Use the Linux grep Command

This article explains how to start using the grep command in Linux®.

What is grep?

You use the grep command within a Linux or Unix-based system to perform text searches for a defined criteria of words or strings. grep stands for Globally search for a Regular Expression and Print it out.

grep syntax

The following example shows the basic command structure:

grep 'string' filename(s)

This command searches for and returns any lines of text that contain the given criteria string in filename(s).

Options:

You can add any of the following options individually or in combination to refine your search:

• -i: Prints lines with matching criteria while ignores casing (Upper/Lowecase).
• -l: Prints filenames only.
• -n: Prints lines with matching criteria and line numbers.
• -c: Prints count of lines with matching criteria.
• -v: Prints lines not matching criteria (inverse search).
• -w: Prints whole word matches.
• -A n: Prints n lines after matches.
• -B n: Prints n lines before matches.
• -C n: Prints n lines before and after matches.

Sample grep commands with output

Example: file "example.txt" contains the following 5 lines:

hello world
Hello World
Hello Worlds
Hello Moon
321 Goodnight

Basic command: Find and print an exact match for "world"

[root@test ~]# grep world example.txt
hello world

Use "-i" to ignore case

[root@test ~]# grep -i world example.txt
hello world
Hello World
Hello Worlds

Use "-n" to find and print matches and include line numbers.

[root@test ~]# grep -n Hello example.txt
2:Hello World
3:Hello Worlds
4:Hello Moon

Use "-c" to find and print the number of line matches.

[root@test ~]# grep -c hello example.txt
1

Use a combination of "-c" and "-i" to refine the search.

[root@test ~]# grep -ci hello example.txt
4

Use "-v" to find and print all inverse (non-matching) lines.

[root@test ~]# grep -v world example.txt
Hello World
Hello Worlds
Hello Moon
321 Goodnight

Use a combination of "-v" and "-i" to refine the search.

[root@test ~]# grep -vi world example.txt
Hello Moon
321 Goodnight

Use "-w" to find and print whole word matches.

[root@test ~]# grep -w World example.txt
Hello World

Use "-A n" to find and print the matches along with "n" lines after the match.

[root@test ~]# grep -A 2 Worlds example.txt
Hello Worlds
Hello Moon
321 Goodnight

Use "-B n" to find and print the matches along with "n" lines before the match.

[root@test ~]# grep -B 2 Goodnight  example.txt
Hello Worlds
Hello Moon
321 Goodnight

Use "CA n" to find and print the match along with "n" lines before and after the match.

[root@test ~]# grep -C 2 Worlds  example.txt
hello world
Hello World
Hello Worlds
Hello Moon
321 Goodnight