recursively search for a value in all files present in a directory

grep -rnw '/path/to/somewhere/' -e 'pattern'

-r or -R is recursive,
-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.

source: https://stackoverflow.com/questions/16956810/how-do-i-find-all-files-containing-specific-text-on-linux