Best Linux Grep Command Examples

In this article, we are going to learn how to use Linux grep command in Linux. GREP stands for Global Regular Expression Print. Linux grep command is used to search in Linux and Unix. Here we are going to learn some very important and useful Linux Grep command examples.

Best Linux Grep Command Examples

Best Linux Grep Command Examples

Best Linux Grep Command Examples:

Syntax to Use grep command :

grep [Options] [String for Search] [File Path]

Search for a String using Linux grep command

I have a file named file.txt with some text’s as shown in the output below.

[[email protected] ~]# cat file.txt 
Linux is a Open Source Operating System.

LINUX IS A OPEN SOURCE OPERATING SYSTEM.

linux is a open source operating system.

Let’s search for a string i.e. Linux from file file.txt.

[[email protected] ~]# grep linux file.txt  # Search for a String
linux is a open source operating system.

Color the Searched String

Search for a string by highlighting in color using grep command with option – -color.

[[email protected] ~]# grep --color linux file.txt   # Search for string by Highlighting it with color
linux is a open source operating system.

Let’s take one more example. Here I am searching for user itsmarttricks in /etc/passwd file using grep command.

[[email protected] ~]# cat /etc/passwd | grep --color itsmarttricks   # Searching for a User using grep Command
itsmarttricks:x:501:501::/home/itsmarttricks:/bin/bash

You also can search for an Installed Package. Here I am searching if vsftpd package is installed or not.

[[email protected] ~]# rpm -qa | grep vsftpd   # Searching for a Installed Package
vsftpd-2.2.2-24.el6.x86_64

Search for Case Insensitive strings using grep command

We can search Case Insensitive strings using grep command with argument -i. Here I am searching for string Linux and you will able to notice on the output below that I able to search all the strings whether it contains Uppercase or Lowercase.

[[email protected] ~]# grep --color -i linux file.txt   # Searching for Case Insensitive Strings
Linux is a Open Source Operating System.
LINUX IS A OPEN SOURCE OPERATING SYSTEM.
linux is a open source operating system.

Search a String in Multiple Files using grep command

You can search for a string from multiple files. Here I have a directory named data which contains two files i.e. a.txt and b.txt. and I am going to search for string Linux from both the files. Refer to the sample output below.

You can see in the output below we are able to search for the string Linux from both the files and the output show’s the searched string with the file name from which it searched.

[[email protected] data]# pwd
/root/data
[[email protected] data]# ls
a.txt  b.txt
[[email protected] data]# grep --color -i linux a.txt b.txt  # Searching from Multiple Files
a.txt:linux is a open source operating system.
b.txt:Linux is a Open Source Operating System.

Search for Multiple strings

You can search for multiple strings. Here I am searching for strings i.e. Linux, itsmarttricksOpen from file.txt.

[[email protected] ~]# grep -i 'linux\|itsmarttricks\|Open' file.txt   # Search for Multiple Strings
Linux is a Open Source Operating System.
LINUX IS A OPEN SOURCE OPERATING SYSTEM.
linux is a open source operating system.
welcome to itsmarttricks.com
i love itsmarttricks.com

Search for a String in Multiple Files using Wild Card

We can use a wildcard to search with the grep command. For example, here I am searching for string Linux from all available text files. Refer to the command below.

Syntax :  grep -i [string] [path of .txt files]

[[email protected] data]# ls
a.txt  b.txt  c.txt
[[email protected] data]# grep -i linux *.txt   # Searching from all .txt files
a.txt:linux is a open source operating system.
b.txt:Linux is a Open Source Operating System.
c.txt:LINUX IS A OPEN SOURCE OPERATING SYSTEM.

Search for Invert Match using grep command

Another nice feature we have in the grep command is inverted search. Invert search means It will search only those lines which don’t contain the searched string. For example, here I am searching for the string itsmarttricks, In that case, grep will search only those lines which are don’t contains itsmarttricks string.

[[email protected] ~]# cat file.txt 
Linux is a Open Source Operating System.

LINUX IS A OPEN SOURCE OPERATING SYSTEM.

linux is a open source operating system.

welcome to itsmarttricks.com

i love itsmarttricks.com
[[email protected] ~]# grep -v itsmarttricks file.txt  # Search for Invert Match
Linux is a Open Source Operating System.

LINUX IS A OPEN SOURCE OPERATING SYSTEM.

linux is a open source operating system.

Search by Matching Number Regex using grep Command

we can use grep command to Search by using regex. For example, here I am using regex 0-9. means grep will search all those lines which contains any one number from 0 to 9. Refer to the command below.

