How to search a given pattern (word or string) in files in command line under Linux?

The grep command can be used to find a word or a text (called pattern) in files under Linux:

grep "pattern to search" path

For example, the following command find all files in the current folder containing the string text to find:

grep "text to find" *.*

The following options may also be helpful:

• -r search in subfolder recursively ( or --recursive )
• -i ignore case in search pattern ( or --ignore-case )

The following command search recursively PaTTeRN in sub folders while ignoring case :

grep -i -r "PaTTeRN" path