grep

Description

The grep command-line utility is used for searching plain-text data sets for lines that match a regular expression. It is generally used in collaboration with other Linux commands, such as ls, cat, etc., to provide powerful search functionality in files, consoles, IO streams, etc.

Usage

# Search a match string in a file
grep "test" test_file.txt
 
# Recursively search all the files and in the sub-directory
grep -r "test" /some/tmp/dir/*
 
# Get the lines that do not start with a vowel, along with line numbers
grep -v -n -e "^[aeiouAEIOU].*" test_file.txt
 
# Case-insensitive search with 2 lines above and below to display in all the files in the current working directory.
grep -i -A 2 -B 2 "test" *
 
# Get all the details for the wired ethernet network interface\\
ifconfig | grep -A 4 ens*
 
# Get all the Java processes running.
ps aux | grep java

Options

Options	Description
-i	Case-insensitive search
-A 3	display 3 lines below the searched result
-B 2	display 2 lines above the searched result
-C 4	display 4 lines above & below the searched result
-r	recursive search
-v	invert the search result
-c	count the number of searched results
-l	display only the filenames
-e “REGEX”	regex pattern to search
-n	line number of the searched result

Installation

Distro/OS/Package Manager	Install Instruction
Debian/ubuntu	apt install grep
Centos/fedora(dnf, microdnf, rpm, yum)	yum install grep
Arch (pacman)	pacman -S grep
Alpine (apk-docker)	apk –no-cache add grep

References

• Regex online tools regex101 or regexr
• grep cheat sheet
• common uses of grep