[[email protected] ~]# grep '[0-9]' test.txt  # Searching using Regex
1
2
3
4
5
20 grep command with examples
6
7
8
9
0

Like the number Regex, we can also set Regex for letters like a-z. Refer to the command below.

[[email protected] ~]# grep '[a-z]' file.txt  # Searching using Regex
Linux is a Open Source Operating System.
linux is a open source operating system.

[[email protected] ~]# grep -i '[a-z]' file.txt  # Searching using Regex Case Insensitively
Linux is a Open Source Operating System.
LINUX IS A OPEN SOURCE OPERATING SYSTEM.
linux is a open source operating system.

Search Recursively using grep command

To search for a string on a directory and also on all sub-directory contained by that directory recursively. Here I have a directory named data which contains some txt files with some content and also have a sub-directory named testing (i.e. /data/testing) which also contains some txt files.

So here I am going to search for the string Linux in directory data and also in all subdirectories contained by it using grep command with argument -r. Refer to the command below.

[[email protected] ~]# cd data/
[[email protected] data]# pwd
/root/data
[[email protected] data]# ls
test1.html  test1.txt  test2.html  test2.txt  test3.html  test3.txt  testing
[[email protected] data]# cd testing/
[[email protected] testing]# pwd
/root/data/testing
[[email protected] testing]# ls
test1.html  test1.txt  test2.html  test2.txt  test3.html  test3.txt

[[email protected] ~]# grep -r "linux" data/  # Searching Recursively
data/test3.html:welcome to itsmarttricks.com
data/testing/test3.html:welcome to itsmarttricks.com
data/testing/test2.html:welcome to itsmarttricks.com
data/testing/test1.html:welcome to itsmarttricks.com
data/test2.html:welcome to itsmarttricks.com
data/test1.html:welcome to itsmarttricks.com

Print the Line Number of Searched String using grep command

grep command with argument -n will show you the line number where the string is available in the file. Here I am searching for the user itsmarttricks in /etc/passwd file.

As you can see on the sample output below it’s available online number 31 in /etc/passwd file.

[[email protected] ~]# grep -n itsmarttricks/etc/passwd  # Searching the Line Number Where the String is Available in the File
31:itsmarttricks:501:501::/home/itsmarttricks:/bin/bash

Print the Number of Matches found for searched string

grep command with argument -c will show give you the count of the total number of times the string is repeated in the file.

[[email protected] ~]# grep -i -c open file.txt  # Searching for the count of Numeber of times the string is repeated in the File
3
[[email protected] ~]# cat file.txt 
Linux is a Open Source Operating System.

LINUX IS A OPEN SOURCE OPERATING SYSTEM.

linux is a open source operating system.

welcome to itsmarttricks.com

Search for exact matched String

You can search for an exact matched string using grep command with argument -w. Now you might think that what is an exact matching string. Suppose you are searching for the string Linux then grep searches for all that word that contains Linux like itsmarttricks, linuxbookslinuxtraining, and so on. So here exact match means it will only search if the word is linux and not any other.

[[email protected] ~]# grep -w "welcome" file.txt  # Searching for Exact matched String
welcome to itsmarttricks.com

Search for an exact matched Line

Like exact matched string you can search for exactly matched line using grep command with argument -x. Refer to the command below.

[[email protected] ~]# grep -x "linux is a open source operating system." file.txt   # Searching for Exact matched Line
linux is a open source operating system.
[[email protected] ~]# grep -x "linux is a open source operating" file.txt 

Search by Anchor Match

You can search by matching the anchor at the start and end of the line. For example, if you want to search for some line that starts with the string welcome then you can use regex ^welcome. Refer to the command below.

[[email protected] ~]# grep ^welcome file.txt  # Searching by Matching anchor at start of the Line
welcome to itsmarttricks.com

If you want to search for some line that ends with the string com then you can use regex com$. Refer to the command below.

[[email protected] ~]# grep com$ file.txt   # Searching by matching anchor at end of the Line
welcome to itsmarttricks.com
i love itsmarttricks.com

Check the Version installed grep Package

You can check the version of the installed grep package using grep command with argument -V.

[[email protected] ~]# grep -V   # Checking for Installed grep package version
GNU grep 2.6.3

Copyright (C) 2009 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

For more grep, command options use the below command on your Linux system.

[[email protected] ~]# man grep  # For more grep command options

Also Read – Best Linux Du Command With Examples

That’s all, In this article, we have explained the Best Linux Grep Command Examples. I hope you enjoy this article. If you like this article, then just share it. If you have any questions about this article, please comment.

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ITSmarttricks Team

This is Mangesh Dhulap the Founder and Editor of IT SMART TRICKS have 6+ years of Industrial Experience. We expect from our visitors to like, share, and comment on our posts.

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