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Bash

Read File Line by Line in Bash

Here are a couple of ways for reading file line by line in the Bash shell.

Sagar Sharma

You may find yourself in a situation where you want to use a shell script to read files line by line.

And in this tutorial, I will be covering multiple ways to read file line by line in the bash script.

Reading a file line by line in bash

In this tutorial, I will walk you through two ways to write a bash script by which you can read file line by line:

  • Using read command with a while loop
  • Using the cat command with the while loop

To make things easy to understand, I will be using a simple text file named LHB.txt which contains the following:

1. Ubuntu
2. Arch
3. openSUSE
4. Fedora
5. Slackware

1. Using read command with while loop

As the method name suggests, here, I will be using the read command with the while loop inside the bash script.

First, create and open a simple script file using the following command:

nano read.sh

And paste the following lines (will explain in a moment):

#!/bin/bash

file="LHB.txt"

while read -r line; do
    echo -e "$line\n"
done <$file 

Here,

  • file="LHB.txt": Shows which file I want to work with and in my case, it's LHB.txt.
  • while read -r line; do: Starts while loop and reads lines one by one until there's no line to read and the -r flag will prevent backslash escaping within the lines.
  • echo -e "$line\n": Will print every line and each will be separated by one blank line.
  • done < "$file": It redirects the input from the specified file to the while loop.  

Once done, Save changes and exit from the nano text editor.

Make the script executable using the chmod command as shown:

chmod +x read.sh

And finally, execute the script:

./read.sh
read file line by line in bash

2. Using the cat command with the while loop

In this method, I will be using the cat command to read the file which will make the loop logic simple to understand.

This is the script I will be using:

#!/bin/bash

cat LHB.txt | while IFS= read -r line; do
    echo "$line"
    echo   # Print a blank line
done

Here,

  • cat LHB.txt |: Reads the file content of the LHB.txt file and passes it to piped another argument.
  • while IFS= read -r line; do: It reads lines one by one of the LHB.txt files and. IFS is used to preserve leading and trailing whitespace.
  • echo "$line": Prints the line stored in the line variable.

Once you execute the above command, you can expect the following results:

use cat command to read line by line in bash

Learn bash for free

If you are just getting started or want to brush up on the basics, we have a dedicated series for you:

Bash Tutorial Series for Beginners: Start Learning Bash Scripting
The 10 chapter series will teach the bash scripting essentials.

I hope you will find this guide helpful.

Sagar Sharma