`grep -Rnw '/path/to/somewhere/' -e 'pattern'`
-r or -R is recursive ; use -R to search entirely
-n is line number, and
-w stands for match the whole word.
-l (lower-case L) can be added to just give the file name of matching files.
-e is the pattern used during the search
Along with these, --exclude, --include, --exclude-dir flags could be used for efficient searching