Bash Script to Print Last N Lines of a File

Use the tail -n N filename command in Bash to print the last N lines of a file, where N is the number of lines you want to see.

Examples

Inputfile.txt content: line1 line2 line3 line4 line5 Command: tail -n 3 file.txt

Outputline3 line4 line5

Inputfile.txt content: apple banana cherry Command: tail -n 1 file.txt

Outputcherry

Inputfile.txt content: one two three four five six seven Command: tail -n 0 file.txt

Output

How to Think About It

To print the last n lines of a file, think about reading the file from the end instead of the beginning. The tail command in Bash is designed to do exactly this by default. You just need to specify how many lines you want with the -n option.

Algorithm

1

Get the number of lines n to print from the user or script argument.

2

Get the filename from the user or script argument.

3

Use the <code>tail -n n filename</code> command to extract the last n lines.

4

Print the output to the screen.

Code

bash

#!/bin/bash

# Check if two arguments are given
if [ "$#" -ne 2 ]; then
  echo "Usage: $0 <number_of_lines> <filename>"
  exit 1
fi

n=$1
file=$2

tail -n "$n" "$file"

Output

line3
line4
line5

Dry Run

Let's trace printing last 3 lines of file.txt containing 5 lines.

1

Input arguments

n=3, file=file.txt

2

Run tail command

tail -n 3 file.txt

3

Output lines

line3 line4 line5

Step	Command	Output
1	Set n=3, file=file.txt
2	tail -n 3 file.txt	line3 line4 line5

Why This Works

Step 1: Using tail command

The tail command reads the file from the end and prints lines.

Step 2: Option -n

The -n option tells tail how many lines to print from the end.

Step 3: Arguments validation

The script checks if the user provides exactly two arguments: number of lines and filename.

Alternative Approaches

Using sed command

bash

sed -n "$(( $(wc -l < filename) - n + 1 )),$ p" filename

This uses sed to print lines from calculated start line to end; less efficient for large files.

Using awk command

bash

awk -v n=3 'NR>=(NR-n+1)' filename

Awk can print last n lines but requires reading whole file; more complex syntax.

Complexity: O(n) time, O(1) space

Time Complexity

The tail command reads only the last part of the file, so it runs in linear time relative to the number of lines requested, not the whole file.

Space Complexity

It uses constant extra space because it streams output without loading the entire file into memory.

Which Approach is Fastest?

tail is fastest and simplest for this task compared to sed or awk which may read the whole file.

Approach	Time	Space	Best For
tail -n	O(n)	O(1)	Quickly printing last lines of large files
sed	O(m)	O(1)	When you want line ranges but less efficient for large files
awk	O(m)	O(1)	Complex processing but slower for just last lines