Grep is a command-line tool in Linux that is used to search for text patterns in a file or a stream of text. It uses regular expressions, which are a set of characters and symbols that represent a search pattern. The basic syntax for using grep is:
grep 'pattern' file(s)
For example, to search for the word "example" in a file called "file.txt", you would use the command:
grep 'example' file.txt
You can also use regular expressions to search for more complex patterns. For example, to search for all lines that start with the letter "a" and end with the letter "z", you would use the command:
grep '^a.*z$' file.txt
There are many options available with grep that allow you to customize your search, such as the -i option to ignore case and the -c option to display the number of matches.
grep -i 'example' file.txt # ignore case
grep -c 'example' file.txt # count of matches
You can also use Grep command to search multiple files or recursively search in the directory
grep 'example' file1.txt file2.txt
grep -r 'example' /path/to/directory # recursively search in directory
Overall Grep and regular expression are powerful tool for searching and manipulating text in Linux.