grep

grep -r --include='*.c' --include='*.h' -e 'search this' -e 'search this, too' in_this_dir/

-i ignore case

-e PATTERN to enable to search for multiple patterns or patterns beginning with -

-w word matching

-L print file names only. result invered.

-l print file names only

-A NUM print lines after a line found

-B NUM print lines before a line found

-C NUM print lines around a line found

--exclude=GLOB excluding some files

--exclude-dir=DIR excluding a directory

--include=GLOB including some files only

-R or -r recursively