How To Use Grep Command In Linux

Grep is an essential Linux and Unix command. It is used to search text and strings in a given file. In other words, grep command searches the given file for lines containing a match to the given strings or words.

The syntax is as follows:

grep 'word' filename
fgrep 'word-to-search' file.txt
grep 'word' file1 file2 file3
grep 'string1 string2'  filename
cat otherfile | grep 'something'
command | grep 'something'
command option1 | grep 'data'
grep --color 'data' fileName
grep [-options] pattern filename
fgrep [-options] words file

How to use grep recursively

You can search recursively i.e. read all files under each directory for a string “192.168.1.5”

$ grep -r "192.168.1.5" /etc/

OR

$ grep -R "192.168.1.5" /etc/

Sample outputs:

/etc/ppp/options:# ms-wins 192.168.1.50
/etc/ppp/options:# ms-wins 192.168.1.51
/etc/NetworkManager/system-connections/Wired connection 1:addresses1=192.168.1.5;24;192.168.1.2;

You will see result for 192.168.1.5 on a separate line preceded by the name of the file (such as /etc/ppp/options) in which it was found. The inclusion of the file names in the output data can be suppressed by using the -h option as follows:

$ grep -h -R "192.168.1.5" /etc/

OR

$ grep -hR "192.168.1.5" /etc/

Sample outputs:

# ms-wins 192.168.1.50
# ms-wins 192.168.1.51
addresses1=192.168.1.5;24;192.168.1.2;