Write a Bash Script to Print a Particular Line From a File

One useful tool for automating operations in Unix-based systems is bash scripting. The need to print a certain line from a file is one such requirement. This post will walk you through writing a basic Bash script that accomplishes that. The fundamentals of utilizing conditional statements, showing the intended output, and reading user input will all be covered.

Prerequisites

Before we begin to write the script, make sure you have:

• A Unix-based operating system (Linux, macOS, etc.)
• A text editor (like Nano, Vim, or any other preferred editor)

How to Write a Bash Script to Print a Particular Line from a File?

Below is the how-to Write a bash script to print a particular line from a file.

Step-by-Step Guide

1. Create the Bash Script File

Open your terminal and create a new file for your script. We’ll call it print_line.sh. You can create this file using the touch command or by directly opening it in a text editor.

Command: touch print_line.sh

2. Open the Script in a Text Editor

Now, open the script in your preferred text editor. For example, if you are using nano, you can type:

nano print_line.sh

3. Write the Shebang

At the top of the script, add the shebang line. This line tells the system which interpreter to use to execute the script.

#!/bin/bash

4. Read User Input

Next, we’ll add commands to read the filename and the line number from the user. We will also check if the file exists.

echo "Enter the filename:"
read filename

if [[ ! -f $filename ]]; then
    echo "File not found!"
    exit 1
fi

echo "Enter the line number you want to print:"
read line_number

5. Print the Specified Line

Now, we will use the sed command to print the specified line from the file. The sed command is a stream editor that can perform basic text transformations.

line_content=$(sed -n "${line_number}p" "$filename")
echo "Line $line_number: $line_content"

6. Complete Script

Your complete script should look like this:

#!/bin/bash

echo "Enter the filename:"
read filename

if [[ ! -f $filename ]]; then
    echo "File not found!"
    exit 1
fi

echo "Enter the line number you want to print:"
read line_number

line_content=$(sed -n "${line_number}p" "$filename")
echo "Line $line_number: $line_content"

7. Save and Exit

If you are using nano, save your changes by pressing CTRL + O, then hit Enter, and exit by pressing CTRL + X.

8. Make the Script Executable

Before you can run the script, you need to make it executable. Use the following command:

chmod +x print_line.sh

9. Run the Script

Now you can execute your script. Run it by typing:

./print_line.sh

10. Input File and Line Number

When prompted, enter the filename and the line number you wish to print. For example:

• Enter the filename: sample.txt
• Enter the line number you want to print: 3

If the file exists and the line number is valid, the script will output the specified line.

Conclusion

An easy way to showcase the capabilities of shell scripting is to create a Bash script that prints a specific line from a file. This script is easily customizable for more complex tasks or may be integrated into larger scripts for automation by using simple commands and user input.