Mastering grep: How to Display Line Numbers Explained

Introduction

grep is a command frequently used for text searching.

The line number display feature is especially useful when you want to confirm which line a search result appears on.

This article explains everything from the basic syntax for displaying line numbers with grep to advanced usage.

Basic Syntax for Displaying Line Numbers with grep

Create File

cat << 'EOF' > input.txt
apple
banana
grape
banana smoothie
orange
EOF

Command

grep -n "banana" input.txt

Output

2:banana
4:banana smoothie

How It Works

Item	Description
grep	Searches for the specified string
-n	Displays the line number at the beginning of each matching line
"banana"	The string to search for
input.txt	The file to search

Explanation

Using grep -n displays line numbers along with the search results.
This is useful when you want to quickly locate the relevant section in a configuration file or log file.

Displaying grep Search Results with Line Numbers and Filename

Create File

cat << 'EOF' > input.txt
apple
banana
orange
apple juice
grape
EOF

Command

grep -nH "apple" input.txt

Output

input.txt:1:apple
input.txt:4:apple juice

How It Works

Option	Description
grep	Command that searches for the specified string
-n	Displays the line number of each matching line
-H	Displays the filename at the beginning of each search result
"apple"	Search keyword
input.txt	File to search

Explanation

Using grep -nH displays both the line number and filename alongside the search results.
When searching multiple files, this lets you quickly identify which file and which line number a match was found on.

Listing Line Numbers Across Multiple Files with grep

Create File

cat << 'EOF' > file1.txt
apple
banana
orange
banana
EOF

Create File

cat << 'EOF' > file2.txt
grape
banana
melon
EOF

Create File

cat << 'EOF' > file3.txt
banana
peach
banana
EOF

Command

grep -n "banana" file1.txt

Output

2:banana
4:banana

Command

grep -n "banana" file2.txt

Output

2:banana

Command

grep -n "banana" file3.txt

Output

1:banana
3:banana

Command

grep -n "banana" file*.txt

Output

file1.txt:2:banana
file1.txt:4:banana
file2.txt:2:banana
file3.txt:1:banana
file3.txt:3:banana

How It Works

Item	Description
grep	Command for text searching
-n	Option to display the line number of each matching line
file*.txt	Specifies file1.txt, file2.txt, and file3.txt together
Output format	filename:line number:matching line
Use case	Checking the location of a target string across multiple files at once

Explanation

Using grep -n lets you see the line numbers of matching strings.
When multiple files are specified at once, the filename and line number are both shown, making it easy to quickly locate the relevant section.

Recursive Directory Search with Line Numbers Using grep

Create File

cat << 'EOF' > input.txt
src/main.py:10:def main():
src/main.py:25:print("hello")
src/utils/helper.py:8:def helper():
docs/readme.md:15:How to use grep
logs/app.log:100:ERROR failed
EOF

Create File

mkdir -p src/utils docs logs

Create File

awk -F: '{print $2 ":" $3}' input.txt > src/main.py

Create File

awk -F: 'NR==3{print $2 ":" $3}' input.txt > src/utils/helper.py

Create File

awk -F: 'NR==4{print $2 ":" $3}' input.txt > docs/readme.md

Create File

awk -F: 'NR==5{print $2 ":" $3}' input.txt > logs/app.log

Command

grep -rn "grep" .

Output

src/main.py:4:15:How to use grep
docs/readme.md:1:15:How to use grep

Command

grep -rn "def" .

Output

src/utils/helper.py:1:8:def helper()
src/main.py:1:10:def main()
src/main.py:3:8:def helper()

How It Works

Item	Description
grep	Command for searching text
-r	Recursively searches within a directory
-n	Displays the line number of each matching line
"grep"	The string to search for
.	Searches within the current directory and below

Explanation

Using grep -rn lets you recursively search within a directory while displaying the line number of each matching line.
This is commonly used for source code investigation and configuration file searches.

Displaying Line Numbers Only for Exact Word Matches with grep

Create File

cat << 'EOF' > input.txt
apple
banana
orange
apple pie
grape
apple
EOF

Command

grep -nx "apple" input.txt

Output

1:apple
6:apple

How It Works

Option	Description
grep	Searches for the specified string
-n	Displays the line number of each matching line
-x	Matches only when the entire line exactly matches the search string
"apple"	The string to search for
input.txt	File to search

Explanation

Using -x excludes partial matches like "apple pie" and targets only lines that exactly match "apple".

Combining with -n lets you confirm only the line numbers of matching lines.

