decimal Places in Bash

1. Overview

In Bash scripting, dealing with numbers and specifically rounding them to a certain number of decimal places is a common task. For example, given a number like 3.14159, the goal is to round it to two decimal places, resulting in 3.14.

This article explores various methods to achieve this in Bash, focusing on rounding to two decimal places. We will compare each method’s performance and delve into each command’s details.

2. Using printf Command

The printf command in Bash is similar to the printf function in C. It is used to format the output.

Here is the syntax:

Format specifier provides the format of output. In this case, we want to round the number to 2 decimal places, and that’s the reason we can put the format as "%.2f".

The explanation of the above code snippet is as follows:
%.2f is format specifier here.

• % introduces format specifier.
• .2 indicates that the number should be rounded to 2 decimal places.
• f stands for floating-point number.

\n is a newline character to ensure that output is followed by a new line.
$number is a variable containing the number to be formatted.

printf is fast and efficient for formatting numbers. It’s built into the shell and doesn’t require spawning a new process.

3. Using awk Command

The awk is a text processing and data manipulation tool.. We can use the awk command with format specifier as %.2f as below:

The explanation of the above code fence is as follows:

• The echo $number sends the number to the awk command.
• | pipes output of echo to awk.
• Inside awk, {printf "%.2f\n", $0} is action performed on the given input.
  • printf "%.2f\n" is similar to the printf command.
  • $0 represents the entire line of the input, a number in this case.

4. Using bc

The bc is an arbitrary precision calculator language. Let’s use bc to round the number to 2 decimal places.

Please note that above bc command doesn’t round the decimal but truncates to 2 decimal places.

We can use the following command to do the round rather than truncate:

5. Using Python

Invoking Python for arithmetic operations provides high precision and is useful if the script interacts with Python or requires advanced mathematical functions.

• python -c allows running a Python command as a string from the shell.
• print(round(number, 2)) calls Python’s round function, rounding the number to two decimal places.
• The number in the Python command is the shell variable and needs to be passed correctly.

This is an excellent solution in case our script already interacts with Python. If not, it can cause extra overhead due to a call to the external interpreter.

6. Conclusion

In this article, we have discussed different ways to round to 2 decimal places.

printf is fast and efficient for formatting numbers. It’s built into the shell and doesn’t require spawning a new process. This makes it an excellent choice for basic formatting.

bc and awk offer more precision but at the cost of performance. Python is powerful and precise but is the slowest option here due to the overhead of invoking an external interpreter.