Search sub directories recursively using grep

Pass the -r option to grep command to search recursively through an entire directory tree. With this option one can search the current directory and and all levels of subdirectories by passing the -r or -R to the grep command. The syntax is:

grep -r 'word-to-search' *

grep -r 'main()' *

grep -r '192.168.1.254' /etc/