Case-Insensitive Search with Line Numbers Using grep

Create File

cat << 'EOF' > input.txt
Apple
banana
APPLE
Orange
apple pie
EOF

Command

grep -in "apple" input.txt

Output

1:Apple
3:APPLE
5:apple pie

How It Works

Option	Description
grep	Searches for lines containing the specified string
-i	Searches without distinguishing between uppercase and lowercase
-n	Displays the line number of each matching line
"apple"	Keyword to search for
input.txt	File to search

Explanation

Using grep -in searches case-insensitively and simultaneously displays the line numbers of matching lines.
This is useful for quickly locating target lines during log analysis or configuration file inspection.

Searching for Lines Matching Specific Patterns with Line Numbers Using Regex in grep

Create File

cat << 'EOF' > input.txt
apple
banana
error: file not found
orange
warning: low disk space
grape
error: permission denied
melon
EOF

Command

grep -n '^error:' input.txt

Output

3:error: file not found
7:error: permission denied

How It Works

Element	Description
grep	Command that searches text for lines matching a condition
-n	Displays the line number at the beginning of each matching line
^	Regular expression representing the start of a line
error:	The string to search for
'^error:'	Regular expression that extracts only lines beginning with "error:"

Explanation

Using grep -n lets you simultaneously confirm matching lines and their line numbers.
Combining with regular expressions allows you to efficiently search for lines matching a specific pattern in log files and similar use cases.

Searching for Line Numbers with Multiple Keywords Using OR Conditions in grep

Create File

cat << 'EOF' > input.txt
grep is a command for string searching
sed is used for line editing
Use the -n option to display line numbers
awk can also handle line numbers
grep can search for multiple keywords
EOF

Command

grep -nE 'grep|line|number' input.txt

Output

1:grep is a command for string searching
2:sed is used for line editing
3:Use the -n option to display line numbers
4:awk can also handle line numbers
5:grep can search for multiple keywords

How It Works

Element	Description
grep	Text search command
-n	Displays the line number at the beginning of each matching line
-E	Enables extended regular expressions
grep\|line\|number	OR condition (grep or line or number)
input.txt	File to search

Explanation

Using grep -nE lets you search with multiple keywords joined by | as OR conditions.
Matching lines are assigned line numbers, allowing you to quickly locate the relevant sections.

Searching for Line Numbers with Multiple Keywords Using AND Conditions in grep

Create File

cat << 'EOF' > input.txt
Basic usage of grep
How to display line numbers with grep using -n
How to handle line numbers with awk
Example of combining grep and line numbers
Searching with multiple conditions in grep
Running a grep search with line numbers
Combining sed and grep
Sample containing grep line number
Line containing grep only
Line containing line numbers only
EOF

Command

grep -n 'grep' input.txt | grep 'line' | grep 'number'

Output

2:How to display line numbers with grep using -n
4:Example of combining grep and line numbers
6:Running a grep search with line numbers
8:Sample containing grep line number

How It Works

Item	Description
grep -n 'grep' input.txt	Searches for lines containing "grep" and displays line numbers
grep 'line'	Extracts only lines containing "line" from the previous result
grep 'number'	Further extracts only lines containing "number"
Pipe (\|)	Passes the output of the previous command to the next command
AND search	Only lines that pass all grep conditions remain

Explanation

AND searches with multiple keywords can be achieved by chaining grep commands with pipes.
Adding the -n option lets you simultaneously confirm the line numbers of matching lines.

Displaying Line Numbers for Non-Matching Lines with grep

Create File

cat << 'EOF' > input.txt
apple
orange
banana
grape
EOF

Command

grep -vn "apple" input.txt

Output

2:orange
3:banana
4:grape

How It Works

Option	Description
grep	Performs pattern searching
-v	Displays lines that do not match
-n	Displays the line number at the beginning of each line
"apple"	The search string to exclude
input.txt	File to search

Explanation

The -v option in grep extracts lines that do not match the search condition, and -n displays their line numbers.
This lets you simultaneously confirm the line numbers and content of non-matching lines.

Displaying Surrounding Lines with Line Numbers Using grep

Create File

cat << 'EOF' > input.txt
apple
banana
orange
grape
banana
melon
banana
peach
EOF

Command

grep -n -B 1 -A 1 "banana" input.txt

Output

1-apple
2:banana
3-orange
4-grape
5:banana
6-melon
7:banana
8-peach

Command

grep -n -C 2 "banana" input.txt

Output

1-apple
2:banana
3-orange
4-grape
5:banana
6-melon
7:banana
8-peach

How It Works

Option	Description
-n	Displays the line number of each matching line
-B <num>	Displays the specified number of lines before each matching line
-A <num>	Displays the specified number of lines after each matching line
-C <num>	Displays the specified number of lines before and after each matching line

Explanation

Using grep's -n option lets you confirm the line numbers of matching lines.

Combining with -A, -B, and -C also lets you view the surrounding context of matching lines.

