In this post,I am sharing a useful option with linux grep command.In this tutorial, we will use grep command to show lines after and before the keyword . As a Linux System Engineer, sometimes I get the requirement to print lines above and below of a particular keyword in the file. Generally if you only use the command like grep keyword filename, it will print only the line which has the keyword.
Print Number of lines AFTER keyword matching lines
Option to use : -A
-A option will print the number of lines after keyword match in the lines.
Syntax
grep -Akeyword [path of filename]
Example : In this example, we are searching the keyword called linux. And the we will print 2 lines after keyword linux
sharad@LinuxMintBox /tmp $ grep -A 2 linux loremipsum.txt linux Open Source country sharad@LinuxMintBox /tmp $
Print Number of lines BEFORE keyword matching lines
Option to use : -B
-B option will print the number of lines before keyword match in the lines.
Syntax
grep -Bkeyword [path of filename]
example : In this example, we are searching the keyword called linux. And the we will print 2 lines before keyword linux
sharad@LinuxMintBox /tmp $ grep -B 4 linux loremipsum.txt green white orange gray linux sharad@LinuxMintBox /tmp $
Print lines after and before of the keyword matching in the file
We can use both option -A and -B in same grep command .
Example.
sharad@LinuxMintBox /tmp $ grep -A 3 -B 4 linux loremipsum.txt green white orange gray linux Open Source country People sharad@LinuxMintBox /tmp $
Note: Many users also use grep with the pipe along cat command.
The below example will give more understanding.
Here, we are searching for linux keyword. Number of lines after keyword is 1 and before keyword is 5.I have used both options.
you can use either -A or -B as per your requirement.
sharad@LinuxMintBox /tmp $ cat loremipsum.txt |grep -A 1 -B 5 linux blue green white orange gray linux Open Source sharad@LinuxMintBox /tmp $