How to read a Specific Line From a File in Linux?

When working with the Linux command line, reading specific lines from text files is a common task. Rather than viewing entire files, you often need to extract just one particular line based on its line number.

This article explores four different methods to read a specific line from a file using various Linux commands and utilities.

Sample File Setup

Let's create a sample file called test.txt to demonstrate these methods

$ nl test.txt
     1  This is line 1, I don't have any interesting data.
     2  This is line 2, I don't have any interesting data.
     3  This is line 3, I don't have any interesting data.
     4  This is line 4, I don't have any interesting data.
     5  This is line 5, interesting data: Linux is awesome!
     6  This is line 6, I don't have any interesting data.
     7  This is line 7, I don't have any interesting data.

The nl command displays the file contents with line numbers. Our goal is to extract line 5, which contains the interesting data.

Method 1 Using Bash Script

You can create a bash script to read a specific line by iterating through the file and counting lines

#!/bin/bash
FILE="$1"
LINE_NO=$2
i=0
while read line; do
    i=$(( i + 1 ))
    test $i = $LINE_NO && echo "$line"
done 

This script accepts two arguments: the filename and target line number. However, it processes the entire file. A more efficient version stops after finding the target line 

#!/bin/bash
FILE="$1"
LINE_NO=$2
i=0
while read line; do
    i=$(( i + 1 ))
    case $i in $LINE_NO) echo "$line"; break;; esac
done 

Usage

$ ./getLine.sh test.txt 5


This is line 5, interesting data: Linux is awesome!


Method 2  Using sed Command

The sed command provides compact one-liners for extracting specific lines. Here are two approaches 

Delete All Except Target Line

$ sed '5!d' test.txt


Print Only Target Line

$ sed -n '5p' test.txt


This is line 5, interesting data: Linux is awesome!


For better performance on large files, add the q (quit) command to stop processing after finding the target line 

$ sed '5!d;q' test.txt
$ sed -n '5{p;q}' test.txt


Method 3  Using awk Command

The awk command can extract a specific line using the built-in NR (Number of Records) variable 

$ awk 'NR==5' test.txt


For better performance, exit after printing the target line 

$ awk 'NR==5{ print; exit }' test.txt


This is line 5, interesting data: Linux is awesome!


Method 4  Using head and tail Commands

You can combine head and tail commands to extract a specific line. The strategy is 

• Use head -n X to get the first X lines

• Pipe the output to tail -1 to get the last line from those X lines

$ head -n 5 test.txt | tail -1

This is line 5, interesting data: Linux is awesome!

Performance Comparison

Conclusion

Linux provides multiple ways to read specific lines from files. For large files, use sed or awk with quit commands for optimal performance. The head and tail combination offers a simple, readable solution for smaller files.