Getting the Line Number of the First Match with grep

Create File

cat << 'EOF' > input.txt
apple
banana
orange
banana smoothie
grape
EOF

Command

grep -nm1 "banana" input.txt

Output

2:banana

Command

grep -nm1 "banana" input.txt | cut -d: -f1

Output

How It Works

Item	Description
grep	Searches for lines matching a pattern
-n	Displays the line number of each matching line
-m1	Stops searching after the first match is found
cut -d: -f1	Extracts only the line number from the "line number:content" format
Result	Retrieves line number 2, where "banana" first appears

Explanation

grep -n outputs search results with line numbers, and combining with -m1 retrieves only the first matching line.
When only the line number is needed, use cut to extract it.

Getting the Line Number of the Last Match with grep

Create File

cat << 'EOF' > input.txt
apple
banana
orange
banana
grape
banana
EOF

Command

grep -n 'banana' input.txt | tail -n 1

Output

6:banana

Command

grep -n 'banana' input.txt | tail -n 1 | cut -d: -f1

Output

How It Works

Item	Description
grep -n	Outputs matching lines in "line number:content" format
grep -n 'banana' input.txt	Retrieves all lines matching "banana"
tail -n 1	Retrieves the last line of the matching results
cut -d: -f1	Retrieves only the portion before the delimiter : (the line number)
Result	Retrieves line number 6, where "banana" last appears

Explanation

Since grep alone cannot directly retrieve only the last matching line number, tail -n 1 is used in combination. Adding cut lets you retrieve only the line number without the line content.

Extracting Only Matching Line Numbers with awk from grep Output

Create File

cat << 'EOF' > input.txt
apple
banana
orange
banana
grape
banana
EOF

Command

grep -n 'banana' input.txt

Output

2:banana
4:banana
6:banana

Command

grep -n 'banana' input.txt | awk -F: '{print $1}'

Output

2
4
6

How It Works

Command	Role
grep -n 'banana' input.txt	Outputs matching lines and their line numbers in "line number:content" format
awk -F: '{print $1}'	Uses : as the delimiter and extracts only the first column (line number)
grep -n 'banana' input.txt \| awk -F: '{print $1}'	Retrieves only the line numbers of matching lines

Explanation

Using grep's -n option assigns line numbers to matching lines.
Processing that output with awk makes it easy to extract only the matching line numbers.

Editing a Specific Line Using Line Numbers from grep Combined with sed

Create File

cat << 'EOF' > input.txt
apple
banana
orange
grape
melon
EOF

Command

grep -n '^orange$' input.txt

Output

3:orange

Command

sed -i '' '3s/orange/lemon/' input.txt

Command

cat input.txt

Output

apple
banana
lemon
grape
melon

How It Works

Item	Description
grep -n	Displays each line with its line number prepended
^orange$	Searches for lines that exactly match "orange"
3:orange	Indicates that "orange" exists on line 3
sed '3s/orange/lemon/'	Replaces "orange" with "lemon" on line 3
-i	Updates the file directly

Explanation

Using grep -n lets you confirm the line number of a target string.
Passing the confirmed line number to sed allows you to safely edit only that specific line.

Tips for Speeding Up Line Number Searches in Large Files with grep

Create File

cat << 'EOF' > input.txt
INFO startup completed
INFO loading modules
ERROR database connection failed
INFO retrying connection
INFO retry successful
WARN disk usage 80%
INFO processing request
ERROR timeout detected
INFO processing request
INFO shutdown completed
EOF

Command

grep -n "ERROR" input.txt

Output

3:ERROR database connection failed
8:ERROR timeout detected

Command

LC_ALL=C grep -n "ERROR" input.txt

Output

3:ERROR database connection failed
8:ERROR timeout detected

Command

grep -n -m 1 "ERROR" input.txt

Output

3:ERROR database connection failed

How It Works

Tip	Mechanism	Effect
-n	Displays line numbers alongside matching lines	Instantly confirms line numbers in grep searches
LC_ALL=C	Disables locale processing and searches byte by byte	Speeds up searching in large files
-m 1	Stops searching after the specified number of matches	Faster when only the first match is needed
Use specific search strings	Reduces unnecessary match evaluations	Lowers CPU load
Target non-compressed files	Avoids decompression processing	Reduces I/O time

Explanation

When performing line number searches in large files with grep, disabling locale processing via LC_ALL=C is one of the most effective ways to speed things up.

If only the first match is needed, combining the -m option avoids unnecessary scanning.

Key Points for Displaying Line Numbers with grep

The line number display feature in grep is a fundamental capability for quickly grasping the location of search targets.

It can be applied not only to single files but also to searches across multiple files or entire directories.

Furthermore, combining it with regular expressions, conditional searches, and tools like awk and sed enables more advanced text processing.

Mastering grep's line number feature will allow you to efficiently carry out log analysis and configuration file review tasks.