Overview About GREP Command ?

Question

What is Grep Command?

The grep command allows you to search one file or multiple files for lines that contain a pattern.

If Grep is not installed in your system you can install by using the following command.

$ sudo apt-get install grep         #Debian/Ubuntu

$ sudo yum install grep             #RHEL/CentOS/Fedora

Syntax For Grep Commands

grep [options] pattern [files]

Option Description

-b Display the block number at the beginning of each line.
-c Display the number of matched lines.
-h Display the matched lines, but do not display the filenames.
-i Ignore case sensitivity.
-l Display the filenames, but do not display the matched lines.
-n Display the matched lines and their line numbers.
-s Silent mode.
-v Display all lines that do NOT match.
-w Match whole word.

Here Some of the examples for using Grep

1)How to Search a Given word in a single File

grep "String_name" filename

2)How to Search a String in Multiple File

grep "string" FILE_PATTERN

The Above example will used to search the string in multiple files.For Example,We have 2 text files named as textfile1 and textfile2.

Now the following command will use to search the string in these two text files

  grep "search_string"  text*

3)How will do Case insensitive search

Using -i option you can do the case insensitive search.

Syntax

grep -i  "string"  Filename

4)How search a string in recursively

Using -r option will do the recursive search.

grep -r  "string" *

5)How to count the number of Matches

Using -c option you can count the number of matches.

grep -c "string" Filename