grep many files while printing file name

A useful trick I found:

find . -exec grep -n hello /dev/null {} \;

Including more than one file makes grep print the file name as well as the line number. So we use the handy /dev/null as one extra file to do the job.

Attribution: http://www.linuxquestions.org/questions/programming-9/find-grep-command-to-find-matching-files-print-filename-then-print-matching-content-328036/