GREP command in linux / unix

GREP command searches the file for a lines match to a string, words, or characters we pass on.
Syntax: grep [-option] 'search word' /path/to/file

Options are as follows:

• -i : to ignore word case.
• -r : recursively read files under each directory.
• -w : to get the matching word only.
• -c : to count number of lines that the search word matches.
• -P : to use regex command within the grep command.
• -l : to list the file names matching the search word.
• -v : to get lines that doesn't match the search word.

Sample GREP commands:

- default grep command without using an option.
$ grep 'word' /path/to/file

- ignoring word cases and matches
$ grep -i 'word'/path/to/file

- using regex to get all the lines that matches
$ grep -P "word1|word2" /path/to/file
$ grep -P "^word3" /path/to/file

- matching the exact words in a line
$ grep -w "word" /path/to/file

- get the file names that matches the search word.
$ grep -l "init()" /path/to/file*

- invert matches to the line
$ grep -v "word" /path/to/file

- grep command combining options and uses pipe to execute next grep command.
$ grep -ivP "word1|word2" /path/to/file
$ grep -i "word" /path/to/file | grep -vP "word2"