Bash Script to Print Specific Line from File

Use sed -n 'N{p;q;}' filename where N is the line number to print a specific line from a file in Bash.

Examples

Inputfile.txt content: Line1 Line2 Line3 Command: sed -n '2{p;q;}' file.txt

OutputLine2

Inputfile.txt content: Apple Banana Cherry Date Command: sed -n '4{p;q;}' file.txt

OutputDate

Inputfile.txt content: One Two Three Command: sed -n '5{p;q;}' file.txt

Output

How to Think About It

To print a specific line from a file, think of reading the file line by line until you reach the line number you want. Then, print that line and stop reading further to save time.

Algorithm

1

Get the line number N to print.

2

Open the file and read lines one by one.

3

When the current line number equals N, print the line.

4

Stop reading the file after printing the line.

Code

bash

#!/bin/bash

line_number=$1
file=$2

sed -n "${line_number}{p;q;}" "$file"

Output

Line2

Dry Run

Let's trace printing line 2 from a file with content: Line1, Line2, Line3

1

Set inputs

line_number=2, file='file.txt'

2

Run sed command

sed reads lines one by one

3

At line 2

Print 'Line2' and quit

Line Number	Line Content	Action
1	Line1	Skip
2	Line2	Print and quit

Why This Works

Step 1: Use sed with -n option

The -n option tells sed not to print anything by default.

Step 2: Specify line number and commands

The 'N{p;q;}' means: at line N, print (p) and quit (q) immediately.

Step 3: Stop reading after printing

Quitting early saves time by not reading the whole file.

Alternative Approaches

Using awk

bash

awk 'NR==N {print; exit}' file.txt

Awk reads lines and prints the Nth line, then exits early; easy and readable.

Using head and tail

bash

head -n N file.txt | tail -n 1

This reads the first N lines then prints the last one; less efficient for large files.

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

Time Complexity

The script reads lines up to line N, so time grows linearly with N.

Space Complexity

Uses constant extra space since it processes one line at a time.

Which Approach is Fastest?

Using sed or awk with early exit is fastest; head and tail read more lines than needed.

Approach	Time	Space	Best For
sed with quit	O(N)	O(1)	Fast line extraction with minimal overhead
awk with exit	O(N)	O(1)	Readable and efficient for line extraction
head and tail	O(N)	O(1)	Simple but less efficient for large files