$ grep -rnw 'directory' -e "pattern"
-r is recursive, -n is line number and -w stands match the whole word. Along with these, --exclude or --include parameter could be used for efficient searching. Something like below:
$ grep --include={*.c,*.h} -rnw 'directory' -e "pattern"
This will only search through the files which have .c or .h extensions. Similarly a sample use of --exclude: