---
title: "Bash: How to Calculate Sum After Reading File"
description: "Here is a shell script to calculate the sum of input file records. And to replace a string with a new one using sed utility."
url: https://srinimf.com/2021/11/15/bash-how-to-calculate-sum-after-reading-file/
date: 2021-11-15
modified: 2026-10-10
author: "Srini"
image: https://i0.wp.com/srinimf.com/wp-content/uploads/2021/11/pexels-photo-2411520.jpeg?fit=1880%2C1253&ssl=1
categories: ["Shell scripts"]
tags: ["Sed in Shell script", "Sed with file processing"]
type: post
lang: en
---

# Bash: How to Calculate Sum After Reading File

Here’s a bash script that reads an input file and calculates the sum. A file containing a couple of records is an input for this script. The script reads this file using While (loop) and checks for a specific string; If found, further, it gets a substring of numbers for some calculation.

*Bash script reading input file*

## Reading file and calcuate sum

- The **read – r** command reads the file. The While loop reads till the end of the file. Added if logic to test the string.
- The **sed utility** formats the input record as desired. When the matched string is received, it will then get a number (used substring concept). Then, the echo statement displays the calculated sum.

## Input file

```
app1:
cpu:1500m
mem:10
app2:
cpu:200m
mem:20
```

## Script logic

The result would be the [sum of](https://srinimf.com/2021/11/22/how-to-find-sum-of-series-in-python/) app1 memory and app2 memory. It gives 10+20=30.

![script logic with sed utility usage](https://i0.wp.com/srinimf.com/wp-content/uploads/2021/11/bash-sed.png?resize=713%2C489&ssl=1)

### What it does?

- It replaces the ‘m’ that is found in the ***cpu***. Also, it calculates the sum of the mem of app1 and app2 values.
- The read -r line reads input. The file name inputfile.txt works as an input to the While loop. The sed output, it writes to Output.txt file.
- When the string matches to ‘mem’ it gets a number from it. This is later will use it to calculate the sum.
- This is a tricky shell script and may ask in interviews.
- The >> says it appends to output.txt file. If you use > each time it overwrites.

**Result**

Here’s the output from this script. You can see a display of the sum. Also, you can see the output file details without ‘m’ for ***cpu*** value.

![Output of sed utility in script](https://i0.wp.com/srinimf.com/wp-content/uploads/2021/11/result-sed.png?resize=720%2C264&ssl=1)

[Heart-beat monitor](https://amzn.to/3CCDX8J)

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